The Point of a Pin

Copyright © 1975, 2004 by Davis Multimedia, Int'l. All Rights Reserved.
As Printed in Sept./Oct. 1975, Volume 1, No. 2 of The Engravers Journal.

     In 1935 it was decided by the Gorton Machine Corporation to attempt a dramatic demonstration of the extreme accuracy built into Gorton machines which could be understood and appreciated by the non-technical as well as the technical mind. It is true that the 300 characters which make up the Lord’s Prayer had been printed in characters so small that a magnifying glass was necessary in order to read them; they had been cut on a single slug of type and had also been engraved by hand on the head of a pin. But such work had never been successfully done by machine.
    Below is their account of their attempt to do this same engraving on the point of a pin. The head of an average pin is approximately 100 thousandths of an inch (.100" or 1/10") in diameter. The point is approximately 5 thousandths of an inch in diameter (.005") or about twice the thickness of a human hair or one sheet of cigarette paper. This article tells the story of how this was done.
    The first step was to engrave the Lord’s Prayer in the correct design to fit into a circle and of a size which would be suitable for the proper reduction. This was done with the aid of standard Gorton copy type. The resultant master or pattern was a 2" circle in which the Lord’s Prayer had been engraved.
    Then a Gorton pantograph was taken from the production line and a few adjustments were made such as disassembling the machine and checking all ball bearings for size and roundness. Then the races were lapped. This was necessary due to the fact that ten ball bearings (eight of the manufacturer’s and two of the conventional radial type) are required to transmit the movement from master copy to cutter point and work, and an error so small as one-tenth of a thousandth of an inch in only one of the bearings would be sufficient to distort the entire engraving so that the result would be worthless.



    The object of this test was to reduce the master copy of the Lord’s Prayer to as small an area as possible and still have it remain legible under a magnifier. The machine was set to reduce the original copy 400 times.
    The engraving operation was performed by the very point of the cutter and difficulty was experienced in keeping an edge on the point until after numerous experiments, when a comparatively blunt bullet-shaped point was adopted. The next problem was that of polishing the surface to be engraved smooth and flat to within one hundred-thousandth of an inch. Many materials were used – different grades of rough, face powder, diamond-tine, etc., but finally it was found that polishing with a fine kid leather produced the finest surface. The kid seemed to have just enough dust embedded in it for proper polishing action.
    The pantograph machine had to be insulated against vibrations set up in the shop floor. Although the machine was mounted on the concrete ground floor of their plant with wood block laid on top, the vibrations imparted from machines 100 feet away were sufficient to distort the engraving sufficiently to make it illegible. It was therefore necessary to use four rubber cushions 3" thick beneath the machine in order to eliminate this vibration.



    The weight of the operator’s hand was sufficient to spring the entire mechanism and so distort the minute letters of the finished engraving. The feed mechanism was therefore transferred to the table of the machine and the work was fed up to the cutter. It was likewise impossible to use an electric light to illuminate the work. Heat from this bulb caused enough expansion in the pantograph mechanism to shift the cutter point entirely away from the engraving with an hour after it had been correctly adjusted. For this reason night work was impossible. Likewise it was imperative that cold drafts be kept away from the machine as these caused contraction of the parts and would be as damaging as too much heat.
    An air-conditioned room was not available for this work and considerable difficulty was experienced with floating dust particles which would settle on the work and attach themselves to the cutter point. When this happened the cutter had to be taken out and the particle removed as it would bulk up so large under the microscope as to completely obscure view of the cutter point and work.



THE RESULT
    The result of this experiment was the complete Lord’s Prayer consisting of 300 characters engraved on the end of a platinum gold alloy wire within a circle of .005" in diameter. Two cigarette papers are approximately .005" thick. (Using the same size letters, the entire Bible of approximately 2,750,000 characters could be engraved within an area of 1/2" X 3/8". The complete Lord’s Prayer engraving therefore appears as a very faint speck on the end of the gold wire when viewed with the naked eye. The letters are so small in height (about .0002") that they must necessarily be engraved very shallow. In fact, the depth of each letter in the metal is only 1/40,000 of an inch. This depth is so slight that a mere rubbing of a finger over the finished job would be sufficient to obliterate it entirely or at least to make it unreadable.
    This lettering requires a magnification of about 175 diameters to read. For inspection of the lettering during the actual engraving process a smaller power glass was used for the reason that the cutter operating directly above the engraving made it necessary to mount the glass at an angle for observation, and at this angle the field of view was so small that only one line at a time could be focused.
    1. A 1/10" diameter piece of Sanderson’s Double Special Steel was used for the cutter. This is a water-hardening steel of extreme hardness capable of retaining a very fine point. The cutter was rough-ground to the approximate shape desired in a standard Gorton universal cutter grinder using a 35-80 Alundum BM wheel.
    2. When examined under a microscope, the rough-ground cutter showed a series of flats and irregularities around its circumference. These were removed by turning up and polishing using a small boxwood wheel about 1" diameter running at 1,700 R.P.M. this wheel was charged with pumice. During the polishing operation, the point of the cutter was held very lightly so as not to burn it.
    3. After polishing the point true, the cutter was placed in a polishing lathe where it was stoned very lightly with a natural Pike Stone to bring out the bullet-shaped point and to further sharpen the point. The stone used was held in a fine spring clip about 3" long, so that at no time was any stoning process, the point was repeatedly examined under the microscope in two positions so as to make sure it was true and not oval in shape.
    The Lord’s Prayer engraving described in this article is a permanent exhibit at the Lars Machine Inc. plant, and has been viewed by thousands of visitors from all parts of the world.

 

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