This overview of blind soldering techniques was adapted from an article by Bill Gerrey as background
reading for a Blind Soldering Workshop collaboratively offered by Smith-Kettlewell and the LightHouse for the Blind
and Visually Impaired of San Francisco, November 4-6, 2016.

SOLDERING BASICS

By Bill Gerrey

Introduction

This overview of blind soldering techniques was adapted by Josh Miele for use from Soldering, Part II, By Bill Gerrey, originally published
in the Smith-Kettlewell Technical File, Volume 2, No. 4, Winter, 1981. The original article included extensive product references, suppliers of equipment, and pricing, many of which were out of date and have been omitted in this adaptation. The present version of this article was developed as background reading for a Blind Soldering Workshop offered by the LightHouse for the Blind and Visually Impaired of San Francisco, and the Smith-Kettlewell Rehabilitation Engineering Research Center, November 4-6, 2016.

Forming a Solder Bond

 

The principles of forming a solder bond can be summarized as follows:

1. Molten solder acts as a solvent–it dissolves metal from the surface of the pieces being joined, forming a bridge of alloys from one metal to the other.
2. All the metals being joined must reach the “alloying temperature” in order to be soluble in molten solder. The metals must be in firm contact with each other so that they all reach this alloying temperature.

2. 1. Heat transfer from the hot iron to the joint of the metals must be extremely efficient to afford good soldering and to prevent damage to connected components of the work. If the transfer of heat is done inefficiently, a long time will elapse before the adjoining metals reach the alloying temperature; during this time, considerable energy will be absorbed by the components and damage may result.
   2. In order for heat to be efficiently transferred to the metals from a hot iron, a complete metallic path must be established between the iron and the work. In fact, the iron itself must be involved in the continuity of alloys. The iron and the metals being joined must all have their surfaces in solution with the molten solder; this is known as “wetting”.
3. Oxides on the metallic surfaces prevent wetting by the molten solder; the solder cannot reach clean surface metal to alloy with it. Furthermore, oxides build up very rapidly at high temperatures, insulating the hot iron from the work. A chemical “reducing agent” known as flux, must be applied to all the surfaces during soldering to strip these surfaces bare of oxides, allowing the formation of pure metallic alloys.
4. Rosin Flux (used in electrical soldering) is a fairly active reducing agent when heated, but remains inert at temperatures below soldering temperatures. Its resistance to chemical interaction after the solder has cooled makes it ideal for electrical work; its residue is non-corrosive.
5. Given ideal conditions, soldering is done in the following manner: The tip of the hot iron is put in contact with all the adjoining metals. Flux-core solder is put in contact with the work and the tip of the iron which causes a column of molten solder to flow between the iron and the work. After this initial melting of solder, the application of additional solder should primarily be fed to the work pieces and not to the tip of the iron. Solder which is applied to the iron alone and which subsequently runs down into the work will generally not involve itself in bonding. Its flux will be used up cleaning the iron and not the work; it will not be able to get through the oxides onto the bare metal surfaces. Feeding solder to the work alone maximizes the effectiveness of the flux, and provides a good indication as to whether or not the metals being joined have reached soldering temperature.

Continuous – Heat Soldering Irons

Much of what follows is a clean break from theory; it is a highly subjective discussion of the techniques I use when soldering with a continuously hot iron. Many of the statements to follow are refutable. Take each stated technique as a seed from which you can “grow your own”.

There are two basic classes of continuous-heat soldering irons, simple garden variety constant-power irons, and “temperature-controlled” irons.

Constant-power units are comparatively inexpensive. Their heating element is a simple power resistor which is energized continuously. Their main disadvantage is that while they are not in contact with a work piece, they must dissipate all their heat energy in free air, which means that they reach fairly high temperatures between soldering operations. Their tip temperature may approach 1,000 dg F, (about 450 dg C) while the iron is in the rest stand. To protect the “tinned” surface of the tip from oxidizing, at these high temperatures, it is crucial that fresh solder be always present on the tip.

Temperature-controlled irons are those which have “thermostatically-controlled” mechanisms for sensing and maintaining the temperature of the tip. With these units, the temperature is held to a specific value, whether the iron is in use or at rest. Typically, these irons are designed to maintain a tip temperature of 650 dg F (about 350 dg C).

The tip of a temperature-controlled iron is not subjected to heat cycling over a wide range of temperatures, and the overall tip temperature is lower (more than 300 dg lower). These features give rise to a longer tip life. In addition, the likelihood of a solder joint reaching a very high temperature, which can damage the flux, is minimized. Finally, the 30 percent reduction in tip temperature may be slightly less injurious to the fingers, if the job is such that the tip must be frequently touched. (In all fairness, it should be stated here that Dennis Bernier, Vice-President of Research and Development at Kester Solder Company, prefers a well-designed constant-power iron over temperature-controlled ones. He argues that a well-designed constant-power iron is able to maintain a fairly constant temperature, and that temperature-controlled irons can often subject the work to electrical transience as they switch on and off. He also recommends that when choosing a temperature-controlled iron, obtaining one with a tip temperature no lower than 700 dg F is preferable for efficient heating of the work.)

When choosing a soldering iron, pick one with a high power rating, so that it can supply heat energy to the localized area of interest at a much faster rate than energy can be conducted away from the connection by components of the work. Small-sized, lower-power irons are made for specialized applications, such as miniaturized assemblies on which larger irons cannot be maneuvered into position. (1 used a 25 watt iron for years, only to find out that components were absorbing enough heat energy to be damaging, while I shifted from one foot to the other waiting for the solder to melt). The iron should be as large as can practically be used, given its physical size and configuration.

Unless they are a very small size, temperature-controlled irons are designed to supply high levels of heat energy when they are called upon to do so. When the tip temperature drops below their specified value, a high amount of energy will be supplied by the iron until the tip temperature is restored to the rated value.

Constant-power irons, on the other hand, only have their given power rating available for transferring heat energy to the work. Ideally, given the size of electronic components used in most assemblies, an iron of 50 watts or more enables the user to make connections quickly and efficiently. However, for the blind technician, irons of this power rating may have unfavorable physical characteristics; they are often very long, and their heating element may be comparatively large in diameter. The blind technician may wish to compromise on the power rating to obtain an iron of smaller physical size. I recommend not using irons of less than about 35 watts.

Key Physical Parameters

By picking an iron with certain key physical characteristics, you can optimize your accuracy and stability in performing the task of soldering.

The length of the hot portion of the iron (from the handle to the tip) should be as short as possible, so that your sense of the tip position can be accurately predicted. The iron becomes an extension of your hand; the position of your hand and the angle at which you hold the iron are valuable pieces of information which you must use to predict the tip’s location. The shorter the iron is, the more meaningful will be this information.

By the same logic, the handle of the iron should be well enough insulated from the heat to afford holding the handle at its extreme forward end.

The diameter of the “barrel”, which is the heating element, should be as small as possible to minimize the likelihood of its contacting nearby wiring or your other hand.

It is my experience that a great advantage in stability can be gained from choosing a tip which has flat contact faces. In contrast to this, the tip style which has gained overwhelming popular acceptance is conical in shape; it has no flat contact face. When holding a conical tip against the work, the contact force must be exactly perpendicular to the surface of the cone, otherwise the iron will tend to slip or “glance” off the connection. In other words, holding a round tapered tip against a work piece is difficult, and is subject to instability. I have found that by using a tip with flat contact surfaces, “glancing” of the iron off the work is less of a problem.

Replacement tips which have flat contact faces are available for almost any make of iron. In general, three such tip styles are available from soldering iron manufacturers – pyramid-shaped, chisel-shaped and screwdriver-shaped tips. (Incidentally, all these styles have far better heat conductivity than does a tip of conical shape). Screwdriver tips are the most suitable for electronic assembly, since they are usually thin enough to fit between closely spaced terminals. Whichever style is chosen, the handle of the iron should be marked adjacent to each flat surface, so that the tip can be properly oriented with respect to the work. The handle can be marked by filing notches into it, or by attaching narrow strips of Dymo tape along it.

Care and Feeding of the Soldering Iron

A soldering iron is a very vulnerable instrument. Operating at extremely high temperatures, the iron can supply enough heat energy to promote a variety of “endothermic” chemical reactions, all of which are detrimental to its effectiveness.

Since the surface metal of a soldering iron tip is chemically active, it is prone to oxidation; and this tendency is greatly accelerated at high temperatures.

During idle periods, the heat of the iron can carbonize any flux residue present on the tip.

The iron may accidentally come in contact with foreign materials which melt when subjected to its intense heat. Some notable examples are plastic building materials, insulation on the wiring, painted surfaces, and insufficiently damp cleaning sponges. If deposits of such foreign matter melt off on to the tip of the iron, they quickly carbonize and cling stubbornly to the tip.

Any soil on the tip acts as a heat insulator, and it renders the iron incapable of effectively heating the work. The only protection the iron can have against this soil is to be kept wet with solder. Since the surface metal of the tip will not be exposed to the atmosphere under these conditions, oxidation of the tip metal itself will not occur. Any carbonized residues will tend to “float” on top of the molten solder, thus protecting the tip itself from contamination.

Therefore, a solution of molten solder must always be kept present on the tip of a well cared for iron. The solder-wet tip can easily be wiped clean on a damp cleaning sponge, but this procedure should be followed soon after with the application of fresh solder to the tip.

In the normal sequence of making solder connections one after another, the tip of the iron is kept reasonably wet automatically. However, an occasional “slap-dash” application of solder to the tip assures that voids in the surface solution do not go untreated; a good bath in fresh flux will strip oxides and other contamination off the surface metal. Initially, of course, new tips should be bathed in fresh solder before being used.

Special mention should be made here regarding the simplest of tips, those which are made of bare copper. Copper is extremely soluble in solder. Copper from these tips is actually dissolved into each solder connection; these tips eventually become pitted and worn away. They can be redressed by filing or sanding them down to a smooth new surface, at which point they must be treated as a new tip. Never attempt this redressing procedure on steel or iron-clad tips (see “Soldering”, Part I).

“Tinning” the iron specifically refers to applying a coat of fresh solder to the tip. This can be done in two ways. If the iron is cold, wrap about three inches of solder around the tip and turn the iron on. (To some people, these three inches may seem like an excessive amount of solder, but the point is to assure that the entire surface of the tip is bathed in fresh solder. Overdoing the amount harms nothing.) If the iron is to be “tinned” while hot, solder must be “brushed” along the tip. To make sure that the entire tip is being bathed in fresh solder, turn the iron slowly while “brushing” the solder over the tip.

Finding the tip of a hot iron with a piece of solder is no easy task.

To aid in doing so, rest both hands against some familiar object, such as your vise or the rest stand, so that you have some idea as to where the iron and the piece of solder will intersect. I often extend the piece of solder an inch or so beyond my projected point of intersection, thus allowing the iron to “cut” the solder to the exact length.

Do the “tinning” procedure over an unimportant surface which is not flammable. It is a good idea to “tin” the iron over a wet cleaning sponge, but remember to retrieve the solder droplets from the sponge; they will be larger than those left in the sponge after normal wiping, and you do not want the iron to pick them up later.

The iron can be cleaned by wiping it on a wet cloth or a wet cellulose sponge. Whichever you use, the item must contain nothing which will contaminate the iron. For example, no cloth having components of polyester are acceptable. Also, many general purpose cleaning sponges contain chemicals which can soil the tip. Above all, the item used must be wet (dripping wet is acceptable). This is essential, since while the iron is being wiped free of its protective excess solder, it is very vulnerable to charring foreign matter.

Sponges designed for this purpose are available from various soldering equipment manufacturers. The best cleaning sponges are those which envelope or surround the tip when it is being wiped. These sponges can either be convoluted (being made up of lobes), or they can be comprised of a “sandwich” of separate sponges standing on edge. With simple flat sponges, several passes must be made (rotating the iron between each pass) to assure that the tip has been wiped on all sides. This tends to cool the iron more than is done by making a single pass through a sponge of complex configuration. (For the blind technician, it is vital that all droplets of excess solder be removed, since they can cause serious burns. Dennis Bernier of Kester Solder Company pointed out to me that wiping the tip on a simple flat sponge tends to transfer droplets to the unwiped side of the tip, and does not assure that they will be removed.) Wipe the iron immediately before soldering. After soldering has been accomplished, return the iron to its rest stand; do not wipe the tip free of excess solder at this time.

Many accidents can happen to damage the iron. All of these accidents are preventable if reasonable steps are taken.

The power cord of the iron should be kept off to one side at all times to prevent the iron from coming in contact with it. In fact, all cables should be kept well out of the way, even if they do not pose an immediate electrical hazard. If the tip of the iron comes in contact with any such cable, it will become contaminated with very stubborn soil.

Plastic handle tools should be kept clear of the rest stand to avoid being grazed by the tip, resulting in its contamination.

Finally, the tip should not be banged into things which can mar its surface. To avoid striking the tip on sharp corners and edges of the rest stand, carefully note the position of the rest stand so that you can approach it slowly and gracefully with the iron.

Handling the Iron

This section covers a lot of territory – practice reaching, establishing well-defined reference points and rest positions (“land-marking”), and touching and holding the iron. The limitation of writing is that these ideas cannot all be conveyed simultaneously. As with swimming, which can be described as the integration of kicking, paddling, breathing, and adopting a good posture, the components of this discussion must be taken together when performing the task of soldering.

It goes without saying that the techniques to follow should be practiced while the iron is cold. In addition, a practice iron which is always cold may be worth having. A dummy iron can be made by thrusting a pencil through a couple of bottle corks of appropriate size; the pencil should protrude the same distance as does the hot portion of your iron, and the corks should be of a size that roughly simulates the handle of your iron. With this tool, you can take a practice run any time you want to. Even for veterans like myself, an occasional need arises for a practice shot. For example, when working in a nest of wiring or when working in a small space, a practice run can lead the way to taking the best approach, and may spare you an unpleasant surprise.

Holding Instruments

Surgeons, jewelers, and people working in micro-assembly all know how to hold their tools and to support their hands to maximize control and stability. We will take the following lessons from them. (My thanks to Dr. Irene Gilbert of University of California Medical Center and to Dr. Brian Brown of Smith-Kettlewell Institute for these lessons in physiology.)

We possess one set of muscles capable of precise manipulation, the thumb and fingers. The muscles have a large number of nerve fibres dedicated to them, and a large part of the brain is devoted to controlling them. In Dr. Gilbert’s words, “The area of cortical neurons overseeing the thumb alone is almost as large as the area over-seeing the entire leg and foot. Therefore, precise manipulation of instruments can best be done with the thumb and fingers.

Coarse muscle systems which are not designed for fine work, namely muscles controlling motion of the arm, should be taken out of play. Free motion of the arm has a profoundly detrimental effect on the precision of finger motion. The main muscles which operate the fingers are not actually in the fingers, they are in the forearm. The fingers are controlled through a complicated pulley system of tendons and ligaments in the wrist. Precise control of the thumb and fingers cannot be attained through an unstable pulley system.

Much of what is seen as hand and finger tremor is caused by failure to stabilize the arm and wrist. People who do fine work learn quickly to stabilize their wrists and forearms on solid objects. Dr. Gilbert remarked, “I once made a plaster half shell of my forearm from elbow to wrist and mounted it through a ball and socket onto a base. The shell could pivot and rock, and yet hold my wrist and forearm steady, leaving my fine hand and finger muscles to manipulate freely and precisely.” At the very least, your elbow should be braced against your body, and your wrist or hand should be resting comfortably against some solid object. Bracing your hand against the work piece is often sufficient; however, books, blocks, or the spool of solder should be used as needed.

Holding the iron like a pencil is usually advocated in discussions on soldering. With the side of your hand resting on the stabilizing object, the iron is held between your thumb and first finger, with the middle finger curled under the handle to provide a supporting cross-bar. I modify this grip by uncurling the middle finger and placing it along the handle under the index finger; this arrangement gives me better vertical position information. I hold the solder between my thumb and middle finger of the other hand, leaving the first finger free to touch and guide the iron where necessary. To maximize control of it, the solder should be held about three-quarters of an inch from the end.

Land-Marking

In the performance of all tasks involving movement, the sense of joint and muscle position (kinesthetic sense) is relied upon heavily. When pianists and typists have reached perfection, they no longer look at the keys. A skill is really learned when one can say, “I can do it with my eyes closed.”

In soldering without visual feedback, much about the position of the iron can be predicted using the kinesthetic sense, but the limits of this bio-physical system must be understood. “Can the sense of the position of your hand ever achieve a resolution of one-tenth of an inch, which is necessary for soldering integrated circuits?” This question must be answered with another question, “Where is your starting point with respect to the target?” The accuracy with which a movement can reliably be made is a fixed proportion of the distance to be moved. Generally, it is about 5 percent of the distance to be moved, and so to achieve the accuracy necessary for soldering integrated circuit pins, the last movement should be from a land-mark about two inches away. I propose that a few reference points and rest positions along the way to the target be identified, a procedure I shall call “land-marking”.

Note the position of main items associated with the project on which you are working. While holding the iron in your hand, these items can be located with the heel of your hand or with a couple of straying fingers. By bringing the iron over to one of these cross reference points, the distance to the target can be reduced to at least one-fifth the original distance (from the rest stand). By staying in contact with these items (using them as rest points to stabilize your hand), the iron can be very precisely controlled with the thumb and fingers.

For the next stage, the iron can be used to do some of the land-marking.
There are usually a number of relatively inert items which will not be harmed by bringing the barrel or the tip of the iron into brief contact with them. The edge of the chassis, the handle of your vise, or strategically placed C clamp, alligator clip, or clip-on heat sink are examples worth noting. If you are as lazy as your Editor, you may use the edge of the circuit board, a nearby terminal strip, or the body of a Bakelite component for land-marking with the iron (naughty-naughty). Make sure that the tip of the iron is wiped free of solder before you do this, or you will spill droplets of solder into the project. Remember, be gentle with the tip at this time, since it will be vulnerable to damage without its protective coating of excess solder.

The final land-mark should be chosen so that you have a short hop to the target. Regarding the choice of this landmark’s position, Dr. Gilbert suggests that the following information on current research be noted:

1. Movements made horizontally are more precise than those made vertically.
2. One is more accurate in knowing a movement’s direction than the length of the movement.

During the final reach, the iron becomes your “cane”. In this way, it can indicate to you when it has come to rest on the target. Unlike the “cane” traveler, the person wielding the soldering iron has control over the features of his terrain. He can arrange for the target to have unique features. Some examples of this are listed below:

• If a component is being soldered into a printed circuit board (PC board), leave the leads long, so that the target is “the only tree in the forest”. These long leads will be easy to find with the tip of the iron, especially if you remember to cut the excess wire off components you have previously soldered.
• A wire being soldered to a terminal lug may be arranged so that its end protrudes beyond the terminal, making this terminal easy to find with the iron. After it has been soldered, cut off the excess wire.
• When wiring integrated circuits on perforated board (point-to-point wiring), lay a component lead across its intended IC pin; cut it off so that it extends conspicuously beyond the center line of the IC (between the two rows of pins). When approaching this connection with the soldering iron, reach not for the IC pin but for the point at which the component lead crosses the center line of the IC. In other words, fish for the extended wire with the tip of the iron; when you have found it, follow it over to the pin. After this connection has been soldered, cut the excess wire off close to the pin and proceed to the next pin. Arrange the order of your tasks so that the pins are soldered in consecutive sequence (it is harder to hit the pin if it is between two previously soldered ones). (You will have more space between pins and have less trouble with bridging them if you use only one component lead per pin. Other components going to this pin can be soldered to the lead of the first component.)
• When soldering multi-pin components on which the pins are very long, such as PC-mount potentiometers, and wire-wrap sockets, solder these pins in sequence, and cut them off near the solder joint as you go.

Touching the Iron

With some jobs, such as soldering components with short leads into a PC board or removing defective components from a PC board, no convenient system exists to give the target unique features by which it can be easily found. In such cases, the iron can be guided into position by a free finger of your other hand. Believe it or not, the hot iron can be touched.

In touching the iron, two overriding principles must be adhered to: the tip must be wiped clean, and you must not make any quick, uncontrolled movements.

Any fisherman knows not to make fast jerky movements around his tackle, otherwise he may impale himself on a hook. The same philosophy should prevail when handling a hot soldering iron. The more relaxed and even your motions are, the less chance you have of coming into unexpected firm contact with the barrel or tip of the iron. If the job is such that you must touch the iron, do so with smooth, light, brushing motions. (Your Editor considers that fear of such things is relative. I would much rather solder than light a cigarette, which scares the Devil out of me.)

Tactile Feedback

When you have hit the target, several indications can be used to affirm that it is the desired one. At this point you have a “cane” in each hand the iron is in one hand, and the solder (which awaits your arrival at the target) serves as a “cane” in the other hand.

Using the iron as your “cane”, the contour of the target should make sense as you gently scan it with the iron.

The solder, which is being held against the connection by your other hand, will vibrate when the iron touches the connection. At this point, move the solder over to where you suspect the tip of the iron is resting on the connection. If it melts, the iron is on target and you were right about its position. Bring the solder back to a point which is not in direct contact with the tip of the iron and feed the desired amount of solder to the joint (from one-eighth to one-half inch depending on the size of the connection and of the solder).

The solder may melt immediately when the iron touches the connection; this is your indication that the iron and the solder touched the target in the same place. Often, you will lose the connection with the solder. When this happens, feel around with the solder until you apply it to the connection which causes it to melt.

Another indication of hitting the desired target is that the wiring and components associated with the connection will heat up. A spare finger of the solder-feeding hand can be used to monitor this condition.

Indications that you have missed the target are:

• Components associated with a different connection may heat up, indicating that you have found their connection instead of the desired one.
• The solder will refuse to melt when it is scanned over the connection. Scanning adjacent connections with the solder will reveal which one is being mistakenly heated.
• If you suspect that you have gotten on to the wrong connection, there is a clue which may indicate to you whether or not this connection has been previously soldered. If small motions of the iron feel “squeaky”, the surfaces against which the iron is in contact are wet with solder, which probably signifies that the connection has been soldered before (if the work materials have been previously “tinned”, the iron may be squeaking against individual items rather than a fully completed solder connection). If small motions of the iron do not feel “squeaky”, the items you have contacted have never been soldered.

Tools and Accessories

General Comments

When people refer to the “balance” of instruments, they are actually referring to the ease and control with which these instruments can be manipulated. Used in this sense, the term “balance” implies that a favorable compromise in weight and distribution of mass was made in the design. In general, the tools of the highest utility are those which are light in weight, and which present a minimum of inertia.

It follows that smaller tools are easier to control than larger ones, because characteristics unfavorable to manipulation become less significant.

For many years I used a large fancy jack knife whose handle contained a pair of pliers. However, for many small jobs (such as stripping wire) it was clumsy to hold and would frequently topple out of position. Since then, I have come to prefer very small pen knives with no extraneous gadgets in the handle.

The above principles can be expanded to include all hand tools used in soldering. Short light-weight tools which can be held near their center of gravity afford precision control and promote stability when holding them in place.

With regard to vises and holding clamps, “low-profile” systems are preferable. Having the work close to the work bench puts you in a comfortable position and greatly increases the number of objects against which your wrist can be stabilized.

Cleaning Sponges

The cleaning sponges which come with the rest stand of most soldering irons are of the simplest configuration, flat. While these are better than using your apron, several passes must be made over them while the iron is being rotated in your hand. This cools the iron, weakens the power cord, and does not guarantee that the tip will be wiped free of dangerous droplets of solder.

Tweezers and Heat Sinks

Forceps which can lock or clamp on to wire leads are very useful tools. These devices can be clamped on to the leads of heat sensitive components in order to absorb the heat and prevent damage to the components. These forceps can be used as “handles” by which wire leads are held in place while soldering them.

My favorite tools of this kind are surgeons’ forceps. Shaped like scissors, they can be used as very small pliers to aid in forming wires around connection terminals. They have mechanisms allowing them to be locked in to place. Being made of stainless steel, they cannot accidentally be soldered into the project.

Spring-loaded heat sinks can serve many of the same purposes.

Vises and Holding Devices

A good strong vise is the best tool for rigidly supporting a work piece. A vise takes on a new measure of convenience when it can be swiveled to orient the work in a favorable position for soldering.Besides traditional vises, fixtures specifically designed for holding circuit boards have become very popular. Many such holders grip one edge of the board between two strips or blocks. In order for this type to be used, a section along one edge of the board must be left free of circuit elements. Holders made by Panavise on the other hand, hold opposing edges of the board between two spring-loaded V-shaped channels. This arrangement permits the greatest flexibility of board layout.

All board holders have provision to flip the board over, so that work can be done from either side.

 

Conclusion

The basic differences between a sighted person soldering and a blind person soldering can be described in terms of feedback. There is no argument that the blind person is operating “open loop” (without direct feedback) part of the time. In reaching from one place to the next and in ascertaining what is actually happening during the soldering process, the blind person is forced to use discontinuous bits of information, whereas his sighted counterpart has information which is continuous. The gaps – the discontinuities in information can be made less significant. By shortening the reach, a target can be hit fairly accurately without vision. By attending to alternative or indirect cues, deductive reasoning can verify facts which are not seen. These principles are not new, but they have tragically remained unsaid.

Blind people have been soldering throughout this entire century. As for myself, I was employed as a technician for three years building very complex electronic equipment. Since then, I have wired the prototypes of my own engineering.