At the end of the chapter on drawing I explained how you could make models of mechanical movements of cardboard. And you will remember that the purpose of these simple models is to clear up points that are hazy when you are working out your invention on paper.

Kinds of Models.—Now besides cardboard models there are some other kinds, the chief ones being (1) rough models; (2) scale models and (3) working models, and each of these kinds is useful in its own way. The kind you should make, or have made, will depend on the bulge of your pocketbook as well as on the nature of your invention as you will presently see.

There was a time when the United States patent office required a model of every invention for which a patent application was made; as a result the noble patent office finally became a museum filled with antique models instead of an office in which business was transacted for and with inventors.

The government officials then concluded that the patent examiners didn’t really need to see the models anyway and then and there they ordered that a patent application only need be sent to the patent office—with one exception; this exception is made when a would-be inventor applies for a patent on a perpetual motion machine and then he is asked for a working model and if this is not forthcoming—and of course it never is—no further attention is paid to him or to his application.

Rough Models.—After you have made the drawings and experiments which your invention calls for and both have worked out to your satisfaction you will then have a burning desire to see the result of your efforts in a more substantial form.

Some machines in which there are only a few moving parts need not be built up very carefully, or to exact scale or even of the materials the marketable product is to have in it. Very often a model can be made of wood and scrap metals that will do and show everything that you want it to. See Fig. 64.

Should you have to employ a patent attorney who lives at a distance from you, say one who has an office in Chicago, Philadelphia or Boston, a rough model of your invention will be of great help to him for it will give him an insight into its workings and its possibilities that he is not apt to get from studying your drawings and description unless you are a good mechanical draftsman and he is above the average in his profession.

Scale Models.—Scale models are usually miniatures of the full sized machine, that is every part of the scale model is reduced in proportion from the dimensions of the big machine, say 1 inch to the foot or whatever you want to make it.

Like rough models scale models need not be actual working models, indeed in many cases it is very hard if not impossible to make a scale model which will run or work like a full sized machine, unless the model is made very large, as for instance model aeroplanes fitted with motors of any other kind than those made of rubber strands. Fig. 65 shows a scale model of an aeroplane.

Then again sometimes a scale model will work to perfection and when a full sized machine is built it will not work at all as in the case of the heliocopter, that is, a flying machine having a screw with blades like a propeller and which when it is rapidly spun by means of a string like a top will rise in the air to a height and sail away to a distance of a hundred feet or more. Fig. 66 shows a toy heliocopter, or aerial top as it is called. Many attempts have been made to build full sized flying machines on the principle of the toy heliocopter but so far none of them have been able to get off of the ground.

Then again there are many machines that can be made of any size and which will work equally well. Fig. 67 is a scale model of a British express locomotive. It is 4 feet long and an exact scale model which can be fired up with coal and it will make a speed of 10 miles an hour.

A scale model of your invention, if it is a machine, or an electrical apparatus, when built by an expert model maker, makes a mighty pretty display and will never fail to attract attention wherever it may be shown.

Working Models.—A working model may be a scale model as you have seen or it may be a full sized machine or of any size between these limits.

When you have your invention past the drawing board and up to the shop bench by all means make a working model of it and if possible make it full size. This kind of a model is the proof you want that your invention will work when it is put to the test and by making a working model you will find lots of changes little and big that are needed and which when made will improve its operation wonderfully.

And however carefully you have worked out your invention on paper you will find that when you come to make a model, or have one made, you will have to change it not once but many times, that is if it is a machine in which a number of parts are made use of and you may have to re-design it and re-construct it several times.

For this reason it is a waste of money to build a fine appearing and costly model in the beginning but what you should do is to make one that will work without regard to its looks so that you can experiment with it, overhaul it, tear it down, build it up again and so on until you are satisfied with it and the results it produces, if such a thing is possible, before you even begin to talk to a patent attorney about applying for a patent on it.

Nearly every tyro inventor seems to believe that the only way to keep honest folks from stealing his invention is to apply for a patent on it immediately. You will remember I pointed out in the first chapter how to protect your first idea by signatures and affidavits and protection of this kind is just as good, and in my opinion just as safe, and in every way better than to rush off and apply for a patent and—though of course money is of no object—it is cheaper by at least $35.00.

Again as I stated in the preceding chapter if you apply for a patent before you have made a working model of it you will find when you finally get your model finished it will be so at variance with what you have written in your specification and claims that you will hardly be able to recognize it as being the same invention; and besides there will be the trouble and the expense of changing your drawings and specification and claims.

On the other hand when you have finished your model to the point where it will do the work you want it to do you are in a position then to make a new and accurate set of drawings, to write a clear description of how the machine works and to draw up your claims with the certainty of knowing just what you have and what you want to ask for—in a word you are ready to do business with the patent office.

Ways to Make a Model.—The way in which you get your model made depends on several things and over these you will have little or no control.

There are two ways for you to get a model made of your invention and these are (1) to make it yourself and (2) to have a model maker make it for you.

These two general ways may be further divided into several sub-ways and among these are (a) for you to have your own workshop, or laboratory and hire machinists, or electricians, or chemists, and have them do the work under your direction; (b) for you to give a model maker the job and have him, or his men, do it under your supervision and (c) for you to have separate parts of it made by various model makers and then assemble them in your own shop.

If you are a little skilled in the use of tools there isn’t anything I know of that will give you greater pleasure than to make each part of your model with your own hands in your own shop and watch it grow day by day until it becomes in truth the very apple of your eye. At least that is the way I feel about it. Moreover it gives you a sense of security you cannot have when the work is in some one’s else hands.

In making a machine from your own ideas and plans no one can do the work so well as yourself provided you can do the work at all and besides it is cheaper and far more satisfactory.

Should you have a fat pocket-book and at the same time a taste for inventing and the sciences—these elements seldom go hand in mind—but if they should get close together in your case I say, the right way to make a model is to hire skilled men to do the work while you do the thinking and the assembling in your private lab. By this process your model will go forward rapidly and the work will be done in the best fashion.

Before employing any one to work on your invention have him sign this agreement:

EMPLOYEE’S PATENT AGREEMENT

The plan of having a model maker do all of the work under your direction may not appeal very strongly to you but after all, if you lack the skill and the equipment needed for making your model, it is a pretty good scheme.

Every large model making establishment has separate rooms fitted up where each inventor can work on his own machine and this gives you the privacy you demand and besides whenever you want a part made or changed you have a skilled mechanic at your beck and call and a shop equipped with the finest machine tools for him to use.

Nor need you be afraid that your invention will be appropriated, which is a high-toned name for theft, by either the model maker or his employers to whom you have entrusted your drawings, and for the following reasons:

(1) Because any hint of such a thing as theft would ruin his business for all time; (2) because 99 per cent. of all inventions fail to make money for any one of 99 reasons and (3) because the model maker grows rich making models for inventors while the latter mostly go broke; and as far as the employees are concerned we must grant that they are as honest, or even more so, than the average run of suffering humanity.

Neither are inventions apt to be stolen by patent attorneys for the reasons cited above but after you have worked out your invention, built a model and obtained a patent you are then in great danger of being separated from the fruits of your genius and perseverance by the professional promoter who makes it his business to finance the invention and at the same time to feather his own nest; but more about him a little later.

A good way to safeguard yourself at the hands of model makers, if you have any doubts about them, is to give different model makers different parts to make and then assemble them yourself. While it takes considerably longer to build up a model in this secret way still there is a lot of satisfaction in this method of procedure.

The Tools You Need.—To make a model of any description you need the usual tools that are the handservants of every jeweler and machinist, see Fig. 68, and you ought to have a small drill press, see Fig. 69, and a screw cutting lathe, as shown in Fig. 70, if you can afford these machines.

There are two or three tools that nearly everybody knows about and yet which very few folks know enough about to use them. One of these tools is the vernier and another is the micrometer and both are used for precision measurements.

The vernier is not, strictly speaking, a tool in itself but it is a device that is applied to scales which makes it possible to measure small fractions of an inch much more easily and accurately than can be obtained with the scale alone. The vernier is also used on calipers, micrometers and other tools and instruments.

The vernier is a short scale which is fitted to and slides along the edge of a fixed scale as shown in Fig. 71. The fixed scale is divided into 10ths of an inch and the vernier, which is ?/10 inch long, is divided into 10 spaces.

Suppose now when you measure a part of your model that you move the vernier over to the right so that the first mark of the vernier and the first mark of the fixed scale are exactly in a line with each other, then the vernier will have moved just ¹/10 of a scale division which is ¹/100 of an inch.

If the record marks of the vernier and of the fixed scale are exactly even then the vernier will have moved ²/10 of a scale division or ²/100 or ¹/50 of an inch, and so on. The fraction of the ¹/10 inch that is obtained with the vernier is added to the number of inches and the fractions of an inch of the part which is measured. The vernier gets its name from Pierre Vernier who invented it in 1631.

The micrometer is a tool, or instrument, which will measure accurately from 0 to 1 inch in thousandths of an inch. It is one of the most useful measuring devices that has ever been invented and if you are to build a model accurately you cannot get along without one. It is shown in Fig. 72.

There are five parts to a micrometer and these are (a) the frame; (b) the anvil; (c) the spindle; (d) the sleeve and (e) the thimble. The frame is held in the left hand, the object to be measured being placed between the anvil and the spindle; the thimble is turned by the thumb and finger of your right hand and the spindle, which is fastened to the thimble, turns with it and moves through the nut in the frame until the end of the spindle touches the object to be measured.

The measurement of the object is shown by the vertical lines on the spindle and the horizontal lines on the thimble and both of which are numbered. They are really a form of vernier.

To read the micrometer, that is to find the measurement of an object, you have only to multiply the number of vertical divisions which you can see on the sleeve by 25 and to this add the number of divisions on the bevel of the thimble from the 0 line to the line which coincides with it, that is, comes even with the long horizontal line on the sleeve. It is easy to learn to read a micrometer by taking one in your hands, making a few measurements and following the above instructions.

The wire gage is a circular piece of flat steel a little larger than a silver dollar and it is used to find the numbers of, and to measure the sizes of, wires. There are 32 slots cut in the edge each ending in a hole and numbered from 5 to 36 as shown in Fig. 73.

To find the number of a certain sized wire slip the latter into the slots until you find one into which it will just pass snugly and the number of the slot will be the number of the wire. On the reverse side of the gage will be found the sizes of the wire in decimal fractions of an inch.

There are a number of different wire gages but the American Standard or Brown and Sharpe, or B and S as it is called for short, is the one mostly used by machinists in the United States.

Other useful gages are for the measurement of wood and machine screws; for finding the pitch of screws; for measuring the inside of tubes, holes, etc., and for measuring the outside of rods, tubes, etc. These tools and all others used by jewelers and machinists can be bought wherever tools are sold.

Buying Materials.—Many inventors waste time and sacrifice accuracy in making, or trying to make, wheels, gears, threaded rods, nuts, binding posts, contact points, switch levers and blades, hard rubber knobs, handles and other parts.

Now all of these things and hundreds of other parts can be bought ready made of model makers, gear works and dealers in hardware, model aeroplanes, electrical and wireless apparatus. And before you begin a model of any kind you should get catalogues from all of the supply houses you see advertised. Fig. 74 shows quite a number of parts you can buy ready made.

About Making Patterns.—Very often though you will have to make a special part out of metal or have it made. Like everything else there is a best way to do this.

Suppose you need a standard something like that used for a telegraph sounder, as shown in Fig. 75. To saw and file out a solid piece of brass would not only take a long time but it would prove a very tedious job; and this is also true of many other parts you will need in the course of making your model.

The best way is to make a pattern of wood of the desired part, take it to a brass, or iron, foundry and have it cast. It is easy then to smooth it up with a file or to machine it in a lathe, or shaper, and lacquer it when it will look like a mechanic’s job.

It is nice and easy work to make a wood pattern, that is to cut out of wood the needed part of exactly the size and shape you want the finished casting to be. The wood for your pattern should be pine or poplar and thoroughly seasoned. A scroll saw frame will come in handy for sawing out small patterns.

Where two pieces of wood are to be fastened together a good glue should be used. After the pattern is built up file out the uneven places with the kind of files made for scroll-sawyers’ use. When this is done smooth up the pattern with medium fine sandpaper and finish it with very fine sandpaper.

Should any holes or cracks show in the pattern after it has been sandpapered fill them up with putty; and, last of all, give the pattern a couple of coats of shellac varnish or rub graphite into it all over to keep it from sticking to the mold. Your pattern is now ready to be cast in metal.

A pattern, if it is complicated, should be made by a skilled pattern maker for it must be made in a certain way so that it will draw from the mold easily and without injury to the latter and leave it perfectly smooth.

Casting in Iron and Brass.—Somewhere above I said that a pattern should be the exact size you want the finished casting to be but as a matter of precise statement iron, brass and nearly all other metals shrink when they are cooling and so the pattern must be a trifle larger than the exact size you require and you must also allow for filing and machining. (See Fig. 76.)

As iron shrinks about ¹/10 of an inch to a foot, brass shrinks ? of an inch to a foot and steel and aluminum shrink about ¼ inch to the foot you must allow this much for shrinkage in making your patterns. Type-metal is an alloy which expands on cooling and this is a useful thing to know. You will find a formula for making it in Appendix L, and all of the appendices from A to N contain detailed information on a variety of subjects that should be very helpful when you are making your model.