A Quarterly Publication of
The Smith-Kettlewell Eye Research Institute’s
Rehabilitation Engineering Research Center
William Gerrey, Editor
Issue: SKTF -- Fall 1984
Original support provided by:
The Smith-Kettlewell Eye Research Institute
and the National Institute on Disability and Rehabilitation Research
Note: This archive is provided as a historical resource. Details regarding products, suppliers, and other contact information are original and may be outdated.
Questions about this archive can be sent to
TABLE OF CONTENTS
by Mr. Albert Yeo
This paper does not pretend to be comprehensive. It is an attempt to set down for your reference some information which may be of use to the person who wishes to know about how to buy, use, or make, screws, bolts, nuts, taps and dies.
First of all, let us clear the decks. It is very common practice to refer to anything which has a thread on its surface as a screw. This is not strictly correct.
A "screw" is a piece of round section material (rod) which has a thread on the outer surface, and which tapers down as it approaches one end of the rod. A screw may or may not have a head at the end farthest from the tapered end. More of this later.
Screws are usually intended to cut their own thread into the material into which they are being inserted. The two most common types of screws are: 1) the wood screw and, 2) the so-called "self-tapping" screw. The wood screw is self-explanatory. The self-tapping screw is intended for use with materials such as thin sheet steel, aluminum, plastics, fibre boards, etc. It differs from the wood screw in two main ways:
Firstly, whereas the wood screw tapers to a sharp point for piercing the wood, the self-tapper does not have a sharp point. Rather, it ends with a very short section of rod which has a diameter equal to about one-third that of the main part of the threaded rod.
If you wish to use one of these self-tappers, say to join two pieces of sheet metal together, you must first drill a hole through both pieces of metal. The size of this hole should be the same as the short piece of rod at the narrowest part of the taper. Of course, before joining the two pieces of metal, they must be firmly clamped together. The screw is then inserted and driven firmly home.
Secondly, the spiral of the thread on a self-tapper is steeper than that on a wood screw. As the self-tapper makes its way through the material, it cuts a shallow thread on the inside of the hole, and if the screw is removed, and then re-inserted, this thread might be damaged; this will enlarge the hole. If this happens, a larger screw may have to be used.
Nuts and Bolts
A bolt is a length of rod with or without a head, having a thread cut on its outer surface and with no taper. The spiral thread is much shallower than that of a screw.
There are literally hundreds of different threads about these days, and we shall only deal with the more standard ones in this article. Some larger manufacturing companies use their own (non-standard) threads, and we shall not treat these here.
Bolts are used in one or other of two ways:
- In one case (where the material is thick enough) a so-called "clearance hole" is drilled through the material which will be nearest to the head of the bolt. The bolt can thus be passed easily through it. The hole in the piece of metal which is to be farthest from the head is smaller than the diameter of the bolt and is designated a "tapping" sized hole. The thread is then cut on the inside of the smaller hole, the bolt is passed through the metal which has the clearance hole; its thread is then engaged with that of the tapped hole. The bolt is then rotated until the head is in firm contact with the surface of the metal.
- Sometimes this system is used with a bolt that does not have a head. Such a bolt is often referred to as a "stud."
- In the second case, the clearance hole is drilled through both pieces of metal. The bolt is passed through them both; a nut is run up the bolt and tightened home. It is good practice to provide a "washer" immediately under the head of the bolt,
and another under the nut.
- The washer can be of any shape or size, though generally it will be a disc which is slightly larger than the nut or the head of the bolt, and having a clearance hole in its center. The use of washers makes it possible to tighten the nut and bolt without damaging the surface of the metal. The theory is that when the nut is rotated, the washer stays still.
- Where the device, of which the nut and bolt is to be a part, will be subject to vibration, it is a good plan to place a "spring washer" (sometimes called "lock washer") between the plain washer and the nut.
The spring washer is smaller than the plain washer. It has a clearance hole in the center. It is cut through at one point from the hole to the outer edge. The two cut edges are pushed in opposite directions, and in a direction which is at right angles to the main surface, until a small gap appears. The spring washer is then hardened and tempered. The final product looks like a single turn cut from a spiral spring.
- The nut is thicker than the washer and can be of any shape, but mostly it will be hexagonal (six-sided). It has a tapping sized hole in its center and has a thread cut on its inner surface to match that of the bolt.
Taps and Dies
A tap is used to cut a thread on the inside of a hole. A die is used to cut a thread on the outside of a bolt.
Although the tap and the die are very different in appearance, your actions when using them are the same. The movements and principles involved apply to them both.
A tap is made from a piece of rod between one and four inches long. The thread is cut on the outside reaching from the one end to about two-thirds of the way from this end. Three or four slots (or channels) are cut along the length starting at one end and finishing about two-thirds of the way along from that end. The rest of the rod is left plain, except for a short length at the top, which is made square. This is so that the tap can be held firmly in its holder.
Tap holders come in a wide variety. They all have some way of holding the square end of the tap, and they usually have a T-shaped handle. The simplest form has a large round or hexagonal metal plate with two handles pressed into opposite edges; a square hole in the center accepts the tap, and a setscrew secures it in place. Others take the form of a drill chuck, except that they have a square throat to keep the tap from turning. Whatever the style, it is important that the tap be held very firmly in its holder, as you
The flutes are the part of the tap which will actually cut the thread into your work.
Suppose we wish to cut a thread on the inside of a hole in a piece of steel plate, say, about 1/4" thick.
The first thing to do is to secure the plate firmly in a vise or other stable clamp. The surface of the plate must be perfectly horizontal with reference to all points of the compass.
Fix a tap firmly in its holder and place its end in the hole in the steel plate. Now rotate the tap two-thirds of a turn using a constant, gentle but firm, downward pressure. Stop, then reverse the direction of rotation for one-third of a turn. Continue thus, two steps forward, one step back, until you feel the tap is really cutting. At this point the tap will stay upright on its own. It is vital that you keep the tap absolutely vertical at all times. Otherwise, because it is hard, and therefore brittle, it may break off flush with the surface of the steel; it will then be very difficult--often impossible--to remove the broken piece of tap.
Standard threads are always cut clockwise. When I say, "rotate the tap forward," this means in a clockwise direction. This means that the left hand goes away from you while the right hand comes towards you.
A reverse thread (one which runs counterclockwise) is sometimes used for specific purposes. You would need special taps and dies to cut these threads; these are more
likely to be of use to a mechanical engineer than to an electronic technician.
Take a handle of the tap holder in each hand and move both hands at exactly the same speed, and with exactly the same pressure. You will get the hang of it after a little practice and perhaps the loss of a tap or two. It is a job which takes plenty of patience.
Continue the two forward, one back, until all the threaded part of the tap passes into the hole. Then reverse the direction of rotation and work two back and one forward, until the tap is eventually free of the hole. Sometimes the turning tap may become stiff and seem to resist movement. If this happens, work very slowly and carefully and never snatch at the tap, until it becomes easier again. As the tap cuts, a considerable amount of heat is generated, so you should dress it with a little light lubricating oil before inserting it into the work. This will keep it cool. This lubricant also performs another very important function. As the tap cuts, it actually removes metal in the form of swarf. With harder materials this swarf may be a coarse powder, rather like iron fillings. With softer materials (aluminum, plastics, etc.,) the swarf comes in a continuous strip or chip. The oil will help to keep the swarf moving away from the cutting place. If the swarf is allowed to interfere with the cutting process, the thread will be deformed and the work ruined. I usually blow briskly on the work from time to time, just to be sure. Do not forget to shut your eyes when you do this or it will be a hospital situation! Remember to keep the tap vertical and work slowly and carefully.
Each size of tap comes in a set of three, and these three must be run through the hole in the correct order:
- The first tap is a "pilot" or "leader" tap. It has a tapered end so it will settle into the appropriate position in the hole. The tapered end of the tap will cut a very shallow thread; it will be deepened to the full depth as the taper widens. It is this first tap which actually cuts the thread.
- The second tap is a "clearing" tap. This simply clears away any burr or phrase which may have resulted from the cutting process.
- The third tap is a finishing tap, which just puts a good surface on the floor and walls of the groove.
Often, from less well-equipped hardware stores or in cheaper tap sets, one or both of the final two taps will be omitted. However, if you do dispense with one of these operations, the bolt may not run smoothly in the hole.
Now you can find a suitable bolt and run it into the threaded hole. It should run in easily, but not have too much side play. The clearing tap has a shorter taper than the leader. The finishing tap is not tapered at all, so you can identify them tactually.
A die is used to cut a thread on a piece of rod, or on a virgin bolt.
A tapping-sized hole of relevant size is drilled and tapped in the center of a steel disc. The diameter of this disc may be several times as large as the center hole. Three or four equally distributed holes are cut from the center hole towards the outer edge. The disc will be about 1/4" thick. Around the outer edge there will be two or three small indentations to act as location points when securing the die in its holder. The die holder is known as a "stock."
The stock is a piece of mild steel whose outer diameter is larger than that of the die. It can be any symmetrical shape; most often, they are round. This steel disc will be about 3/8" thick. Handles protrude from opposite edges as they do on the tap holder.
A hole is machined in the stock which is large enough to accommodate the die, but this hole does not go clear through. Rather, this hole is about 1/4-inch deep; from here on, a smaller hole is made whose diameter is larger than any screw anticipated, but which will not let the die pass all the way through the stock. The result is a stepped hole. The die can sit comfortably on the step. There is a set screw in the outer rim on the stock; the die is oriented so the set screw will fall into a location point on the edge of the die.
When putting a thread on a virgin bolt, make the bolt secure in a vise, then locate the die (firmly held in its stock) on the end of the bolt. Apply the same techniques as if tapping. You do not have to use three dies as you did with the taps. The one die does the whole job.
The first couple of threads on either side of the die are slightly shallower than the rest so as to make it easier to get a cutting process started. Some dies are tapered; in this case, the side with the larger hole should be the one to face the end of the bolt first.
You can buy tap holders and die stocks ready-made, but if you feel adventurous enough to have a go at making your own, it is well within the capabilities of a modest machinist. At the other extreme, you can buy whole sets of taps, and whole sets of dies; these sets will come with appropriate tap holders and die stocks, along with adapters where needed. Such sets can be as much as several hundreds of pounds (or dollars), depending on their range of sizes.
Before the so-called industrial revolution in the 18th Century, the most common use of the screw was in coach building. Large screws were used to assemble the various parts of the vehicle. They had a fairly thick shank with a sharp pointed taper and a screw thread. They also had a square head. Screws of this type can still be found in some industrial installations. When we began to make machines, the need arose for something a bit more sophisticated. Over the years a few standard heads were evolved to fulfill particular purposes.
The so-called coach bolt (not to be confused with the coach screw), although originally used for the same purpose, has a threaded shank, but no taper. The head is shaped like a section of a sphere. A small part of the shank immediately under the head is made square. The width of this square is the same as that of the shank. The hole through which the bolt is to be passed is squared to receive this part of the bolt; this holds the bolt still while the nut is tightened. The head may not have any other arrangements for controlling it. You may occasionally find smaller versions of this in commercially made electrical equipment.
The types of heads you are likely to encounter are listed below.
- A popular form of bolt head is cylindrical in shape. [Editor's Note: This style is much more common in European equipment than in products of the U.S.]
- Another style includes those heads which are round on top. The standard "round head" is formed into one-third of a sphere.
A variation on this is the so-called "binder head;" this has a more gentle curvature, the head diameter is larger, and it often has a lower profile. (The binder head is most commonly found in electrical work, especially in screw terminals.) A flattened-looking binder head (still with beveled edges) is often found on "sheet metal screws;" this is called a "pan head," and the "binder head is sometimes misnamed "pan head."
- The third most common type of head is known as a "counter-sunk" head. The top of this head is often flat, but its underside is beveled down from the head size to the shank size. A special counter-sinking tool is required to shape the mouth of the hole to match the underside of the bolt head. When tightened, the head will lie flush with the surface of the work. Sometimes, a countersunk head will have a slight curvature on top; this is called an "oval head."
- The "counter-sinking" tool is readily available in hardware stores, and it is fairly easy to use--with a little practice. It can be driven by an electric hand drill. When purchasing one, the important parameter is that you get one which is larger than the head of the bolt; a 1/2- or 3/4-inch tool will be amply large for most applications.
- Another type is the "fillister head." Related to the cylindrical head (only smaller in diameter), this style is intended for holes which are "counter-bored;" the hole is enlarged to accommodate the head itself.
- Unlike with counter-sinking, creating a proper counter-bore in a hole requires a special drill bit (the type used on milling machines) which is flat on its end. The machinery used with this bit must be able to cope with the problem of properly locating the bit precisely over the hole. Use of an ordinary drill bit will create a counter-bore whose bottom is beveled; the result is that inordinate stress on the material will be applied when tightening the bolt.
- Finally, setscrews may have a variety of heads. They may be either knurled, or milled, or even have butterfly wings as the head. These arrangements are so that you can grip them between finger and thumb for tightening. Then again, a setscrew (sometimes called a "grub" screw) may be intended to disappear under the surface of the work into the hole. This type will, of course, have no head, though it will need to have some arrangement, a slot or a small socket, for driving it home.
There are many ways in which the head of the bolt is controlled while the nut is tightened. In the familiar method, a slot is cut across the top of the head, and the blade of a screwdriver is placed in this slot to hold the bolt still. The proper size of screwdriver is one whose blade is wide enough to span the entire width of the head (with perhaps a little blade to spare), yet one which is thin enough to reach bottom in the slot.
In the last three decades, another method of controlling the head has become popular. As a general category, this includes heads whose driving systems involve four contact points. The "cross-head" for example, can serve as a simple illustration. Instead of a single slot which extends right across the head, there is a cross (a second slot at right angles to the first, bisecting it at its center). The slots do not extend to the edge of the head. A special screw-driver is required.
The most commonly used is the "Philips-type" head. Still having four "flutes" around the screwdriver, the tool is pointed; this has an industrial advantage, since the driver finds its mark easily.
The list to follow correlates the Philips screwdriver shank size with the "number" (a size designation to be discussed later) of the screw:
Table I Philips Size vs. Screw Size
(The first number is the Philips bit size, after which is listed the screw sizes with which this bit is appropriate.)
- 1/8-inch: No. 0 and 1
- 3/16-inch: No.2, 3, and 4
- 1/4-inch: No.5, 6, 8, and 10
- 5/16-inch: No. 12, 1/4-inch, and 5/16-inch
- 3/8-inch: Use your imagination
There are variations on the Philips head which have a modified shape. One such is the "Frearson"--sometimes called "Reed and Prince;" these are just similar enough to cause you to use the wrong tool on them. Another variation is a standard set by the "ISO" (International Systems Organization).
Listing all of these is not possible, but be aware of their existence.
[The editor has long suspected that, since my Philips screwdrivers never fit them, the heads used in Japanese tape machines must be of a deviant type. I have had good results on these screws when I have ground off the point of my screwdriver; I have no Philips bits with their points intact, and I highly recommend this procedure. It works.]
Both screws and bolts are made with these types of heads. For best results, the correct size and type of screwdriver should be used, and this is particularly so in the case of the cross head. Also, with cross heads, you must keep the screwdriver at right angles to the head at all points. If you do not, you risk damage to the slots; and once this happens, the head will be difficult to control.
It is very frustrating to find that, because the slots are deformed, you cannot get a tight bolt undone. There are, of course, tricks which you can use to get round this problem, but we won't go into that at present. (The remedy usually involves an unpleasant process, such as drilling a hole down through the screw which accepts an "extractor" bit.)
The next class of head-controlling systems includes bolts that have sockets to be fitted with special wrenches. The most common of this type is the "Allen-head." The Allen wrench is a piece of hexagonal steel, one end of which is bent at right angles to afford a good controlling grip. The wrench is "measured" across opposite flat faces. The two popular styles of bolt are: the setscrew (which has no head), and the "cap screw" which has a cylindrical head. These sizes are tabulated as follows:
Allen Wrench VB. Screw Sizes
The first entry is the wrench size in inches--measured across opposite flat faces. The next listing is the appropriate "caphead" bolt size, followed by the size of the appropriate setscrew. A line of dashes indicates a missing entry--for example, a cap-head bolt may not exist for that particular wrench.
- 0.028-inch: ----; No.0 setscrew
- 0.035-inch: ----; No.1 and 2 setscrews
- 0.05-inch: No. 0 cap bolt; No. 3 and 4 setscrews
- 1/16-inch: No. 1 cap bolt; No. 5 and 6 setscrews
- 5/64-inch: No. 2 and 3 cap; No. 8 setscrew
- 3/32-inch: No. 4 and 5 cap; No. 10 setscrew
- 7/16-inch: No. 6 cap; ----
- 1/8-inch: ----; 1/4-inch setscrew
- 9/64-inch: No.8 cap; ----
- 5/32-inch: No. 10 cap; 5/16-inch setscrew
- 3/16-inch: 1/4-inch cap bolt; 3/8-inch setscrew
- 7/32-inch: ----; 7/16-inch setscrew
- 1/4-inch: 5/16-inch cap bolt; 1/2-inch setscrew
Here too, there are similar products. The most common variation is the multi-splined Bristol wrench. Made from a piece of steel with a right-angle bend in it, these feel similar to Allen wrenches. However, with a fingernail, you can feel that, instead of flat faces, there are "flutes" or ridges that run the length of the Bristol wrench. What's more, they come in four-flute and six-flute versions, just to keep life interesting.
[The editor has new hot information that there is yet another dad-ratted type that you are likely to encounter soon. Although designed for automotive use, it has now found its way into products of Tektronix and Apple. Called "Torx", it resembles a six-spline Bristol, except that the flutes are round, not square. The advantages are: Having splines, they are more durable than Allens. With the flutes being rounded off, it is possible to stamp out the screw heads, rather than machining them (which is absolutely necessary with Bristol heads). It's a good idea; I'm sure sorry somebody thought of it.]
There are other less common methods of controlling screws and bolts, but we cannot discuss them all. Many have been invented for the automotive industry, and there is where you'll find them.
To install a specific bolt in a tapped hole, you need two drill bits, a set of three taps, an appropriate washer and a suitable screwdriver. The tables at the end of this article will give the necessary information. If your fixture is to use a nut and bolt, you only need one drill bit.
We now come to the question of threads. My remarks must again be very sketchy, but you may find the tables at the end of this paper helpful.
As already mentioned, there are numerous different types of thread, to say nothing of the ones which are specific to the large manufacturing companies. When replacing a missing nut or bolt, you may find that the easiest thing to do is retap the hole. You will often find the size of the hole is such that you can run the narrowest-sized standard tap or die through, and use a standard
thread. This procedure is made easier by the fact that industrial threads are generally cut shallower than standard ones.
Given the size of the rod or hole, the parameters which will interest you are: 1) the number of threads per inch (TPI); 2) the angle of the thread; 3) the type of thread; and, 4) the depth of the thread.
The number of threads per inch means just what it says. The more threads there are to the inch, the more slowly the nut will climb up the bolt.
The angle of thread is a little more complicated. The kind of threads you are most likely to come into contact with have a standard spiral. They begin to climb from the outset, like a spiral staircase.
In domestic gas and water (and in some central heating and refrigerator installations), for example, a so-called parallel thread is used. In this case, the first thread stays the same distance from the end of the bolt for the whole of the full turn; the spiral is established by making the wall of the groove rather thin to start with, getting thicker as you go round. After the first circuit, the walls stay at a constant thickness.
The type of thread must be specified when buying nuts and bolts, taps and dies. This thread type refers to a number of combinations of the other parameters, as you will see from the tables (note the differences in tapping-sized drills).
The depth of the thread refers to the extent to which the thread cuts into the metal.
There are other important features which are characteristic of each type of thread. Some have flat tops to the ridges between the grooves, some have rounded tops, some have sharp peaks. When you select the type of thread, the shape of these ridges is implied. The above points also apply to the floor of the groove. It is because of the different combinations of these various parameters that, when trying a nut on a bolt, you may find that it seems to run OK at first, and then begins to become stiff. This is because the threads are not quite of the same type.
The tables with which we are concerned can have eight or more columns of figures, each referring to a specific parameter. This provides a great many combinations, so you will see we can barely scratch the surface of the subject in this paper.
The three thread types which are likely to be relevant to you are:
- Machine Screw types
We shall not provide all the eight columns, as some of them are only of interest to the manufacturers of taps and dies. We shall concern ourselves with four or five parameters only. These are:
- tap size
- the number of threads per inch (TPI)
- outside diameter of bolt
- tapping sized drill
- clearance sized drill
Further details of these are given in the preamble to each table.
Sometimes you will need to know the TPI. If you wish to tap a hole in a piece of metal (say, 1/16" thick), you need to have enough threads in the hole to hold the bolt. If you cannot get enough threads, you would be advised to use a self-tapper instead.
The tapping-sized drill is used if you wish to cut a thread on the inside of the hole to receive a bolt. The clearance-sized drill is used if you want a bolt to pass easily through the hole without having to screw it in.
The full table would cover a range of purposes from about 1/25 inch to about 2 inches. We shall only provide a section of the table covering the range from about 0.1 inch to about 0.5 inch. Anything smaller or larger than this would probably not concern the electronic experimenter.
Here is a bit of throw-away information: To convert inches to millimeters, multiply by 25.4. To convert millimeters to inches, divide by this figure.
Table III--ISO (International Systems Organization)
This method, of expressing the sizes of taps and dies, nuts, bolts and drills is in general use by multinational companies who are engaged in industries such as electronics, aircraft, automobile, etc. throughout the world.
The TPI is not given directly. Instead, the "pitch" is specified (the TPI is the reciprocal of the pitch). For example, looking at the table, we see that, with a tap size of number 4, the pitch is 0.7. All the figures for this first table are in metric measure. This pitch figure is 0.7mm, so we must first convert it to decimal inches. 0.7 divided by 25.4 equals 0.27559. The reciprocal of 0.27559 is 36.28, and this is the TPI.
In this table, the figures are given in the following order:
Tap Size (in millimeters), Thread Pitch (millimeters per thread), Tapping-Sized Drill (in millimeters), and Clearance-Sized Drill (in millimeters).
- 2.5mm: 0.45; 2.05; 2.6.
- 3mm: 0.5; 2.5; 3.1.
- 3.5mm: 0.6; 2.9; 3.6.
- 4 mm : 0.7; 3.3; 4.1.
- 4.5mm: 0.75; 3.7; 4.6.
- 5mm: 0.8; 4.2; 5.1.
- 6 mm: 1.0; 5.0; 6.1.
- 7mm: 1.1; 6.2; 7.2.
- 8mm: 1.25; 6.8; 8.2.
- 9mm: 1.3; 7.8; 9.2.
- 10mm: 1.5; 8.5; 10.2.
- 11mm: 1.6; 9.5; 11.2.
- 12mm: 1.75; 10.2; 12.2.
- 14mm: 2.0; 12.0; 14.5.
Table IV--ANF (American National Fine)
In this table, the TPI is given directly; there is no juggling to be done. The tap number, which is also the screw number, is the first column. To begin with, these are just numbers, but as the size increases, the figures in, this first column change into fractions of an inch.
The drill sizes are in metric measure (mm).
In this table, the figures are given in the following order:
Tap Number or Size in Inches, Threads per Inch (TPI), Tapping-Sized Drill (in millimeters), and Clearance-Sized Drill (in millimeters).
- No.3: 56; 2.15; 2.65.
- No.4: 48; 2.4; 2.95.
- No.5: 44; 2.7; 3.3.
- No. 6: 40; 2.95; 3.6.
- No.8: 36; 3.5; 4.3.
- No. 10: 32; 4.1; 4.9.
- No. 12: 28; 4.7; 5.6.
- 1/4-inch: 26; 5.5; 6.5.
- 5/16-inch: 24; 6.9; 8.1.
- 3/8-inch: 22; 8.5 ; 9.7.
- 7/16-inch: 20; 9.9; 11.3.
- 1/2-inch: 18; 11.5; 13.
Table V Machine Screw Types
In this table, there are alternative TPI's for some screw numbers. Once the screw size has been stated in the first column, it will not be repeated for the alternatives, and this column will be left open until the screw number changes.
There are five columns in this table; the figures are given in the following order:
Tap or Screw Size (just a number), Threads per Inch (TPI), Bolt Diameter (in inches), Tapping-Sized Drill Number, and Clearance-Sized Drill Number. (Note that these drills are not given dimensions in many cases; they are available by number or letter. The drill numbers go down as the bits get larger, while the letters work the other way round.)
- No.3: 48; 0.099; 47; 45.
- 56; 0.99; 45; 44.
- No.4: 32; 0.112; 45; 43.
- 36; 0.112; 44; 42.
- 40; 0.112; 43; 40.
- 48; 0.112; 42; 40.
- No.5: 36; 0.125; 40; 38.
- 40; 0.125; 38; 36.
- 44; 0.125; 37; 35.
- No.6: 32; 0.138; 36; 33.
- 36; 0.138; 34; 32.
- 40; 0.138; 33; 31.
- No.7: 30; 0.151; 31; 29.
- 32; 0.151; 31; 29.
- 36; 0.151; 1/8-inch; 29.
- No.8: 30; 0.164; 30; 28;.
- 32; 0.164; 29; 27.
- 36; 0.164; 29; 27.
- 40; 0.164; 28; 26.
- No.9: 24; 0.177; 29; 27.
- 30; 0.177; 27; 25.
- 32; 0.177; 26; 24.
- No. 10: 24; 0.190; 25; 23.
- 28; 0.190; 23; 21.
- 30; 0.190; 22; 20.
- 32; 0.190; 21; 18.
- No. 12: 24; 0.216; 16; 14.
- 28; 0.216; 14; 12.
- 32; 0.216; 13; 11.
- No. 14: 20; 0.242; 10; 8.
- 24; 0.242; 7; 5.
- No. 16: 18; 0.268; 3; 2.
- 20; 0.268; 7/32-inch; 9/32-inch.
- 22; 0.268; 2; B.
- No. 18: 18; 0.294; B; D.
- 20; 0.294; D; G.
- No. 20: 16; 0.320; G; 17/64-inch.
- 18; 0.320; 17/64-inch; I.
- 20; 0.320; I; 9/32-inch.
- No. 22: 16; 0.346; 9/32-inch; L.
- 18; 0.346; L; 5/16-inch.
- No. 24: 16; 0.42; 5/16-inch; O.
- 18; 0.342; 0; 21/64-inch.
- No. 26: 14; 0.398; 21/64-inch; R.
- 16; 0.398; R; T.
- No. 28: 14; 0.424; T; 23/64-inch.
- 16; 0.424; 23/64-inch; V.
- No. 30: 14; 0.450; V; 25/64-inch.
- 16; 0.450; 25/64-inch; 28/64-inch.
In the systems of Tables IV and V, the type of bolt is specified by two parameters (aside from the head style and length). A No.6
bolt with 32 threads per inch is called a "6-32 machine screw or bolt." A No. 10 bolt having 24 threads per inch is called "10-24."
The book which was used to verify the figures in this paper is "Machinery's Handbook," by Erich Oberg and F.D. Jones, published by the Industrial Press, 148 Lafayette Street, New York, NY.
Limited space has dictated that I leave out a great deal of detail. If anyone would like to raise any questions with me, they will be welcome. My address can be obtained from our editor.
[While its author says there is much left out of this paper, the information herein is as much as you'll find in an electronics lab the size of mine at Smith-Kettlewell. The tap and die sets have abbreviated tables like the ones here, and the drill index has abbreviated tables as well. About the only things left out of importance are general statements as to where you will find such a thing as a No.5 machine screw with 36 threads per inch, for example. I will throw a few things in here as follows.
To put things in perspective, youngsters' Erector sets and Mechano sets use 1/4-inch long round-headed 8-32 bolts, with 6-32 bolts being used as setscrews. The 8-32's are just a little fatter than 1/8-inch; the holes that accommodate them also allow 1/8-inch shafting to turn easily.
The most common nuts and bolts in non-metric sizes (which you will find in electronics assemblies) are: No.4, No.6, No. 8, and an occasional No. 10 (holding down a transformer or something). For some reason, although 4-36's are very common outside the electronics field, No. 4 screws usually have 40 threads per inch in electronic stuff. All other nuts and bolts will have 32 threads per inch--6-32, 8-32, and 10-32.
Also for unknown reasons, except that they look a little nicer, binder-head screws are most prevalent in electronics, even when they are not screw terminals. This makes replacement a bit tricky, since they must be ordered from mail-order houses; they are not available in hardware stores.
Screw terminals always have an oddball thread. The most common Cinch-Jones barrier strip (the kind you can buy at Radio Shack) uses 5-36 binder-heads. The best reason for doing this is that, when you lose one, you get to buy a whole new barrier strip (or re-tap the blamed thing for 6-32).
As far as setscrews in control knobs are concerned, 4-40's with Allen heads are used in small ones, while 6-32 and 8-32 setscrews will be found with equal occurrence in larger knobs. Just to be nice, the larger sizes may have slotted heads -- then again, they may not.
The best way to identify the kinds of head-controlling systems is with the point of a braille stylus. With this magic instrument, you can explore the head for a slot or a dimple; when it has a dimple, you can then count the contact points by tracing the parameter. Followed by educated guessing, you can save mountains of time identifying them.
Apparently by manufacturers' whim, the specified length of a bolt may include the head. This is often done with flat-head screws and bolts, but this dubious practice can surprise you elsewhere.
Bolts, nuts, and woodscrews, as bought from neighborhood hardware stores, are usually made of steel, often plated with cadmium. On the other hand, nuts and bolts used in electrical stuff are made of brass. Likewise, wood screws in pianos are brass. This is important to know for the blind technician, since these two materials look very different; a project will not look professionally done unless the screws match. The way to find out is to test them with a magnet.
The lockwashers found in electronics are often not of the usual style. Rather, washers called "star washers" are more common. These are made of thin spring steel, and they have scallops cut around the edge; these "scallops" are then bent in opposite directions to form a washer whose edge feels very jagged. They come in both "inside star" and "outside star" configurations; the "outside star" washers are best for holding a nut still while the bolt is being tightened.
When installing a star washer, put it between the surfaces that you want to keep from moving. For example, pots and switches often come with star washers. A common mistake is to put the bushing through the panel first--then adding the star washer and nut. This is a silly practice. You don't want to keep the nut still and allow the control to turn; put the star washer on the control first, so that it holds the component still and prevents it from coming loose.
Well, hurrah for the Technical File, and our thanks to Albert Yeo. If I had had this information in braille when I first went to work, I would have been more independent, and there would have been fewer broken taps to explain to my supervisor.
While all of these sources are good, there is one item worth specific mention. Digi-Key Corp. sells "electronics hardware kits;" these are assortments of screws, nuts, and lockwashers. The 1600-KIT has hundreds of screws in various lengths, covering sizes 2, 4, 6, and 8; it sells for about $15. The 1601-KIT has larger bolts, covering sizes 6, 8, and 10; this is $23. Foreign orders are accepted with an extra $5 charge.
- Digi-Key Corp., P.O. Box 677, Thief River Falls, MN 56701
- Jensen Tools, Inc., 7815 South 46th Street, Phoenix, AZ 85040
- Small Parts, Inc., 6901 North East 3rd Avenue, Miami, FL 33138
- Techni-Tool, P.O. Box 368, Plymouth Meeting, PA 19462
The method of resistance soldering works by passing extremely high current through work pieces (the connection being soldered, not the components); the work pieces then become heated and act as their own soldering iron. The tool consists of either a pair of electrodes, or a single electrode associated with a ground-return clamp. These tools are sources of electric current, not sources of heat.
The resistance-soldering tool does not heat up and stay hot. The only heat energy it absorbs is transferred to it from the connection, and, unlike conventional irons, this transfer of heat to the tool is not very efficient, since the tool is not in a molecularly bonded solution of solder with the work. Therefore, the tool generally gets cool enough to touch very soon after a connection has been made. This has great appeal to some blind users; they position the tool and the solder with their fingers, and then they press a foot switch to initiate current flow.
You ask, "Why didn't you tell me that there was a perfectly safe way to solder, before you wrote hundreds of pages on lethal hot irons?" (The author has been criticized by three readers who are dyed-in-the-wool proponents of resistance soldering.) My answer is that things are not always as simple as they seem; there are major pitfalls which must be reckoned with. In fact, my respect for resistance soldering as a viable technique came not from my own experience, but from seeing some top-notch work being done in the laboratory of Rick Joy, a deaf-blind reader of SKTF.
Manufacturers' advertisements tout that, "This method allows connections to be made more quickly, so that heat won't be transferred to nearby components and to insulation which might otherwise melt!" "Quickly" is an undisputed truth--and at least one manufacturer, American Beauty, is honest enough to include the statement, "The eye is generally the best judge of when to remove the tool." I'll "second" that statement! The only limit to the temperature a connection can reach is its ability to dissipate power--the temperature can go sky-high very quickly.
My first casual experiments with this method were disastrous. I would, in my usual style, nonchalantly feel about the connection with the solder; when it melted, I withdrew the solder and then withdrew the soldering tool. More than once, I would find that as much as an inch or so of insulation had vaporized along adjoining wires--that's getting hot. (The literature suggests that you can also use this equipment to anneal and to temper metal parts--that's hot!)
American Beauty suggests that, before you use the equipment on actual work, you try several power settings on similar scrap work pieces. All the manufacturers recommend their equipment chiefly for assembly-line soldering, where the equipment can be preset for one size of joint.
Recognize also that there are electrical risks involved with resistance soldering. If, for some reason, good contact between wires at the joint is not established, you can inadvertently put components in series between the electrodes of the tool; this can test your smoke alarm systems and set the neighbors to wondering what you're cooking in there. It pays to know a little electrical theory and to use good judgment when you place the electrodes on the work. (These devices are powered by low-voltage, high-current transformers; the current supplied to the electrodes is therefore AC.) Problems can sometimes be eliminated by heating only one item of - the work pieces. If you heat one item, pick the one of largest heat capacity-the biggest piece of metal.
Finally, you can only solder stranded wire if it has been pretinned--otherwise, you might burn up a strand or two, and never have an effective "soldering iron" (the soldering iron being comprised of the work itself). Of course, this raises the question of the tool's effectiveness in tinning stranded wire, a necessary operation in all electronics work. Therefore, you might well consider keeping an "instant-heat, fast-cooling" gun or "cordless" iron on the premises for just this task. (A discussion of guns and cordless irons appeared in "Soldering--Part I," SKTF, Fall 1980.)
All in all, however, "resistance soldering" is a legitimate alternative for the blind technician. Though the above remarks may seem skeptical, most of the questions will find adequate answers in the discussion to follow.
General Description of Tools
Three common styles of tools are readily available. They are described as follows:
The classic electrode configuration is a single rod, traditionally made of carbon, but nowadays often made of an alloy of metals. Along with this is a "ground-return clamp" which is attached to one of the work pieces a little ways away from the connection. This configuration is very good for large items of high heat capacity. Carbon has the advantage that it can tolerate higher temperatures, while metal has greater tensile strength.
Another configuration is to have two electrodes, mounted in a "fork" with a fixed spacing, which can be adjusted (by bending or grinding) to fit a particular job. This style is often used in assembly-line
settings. On the other hand, PC-board connections are just standard enough to make this the instrument of choice for doing this kind of work.
The style of most interest to us is the tweezer-type tool. This consists of two pointed electrodes (made of some metal alloy which does not take solder) mounted in a spring-loaded insulating handle. This device, though limited in the size of work it can accommodate, can handle most any of the commonly found electronic connections.
(These can be gotten in large enough sizes to solder 14-gauge wire, for example, or small enough for wire of less than 50-gauge.)
All of the above configurations are available in extreme variations, if you jump from one manufacturer to another. For example, the Hot Tip company makes very small single-electrode probes. Other companies make a "plier-type" tool which has carbon blocks for jaws--you can temper steel with those things. Yet another style is a panel containing electrodes--this panel being mounted directly onto the power transformer.
Power Transformer Types
The power transformers are either multi-tapped or variable types; they are good for 100 watts or
greater. Their on-off switch is usually something separate. Most often, you buy a foot switch which has a piggyback AC plug and socket at the end of its cable; the transformer plugs into this receptacle. On the other hand, American Beauty sells a series of units which are controlled from a separate connector on the "power unit;" this facilitates the option of having a pushbutton on the handle of the soldering tool.
An embellishment is to add a timer which shuts the power off after a preset period. The American Beauty literature cautions that this is not a recommended feature where variations in the size of work pieces are expected.
Resistance soldering equipment is often used with pre-formed units of solder; they may be in the shape of balls, beads, or tiny washers--with or without flux. These "solder preforms" are marvelous for industrial applications on an assembly line; you just slip them over a lead, place the tool on the work, and press the foot control.
Use of solder preforms takes away an important source of feedback for a blind technician. Now that you are not holding onto the solder, how will you know when it melts? It may be possible to depend on alternative cues. (The following tips refer to "Tactile Feedback" as discussed in "Soldering--Part II," SKTF, Winter 1981.)
Looking for a sharp rise in temperature of an adjoining component lead may still work, but only if the lead you are feeling is not one being electrically heated by the tool. If you are sure that the lead you are monitoring is not being directly heated by the tool, a sharp temperature rise will probably mean that wetting of this lead has occurred.
The "squeakiness" of solder-wet metals (when subjected to slight motion) will always tell the story. However, this squeakiness
will not be as apparent through the resistance-soldering tool as it is through
the conventional iron. This is true because the electrodes of the resistance-soldering tool are never "wet" themselves.
Finally, solder preforms are usually miniscule in size; fitting them in place is not easy. I prefer to hook the solder around a lead (3/4 of a turn being enough for small socket pins in a PC board), and this puts me back in the position of being able to monitor the solder flow directly.
Selection of Equipment
Everyone agrees that "trial and error" (or perhaps having a "sales consultant" drop by) is the way to decide which setup best suits your application. It's not quite as bad as all that--you can make a good guess from the tools listed here.
If you're going to err, do it on the large side. For example, if you are going to solder house wiring; get the largest tweezers you can find, a single electrode of perhaps 1/4 inch diameter, and a power transformer of 250 watts. If you are interested in soldering point-to-point wiring on perforated board, whether IC's are involved or not, tweezers whose electrodes are pointed and whose shank diameters range from 0.04 to 0.08 inches will do fine, and the power transformer need only be good for 100 watts.
A continuously variable transformer may be a convenience; then again, it means that tried-and-true settings will be harder to repeat exactly. The variable transformers are a nicety where fine control over a particular industrial operation is being set up. Your work may involve a variety of work sizes; close monitoring of melting of the solder will be necessary anyhow, so why not make do with a less expensive multi-tapped unit.
Stated more than once in the American Beauty book, "The Principles of Resistance Soldering," initial setup of the equipment will necessitate a trial-and-error process. It is for this reason that this paper cannot say specific things like, "Set the PDQ-5 power supply to position 3, and so forth. Students of this series of articles know enough about the metallurgy of soldering to do educated experimentation on their own--say yes. The basic steps are:
- Set the transformer for a setting suitable for the job (based on your experience and by making an educated guess.)
- Place the solder on the work in such a way that you can judiciously monitor its status; you will want to know, with certainty, when it melts. Wrapping the connection with a measured amount is one method; you can then monitor the solder by pulling on it slightly. Then again, some people like to feed solder when the time comes (this takes less setup time); in this case, keep it against the connection and press forward gently.
- Place the electrodes on the connection with the power off (doing so with the power on will cause impressive arcing).
- Close the power switch (be it a foot control or a pushbutton on the soldering tool).
- Watch that solder like a hawk; put
enough tension on it so that you will know
immediately when it melts. If a pre-
determined amount has not been wrapped around the connection, apply an appropriate amount-and be quick about it!
- Simultaneously release the switch, remove the tool and the solder.
- Modify the transformer setting as necessary, based on the previous similar connection.
If you can pass current through all the connecting work pieces (and if they are all of reasonable size), everything will get hot enough to take solder. However, this does increase the chance that you might pass current through circuit elements and not through the connection--if the items are not in firm contact, etc. You can heat the largest item at the joint and make this your "soldering iron" (instead of the whole collection of items). If you do the latter, wetting of all metals will not occur simultaneously; firm contact between the pieces is again necessary in order to promote rapid heat transfer to them all.
In choosing the "correct" heat setting, all of the literature specifically says to
"choose the highest setting which the operator can control effectively." I prefer to interpret this statement loosely; if taming the system down a bit means that I have enough time to make a decision or two during the process, I'll do it that way. Remember, these tools are intended to be sold to assembly-line shops; they want to keep the times minimal.
I would think that turning up the heat would have diminishing returns. Nowadays, the solder we use often contains so-called "activated flux." According to the Kester soldering manual, "activated fluxes," when compared to the most basic rosin flux of yesteryear, have inferior breakdown characteristics in the presence of excessive heat.
On the other hand, setting the heat too low carries its own set of risks. As with any soldering, too small an iron or too little heat will allow a damaging amount of heat to be imparted to connected components before the joint reaches soldering temperature. Given the wrong conditions--poor lead and electrode placement--these ill effects could be magnified with resistance soldering. The energy to one item could be terrific, enough to damage this component, but not enough to heat its neighboring leads at the joint.
I love this section in books. "Make sure the power setting is correct, and make sure all connections are secure." Of course, all that stuff works, or you wouldn't be reading the book.
American Beauty suggests that the electrodes could have gotten dirty--coated with flux or with oxides. With their units (which have solid alloy electrodes; i.e., no plating), they recommend that you clean them with a strip of emery paper or a small wire brush. Not knowing all the variations you may run into, as far as electrode materials are concerned, I would have to advocate reading the instructions of your particular tool.
I have seen one interesting problem with a set of Hot-Tip tweezers which were not working. The electrodes had bent so that the chucks that held them were shorting ahead of the connection; installing heat-shrinkable tubing around one of the chucks would prevent this from ever happening.
Sorry, my direct experience with these devices is so old that I would not feel comfortable in recommending anyone product specifically. I can outline (basically restate) principles discussed earlier, so that you know what to watch for. Meanwhile, price is not much of a factor; everybody, except for Teledyne Kinetics, wants from between $100 and $120 for a setup (by the time you get a foot control and such).
Of the three users I have interviewed on the matter, two use "tweezer-type" instruments. Tim Cranmer, on the other hand; has used a single-electrode device to heat the posts of wire-wrap IC sockets, around which he would wrap the wires being attached (just one turn around the post), then wrapping solder around the post further up. There are a couple of single-electrode units small enough to permit this, and they are listed here. Remember, you can buy one power unit (and an accompanying foot control if it is not included)--then pick an array of hand pieces, including both tweezers and single-electrode holders. (Of course, all single-electrode assemblies come with the necessary "ground clamp" which serves as the return
All of the advertisements are misleading when they speak of "precise temperature control" and "no heat being transferred to adjacent components." What they really mean is that, given a particular repeatable situation, you can set up the equipment for--and get the operator used to--a given solder connection, and make the connection efficiently enough to protect nearby components.
They all refer to their adjustable power supplies as having something to do with "temperature control," which is true, only indirectly. One manufacturer called their power supply "a solid-state temperature controller;" right away I jumped for joy. Could this mean that they sense the temperature of the connection and thus control the temperature? Nah, it's just a transformerless variable power unit which is small enough to plug into the wall directly.
If the marketing jesters were forced to study engineering (thus spending a short while in a "Control Systems" class), they would learn that the only systems that you can really call" "controlled" are ones which have corrective feedback. "Open-loop" systems have adjustments; one can adjust them so that, all things remaining constant, the resultant "control" over their operation will be predictable. Open-loop systems, however, are not controlled, in the true sense of the word.
What you need to do is, by experiment, set up the variable power supply so that a solder connection can be made in a reasonable time--in a range of perhaps 2 to 7 seconds. This "control" will change for every piece of work you're doing.
American Beauty (American Electric Heater Co.)*
For each hand piece, a "power rating" is listed. This indicates with which power unit the tool is to be fitted. It does not indicate the power delivered to the work; this cannot easily be determined, since every item has its own current density and resistance.
Note that the foot control comes separately from the power unit. Although this is not true of other manufacturers, the prices of the eventual setups are still quite competitive.
- 10552--5/64-inch metal electrode (stainless steel), 15 to 100 watt
- 1015--3/32-inch carbon, 15 to 100 watt
- 10572--1/8-inch carbon, 15 to 100 watt
- 10573--3/16-inch carbon, 15 to 250 watt
- 10511--(said to be "standard" for general electrical work) 1/4-inch carbon, 85 to 350 watt
- 10510--adaptor to convert 10511 hand piece for 3/8-inch carbon, tip no. 10527)
- 10522--bushing to convert 19511 to 3/16 carbon, tip no. 10525
Tweezer-type Hand Pieces:
- 105133--"Microtweezer" uses 0.040 inch diameter "chromel" wire electrodes, 15 to 100 watt, electrodes replaced with 105134 tips
- 10541--opens to 3/8-inch, 0.078 inch diameter stainless-steel electrodes (ground to a point), 15 to 100 watt
- 105127--opens to 1/2-inch, uses 1/8-inch diameter stainless-steel electrodes (ground down to blunt point), 15 to 250 watt
[The editor would start with the 10541 tweezers, with the possible addition of the 10552 and 1(3572 single-electrode hand pieces.]
(add suffix of 220/240V for these voltages):
- 105-A1--Three taps, 15, 50, and 100 watt
- 105-A2--Four taps, 85, 130, 185, 250 watt
- 105-A3--Continuously variable, 0 to 100 watt
- 10519--Has standard AC plug and socket on the end of cable
Single-Electrode Hand Piece:
- P-40--Typically used with 5/32-inch diameter copper-clad carbon electrode, for use with H-101A and H-202 power transformers
- P-8--For use with above P-40, this is a 0.040 inch diameter tungsten electrode which has been pressed into a 5/32-inch brass
- P-9--For use with the above P-40, this is a 0.060 tungsten electrode which has been pressed into a 5/32-inch brass adapter
Tweezer-type Hand Pieces:
- T-10S--"Standard tool" uses 0.040 inch diameter tungsten (type TT-2) tips, for use with H-101A power transformer
- TC-10S--Same as T-10S but with extra cork insulation for high duty-cycle applications
- T-10SA--For use with TT-2A "Nichrothol" which are easily shapeable, use with
- H-101A power transformer
- T-10S4--Uses "rigid" 0.060 inch diameter tungsten tips (type TT-4), for use with H-202 power transformer
- TT-10S4A--Used with easily shapeable "Nichrothol" tips (type TT-4A), for use with H-101A and H-202 power transformers
(120V 50/60 cycles shown in U.S. Catalogues):
(Note: The foot switch apparently comes with these power units.)
- H-101A--Has 5-position rotary switch, can deliver up to 200 watts (50% duty cycle); position 1 good for soldering 52-gauge wire, with position 5 good for soldering two 14-gauge wires.
- H-202--Has 5-position rotary switch; starts with position 4 of H-101A, capable of approximately twice the power.
[The editor would start with the T-10S tweezers, and possibly include the P-40 probe. The H-191A transformer has enough power for anything I would be doing.]
These are basically self-contained; there is no power transformer on the bench. The RSC-1 ($85) has a solid-state variable supply that plugs into the wall. The RS-1 is simpler ($60); they don't say how this one
is powered. Neither have foot controls. Rather, they seem to have a pushbutton control. They don't say whether the pushbutton also controls closing of the tweezer noses, but it sort of looks like that from the pictures.
- RS-1--Self-contained unit with tungsten electrodes
- RSC-1--Heat is controlled from a solid-state, plug-in unit; has tungsten electrodes
This device is a unit out of which protrudes electrodes that look like square long-nosed pliers. It has a trigger that serves two functions: a slight pressure closes the points. Additional pressure turns on the power.
Square carbon tips are standard. However, small-diameter "special metal tips" can be gotten which are mounted into appropriate adapters.
The power transformer has two taps, high and low.
- Model J--Whole setup with carbon electrodes
- TLT--Is just the "Pres-to-Heat" hand tool
(I give you this, since you could probably adapt it for use with other power supplies).
- 1-0397--Replaceable carbon tips
- 1-2177--1/16-inch metal electrode, two of which are required.
- 1-2249--You need two of these adapters for above electrodes.
Suppliers and Manufacturers
788 Palomar Avenue Sunnyvale, CA 94086 (408) 739-8720
Macdonald 1736 Standard Street
Glendale, CA 91201 (800)423-2453 (Outside CA)
American Electrical Heater Co. (American Beauty)
6110 Cass Street
Detroit, MI 48202 (313) 875-2505
Triton Manufacturing Co., Inc. East Haddam, CT 06423
6 Elm Avenue
Hudson, NH 03051 (603) 883-7708
410 S. Cedros Avenue
Solana Beach, CA 92075 (619) 755-1187
by Frank Jeanmonod, G3JYT Pinner, Middx., England
I have used this guide successfully for many years; it works very well on the pins of IC chips, as well as for soldering larger connections. (I use a small Weller iron for the IC projects.)
The basis of this tool is a darning needle (which we call a "bodkin"). The handle is made from a bit of 3/4-inch doweling. I
drill a tiny hole in one end and ram the bodkin into the hole so that the pointed end protrudes about 2-1/2 inches.
Though not sharp, the point is such that when the tool is braced against the connection, the darning needle tends to stay in position. These needles are stainless steel, so solder does not adhere to them.
I first wrap solder around the bodkin--2, 3, or 4 turns, depending on the connection--, after which I locate the joint with its pointed end. Then, I slide the solder down the bodkin so that it contacts the work.
The bodkin is easy to find with the hot soldering iron; I then slide the iron down to the work.
[Editor's Comments: Well now, we have another good inventor in our midst. This tool has one distinct advantage over the tubular guide (SKTF, Spring 1983); this guide will never clog up. It has the disadvantage that you can no longer monitor the melting of the solder, which is ordinarily the main cue that the connection is hot enough. However, you still get other indications: Small motions of the iron against the work will
feel (and sound) "squeaky" when the flux has done its cleaning job. The smell of flux will be apparent. The adjoining leads and components will exhibit a sharp rise in temperature as the solder-wet pieces promote efficient heat transfer. Bravo, and thank you, Mr. Jeanmonod.]
by William A. Gerrey
[I guess I'd better break with my tradition and sign this article, since it's full of opinions.]
Abstract--This paper describes how I handled the various processes of engineering school. It shows, also, that there are compromises in "direct accessibility" which can be made in the interest of efficiency; no one need go without an education for the want of cart-fulls of special devices.
My formal schooling took place at California State Polytechnic University, where I received a Bachelor's degree in "Electronics Engineering" in 1971.
I had a good head start before I got there, however; my father, who was also blind, was very interested in radio and recording machines (from a user's point of view, not as a repairman or electronics hobbyist). Even though he never had one himself, he encouraged me to get a ham-radio license, which I did in 1960.
Both of my parents were very generous with "bucks for projects." They made sure that I got the basic tools--a multimeter, good soldering equipment and hand tools. Most important of all, in this learning process, they never placed dollar figures or quick judgments on the damage I did in "fixing things." (I returned their respect for me by taking this damage a little bit seriously; I didn't do it on purpose.)
Finally, my father was an avid fan of "The Braille Technical Press" (even though he only read about 2% of them). When I was too young to read, he read the advertisements and simpler articles to me.
The point here, however, is not to paint a portrait of myself and my "advantaged" career. Rather, it is hoped that a paper like this can be the necessary addendum to "good study habits"--an addendum many blind people do not get from their counselors and teachers.
Actually, this paper is born out of frustration. I have seen several students in programs from which they are partially excluded; this can be so extreme as to keep them out of the laboratories altogether. I have seen prospective students turned away from technology by both teachers and counselors. I have lived to see the day when a ham-radio license means less as a credential to blind license holders than it is for their sighted counterparts; "Oh you don't have to
learn this circuit stuff." It is mentally unhealthy to acquiesce to these views, and it is self-limiting to "accept our position," as some would define it for us.
Exemplary frustrating cases come to me from time to time, not only because I am someone people know who took on these problems, but because it is often hoped that I can solve the many obstacles through dazzling technical wizardry. More than once, a counselor sends his "client" to me, and he says, "Now, all I need is braille meters on these 15 or 20 instruments, and I'll be able to start school next semester." He needs every single one?
I've been through school, and I know enough to ask, "Who says that you need to have complete independence with all these instruments, your instructor?" The answer is invariably yes. He is to do the lab work all by himself. "How do the other students work, in groups?"
"Why yes, but my instructor says he wants me to work independently so that I won't hold back the team" he innocently replies.
Ahah! there's the crux of the problem. He is being taken out of his rightful place on a team to which he could contribute constructively, and he is put in the unlikely position of working and learning in the closet. It is at this point that our composite hypothetical friend gets a lecture on "Constructive Independence" from me; it is that lecture which comprises this paper.
A Case Study of Constructive Independence
I chose Cal. Poly because of their advertised emphasis on lab work. At the time, I had no idea how hard this is on a student; each lab only counted for one unit of lecture--even though each one took three hours--and you can soon find yourself out of time in the evenings. However, I have a fetish for the practical world.
My first inclination was to dazzle colleagues and professors with my various auditory instruments in the lab (some of these devices are commercially available, by the way). However, I soon learned that as a member of a lab team--usually comprised of three students--I could become a sought-after partner by exercising my talents where they could be most efficient. I became known for my preparedness, my ability to set up the experiments, and for my assistance in recordkeeping.
Instead of measuring instruments, I brought my portable typewriter to the lab. Whereas other lab teams spent perhaps half-of their time collecting data--each member looking at the instruments and writing down the numbers in his individual notebook--I arranged a collaborative situation wherein one member took measurements, I then tabulated them on my typewriter using carbon paper (meaning
that we all ended up with a copy), and the third member marked and drew graphs directly using carbon paper to generate graphs for all
of us. In the left-over time, I would have them draw raised-line versions of the graphs on a "Raised-Line Drawing Kit" (available from American Foundation for the Blind). Their "help" to me in the end was a blessing in disguise; the discussion which ensued over the raised-line drawings assured a better understanding of the work than was gotten by other students who had less time for discussion.
Since it was important to me to do so, I was always well prepared for the labs; I would do the setting up while my partners were doing a late reading of the material. If I didn't understand the setup from reading the preliminary sheets, I would go into the preceding class and look at their equipment.
If lab work had to be done independently, I would hire a fellow student (preferably one who also needed to do the work) as a "reader" (there being a State fund for such purposes).
The same techniques made me as welcome in chemistry and physics labs as they did in electronics. The point is, I took on responsibilities and used my talents as effectively as I could in order that asking for "help" could be done gracefully--without being invasive. The burden to do this was mine--not the teacher's, and not the students'.
"But what," you ask, "if there is no team work?" First of all, the reason such team work is tolerated in schools is not necessarily one of academic preference; rather, it is usually done this way because there are more students than instruments and long work benches. However, where team work is not the rule, try talking the instructor into instituting it, at least in your case. If he refuses, bring a reader into his ever-so-important lab and do it that way.
My classroom work was done using very standard methods: Textbooks were either transcribed into braille or onto tape by volunteer organizations (of which there are many), or supplemental reading was done by paying fellow students as readers. I would investigate which books were going to be used (doing this at the end of the previous year), whereupon I could make a decision as to which I should turn over to transcribers. Very often, only three or four chapters would be used out of a book; why make the poor volunteers do the whole thing?
In the lectures, I took braille notes with a "slate and stylus," or in some cases, used a tape recorder where professors went too fast for note-taking.
I took examinations in several ways: Teachers would often dictate the test to me immediately preceding the period, after which I would take the test in braille; I would then read the work back to them at the end of the period. Very often, I would bring a reader to the teacher's office; he would read me the questions and then write down the mathematical procedures according to my instructions. (I would tell my reader what to work out on his slide rule, and I would keep track of the decimal places.) Some teachers preferred to take the role of my reader and give me the test directly. I put forward these options and negotiated with the instructors as to which would best suit the situation.
Preparing homework assignments was always an issue for me. I can tell you to type them out, but you may not live long enough to carry out this monumental feat. I worked out a very clever approach with a few of my instructors: After the previous day's work was discussed in class, I would assess my performance and just tell my instructor how I did. This requires a feeling of trust on his part, but he is just as anxious to get out of having a problem with you as you are to solve it with him--it sometimes worked. Other professors just figured that if I was doing o.k. on the tests, the error in grading they would get by not counting the homework would be insignificant.
You will find it well worthwhile to be honest, by the way. It gives you license to take tests home, to get occasional ones transcribed ahead of time, to do portions of labs at home, to take major tests at different times (making your reader-scheduling problem minimal), etc. Some professors won't hear of it--the world cheated them, and you're just waiting for your chance to do the same. However, you can always argue that, to arm yourself for future job hunting, you need to be honest with yourself--your credentials must be valid for you as well as him. (Sometimes, they'll even buy that.)
Above all, hang out in the coffee rooms, radio clubs, student divisions of professional organizations, mathematics "help lab" (there always is one, probably in the library), etc. The purpose of this activity is to get a generous supply of pals. Those places are social instruments for them, but they are vital resource's for the blind student. The more pals, the better; you can easily wear one out by asking too much of him, but spread your supplemental help out over ten such friends and they won't remember you utilized them.
Diagrams and Charts
For all the "flap" that's made of these things, one would think science came from
drawings in the pyramids. You must never forget what they truly are--only methods of communication that sighted people have designed before you got there. Likewise, you must never forget what you need from them--an understanding of the principles they convey (not necessarily their shapes nor their
I have often been asked, "When are you going to start putting raised-line drawings in your magazine?" The answer is never!
I say "never" for three reasons:
Ms. Jane Corcoran of San Mateo, California, once said in a transcribers' seminar, "What's eye appealing is often fingertip appalling." The amount of detail that publishers crowd into diagrams is amazing--when you extract it all and take notes on it--and they are
perennially trying to save paper by overdoing it. Therefore, in order to make useful diagrams for us, they would have to be interpreted and then redrawn. That process is inefficient.
The arguments in favor of diagrams are often weak ones; even those who use them
don't always know what they get out of them. For example, it is often stated that a sighted person, in looking at a schematic diagram, sees the whole thing at once and can make judgments about the circuit at a glance. Nothing could be further from the truth, at least when considering complicated circuits without familiar arrangements. Every sighted person I ever knew, when picking up a diagram, goes "Hummmmmmmmmmm." It's only after breaking the thing down into small blocks that he has any idea what's even in the
thing. If you don't believe me, explain to me why "block diagrams" and "flow charts"-both generalized statements--are so prevalent and popular.
Well then, as long as we are all trying to integrate small concepts together into larger ones, and since diagrams would have to be interpreted for us anyhow, why not put ours in an organized verbal form? They will be like good college notes. In fact, the
density of such good notes" and their proven track record in usefulness to the blind scientist are the best reasons for sticking to them. This is the third reason for rejecting a medium which is ill-suited to our abilities as blind people.
The point of all this is to approach every graphical problem with the idea of getting the concepts of why it should look the way it does, or what feature your sighted counterpart is going to carry with him to the test. Whether they graph the decay of radioactive material or the cooling of a tea kettle in physics class, it is most important for you to note that the descending curve changes in constant percentages over time. In one "time constant" (maybe seconds or maybe years), both examples will be "cooler" by 63%. After another "time constant," their contained energy will have decreased by another 63% (it will lose 63% of its "previous balance"). Have one of your "pals" draw this curve;
then, every time it comes up in class (which may be every few seconds), you will know what they're talking about, and braille transcribers can get on with other people's work.
This isn't the full story, in all truthfulness. In studying antennas and transmission lines, we had abominable things called "Smith Charts" by which calculations could be done graphically. While it was impossible for this blind person to have one, I became adequately adept at telling a reader how to mark them up on tests. I was content to know how they were conceived, and basically how they are used.
There is more to be said about training readers to read technical material--how to get them used to describing schematic diagrams, etc. An excellent book on the subject was written by Dr. Lawrence Chang.* This book primarily outlines how to read mathematics out loud, but it does a superb job on the subject of diagrams and charts as well.
A hint as to how easy this is to learn can be gotten from listening to ham radio--a heavy technical discussion--and watching them describe things to each other without their precious visual aids.
Confessions of a College Student
You didn't really believe all that stuff up above there did you? [Anybody whose magazine is as consistently late as mine is has to be a trifle suspect.] To be honest, sometimes I wouldn't bother to work something out on the homework, for example. Why bother, "wasn't going to do it anyway." Nevertheless, some workable principles are set down here (all
of which I've tried out, anyhow).
*Handbook for Spoken Mathematics (Larry's Speakeasy), available from the Technical Information Department, Lawrence Livermore Laboratory, University of California, Livermore, CA 94550.
As my father used to say, "Don't do as I do, do as I tell ya."
I have been unable to write one--a conclusion. I would, however, like to slightly change the subject and quote a favorite
author of mine (me, of course). The following is a concluding statement I wrote to a university admissions board which refused to accept a student on account of his blindness. It accompanied a skeletal version of this paper, and it ended like this:
Blindness is a darned nuisance; it forces us to do things in different ways, and we are never "completely independent" in the strict sense of the word. Yet the inability to "see" is often outweighed by the "trials by fire" to which we are sometimes put to gain acceptance in pursuing our natural inclinations. Yet still, trials by fire are dwarfed by absolute barriers:
"Sorry, this avenue has been closed by decree!"
We live in a competitive society-but it is also a society of fairness. A burden of proof rests on every student; can he "cut the mustard" or not? Our sense of fairness causes us to rail against any attempt to stand in the way of an able-bodied student pursuing his interests. Why is it not so for his blind counterpart?
The barriers before us are not built on unfairness. Rather, they are born of burdens which people wrongly assume. "In all fairness, Mr. Doakes, I feel I would be remiss in not dissuading you from this fruitless course you're on." Only the results are unfair. The "burden of proof" (and the freedom of choice) has been unfairly lifted from the shoulders of its rightful owner, and the heavy burden of directing someone's life course rests on the beset advisor.
I urge you to let this blind student test his mettle in the school of engineering. No matter how it turns out, his future career decisions
will be based on a legitimate investigation of his strengths and weaknesses. In the meantime, you and I have burdens of our own; let us not don someone else's unnecessarily.
Would you like to know how they replied?
"We have decided that it would be unfair to admit the student, since we have no special facilities for him." Well, as Sinbad the Sailor once said, "Give not advice to a fool, for he cannot understand it."
The editor must confess that this is one of his favorite "editorial features." Without fulfilling past promises, I can go ahead and dream up new futuristic fantasies with the unabashed arrogance of bragadociosity and the pretense of entrepreneurship. On the other hand, I have to gloat over my successes of the past, some of which, include promises that have been fulfilled.
* * *
First of all, I am proud of the fact that most major test instruments (including the oscilloscope) have been described in adapted form within these pages. A blind person could now stand up to an employer and say, "Oh yes, I have the information on how that measurement could be done." (Remember, you can always write to Smith-Kettlewell for help, if it turns out that you need some variation on the projects which have been presented; very often, we can tell you where to buy something or how to build something that will serve your need.)
* * *
As of now, two of the "live tape recordings" that I promised you exist: The first is of three people building identical continuity testers. The second is a three-cassette record of me building a portable VU meter (intended for use with "Walkman-type" equipment). To get them, send us the tapes (clearly marked with your address, and clearly marked as to what these tapes are
for, please). The continuity tester requires one 90-minute cassette, while the VU meter requires three 90-minute cassettes. These are recorded at standard speed, so you do not need a talking-book machine to play them.
The only thing I demand in return is your feedback. Are these tapes useful, entertaining, or a waste of your time?
* * *
Within this issue, another of my "projects" has been launched. This is the one regarding technical schooling and how to get things made accessible. The first step has been taken in the article, "How to Make Technical School Accessible to the Blind." The second step has already been done for us by Dr.
Lawrence Chang in his book "Larry's Speak-Easy," (see previous article). The obvious next step will be to write a paper on how circuit diagrams should be described. Other intermediate steps are unclear to me now, but the final one will probably consist of a "live tape recording" of me working with a reader.
* * *
The "kit project" was both a success and a failure. Everybody we tried it out on loved the raised models of the board under construction; every kit that was completed was done properly. The trouble is that only five of the units were ever attempted; sufficient interest was not shown by most of the test subjects to buckle down and build the thing. What this means is that, although the technique of making thermoform models is sound, the marketability of such items is at least in serious doubt.
Perhaps what we need is new direction. I will make the following offer to you entrepreneurs out there: If one of you feels he or she can market a kit of a special device (not your favorite commercial kit--Heathkit or the like), I will design the braille (meaning raised) documentation for it. You
pick the device, work out the availability of parts, and set up the system by which you can sell them. I'll make copyable relief masters for you with which a blind person could independently make the animal.
* * *
As a new project, we have every intention of making the "Little School" (our electronics training program) exportable. In other words, I have the go-ahead to make kit-like models of instruments that are popular in our program. (As with all of our Smith-Kettlewell devices, we must then find someone who is willing to make and market the thing.) Test instruments have been chosen because, when the student has built one, it empowers him to independently do something in electronics.
The format of the program will be that of "The Smith-Kettlewell Continuous Kit." Each project segment will consist of building a test instrument--then finding something to do with it as an exercise. Each segment will depend on the instruments before it to make it accessible. The following is the course outline as I perceive it:
- The first instrument is a one-transistor continuity tester. Test exercises will include: checking audio patch cords, checking the polarity of a diode, checking a transistor, and making a light probe.
- The second project will be an audio amplifier (using an LM386). The continuity tester will be used to identify the polarity of the electrolyte capacitors, for testing the volume control, for identifying the terminals on the input jack, and for checking the wiring. Test exercises will include checking microphones and other signal sources (monitoring the output of a tape deck, for example), and amplifying the output of a diode detector (making an amplified crystal set).
- The third project will be a test oscillator. This will require identifying a couple of resistors with the continuity tester, and testing its output with the amplifier. Test exercises will consist of checking earphones and loudspeakers, checking tape machines for wow and flutter, and perhaps some elemental signal injection (listening for the oscillator with other amplifiers and AM radio receivers).
- The next step will be to build a resistance bridge, using the above oscillator to drive it, and the amplifier to detect its output. The continuity tester will again be needed to identify the resistors (standards) contained in the bridge, and to ferret out the switches. Exercises will include measuring a couple of resistors, and checking the conductivity of a few liquids.
- Next, a capacitance bridge of similar design will be driven and detected using the oscillator and amplifier. I'll have to consult with a physicist (probably Dr. Benham of Science for the Blind) as to what the test exercises should be.
- Next will be a meter reader of some sort, there being several simple ones to choose from. The bridges will figure heavily in identifying the various parts. Testing batteries and the polarity of voltages will be the test exercises, along with checking circuit voltages in the previous projects.
The "course" could be dropped at any time; no matter how few instruments the student chose to build, there would be a use for those he has done. If he were to keep going, he would have a battery of test instruments that would make him employable.
Plans are afoot to accomplish much of this within the coming year, and considerable interest in handling the eventual project has been shown by Hadley Correspondence School and other agencies. Our first "test" of the system is in January, 1985; I am giving a class in building a code-practice oscillator at a "camp" being sponsored by Courage Handi Hams. If this goes well, I'll blaze away on the "relief models" and other documentation for "The Smith-Kettlewell Continuous Kit."
* * *
Some computer stuff is coming up. We are now evaluating some prototypes: one is an audible "breakout box" (a test instrument
for ferreting out RS232 ports), and a "transmission-in-progress alarm" for MODEM users (it'll tell you when down-loading has been completed). Any theory articles on computers will be highly technical; there are a fistful of "basic introductions" to computers which I will try to list.
* * *
The computer in relation to the magazine is making headway. I do all my writing (and editing of your articles) on a word processor now. When I'm done, I hand a diskette to Ann Lewis (the real and true editor of this thing), whereupon she translates these writings into English, prints it out and
sends it to Clovernook. The eventual plan is to have the braille printer grind it out directly from the diskette.
Just for your curiosity, I am using an Osborne computer which is "hardware modified" in Germany by a company called Frank Audiodata. Within its keyboard is a whole additional computer (along with 64 kilobytes of random-access memory); along the edges of this keyboard are things called "TASO sliders." I direct the "talk chip" to any part of the screen I want by positioning the sliders. Videogame-like tones tell me about upper case, lower case, punctuation, and other symbols. When I have found my place with the tones (which is childishly easy), I press down on one of these sliders and it spells or reads to me. It's nothing short of Mr. Kaatz's pajamas, and I'll write it up
* * *
"My! How that windy editor goes on and on," you say. My reply is, "Now aren't you glad the magazine is perennially late? This gives me extra time to think this stuff up.
Please don't forget to re-subscribe (at current prices) and together we'll Sally Forth (whoever she is) into the next year. May you all be treated with fairness and with good prosperity. You are 300 of the most technically accomplished blind people ever to walk this earth, and it is my pleasure to know you. Thanks from your editor.