Restoration of a miniature ivory pocket watch

	Once the teeth were cut the barrel was partially hollowed out.
Then. it was parted off with a jeweler's saw and reversed. When held in a wheel chuck the flat side was faced off using a slide rest.
	After checking that the teeth were running true the pivot hole was drilled and then bored using a ball burr and slide rest.
Again the piece was reversed. The inside was finished and the undercut that holds the lid was formed.
When the barrel and train wheels were in place, I was delighted to find that the train ran freely and seemed to operate as smoothly as in any more usual watch.	Now, with re-assembly of the remaining parts, the watch would be going again, or so I thought.
The photo shows the finished barrel with a brass lining next to the old barrel. The hook is an integral part of the lining.
	The barrel lid was fitted and the hole was bushed and re bored to assure that the barrel would run true and upright on the arbor.
With a properly proportioned mainspring in place, it seemed a simple matter to complete the job.
	As with so many mechanical things we take for granted these days, the simplicity of operation is often suppositious. A recent presidential candidate often was quoted as stating that the devil is in the details. So it is with the ivory watch.
When assembled the ivory watch began to run immediately after power was put to the mainspring. Considering the nature if this particular watch there would be no great demand for accuracy but I felt that it would be important for the watch to run completely down. If it did not do so, the constant force of the mainspring bearing on the single tooth of the barrel against the center wheel pinion over extended periods of time might cause deformation or failure. Therefore it is important that the watch run with a minimal amount of power on the train. Things looked really good initially so I went ahead and fully assembled and cased the watch. The watch did not continue to run during the first test when completely assembled. It did not take long to determine that the minute wheel was seriously binding. Further examination revealed that the dial, when pinned firmly to the movement, was pressing hard on the minute wheel. There were also some unexpected deepening problems. The minute wheel was deputing properly with the cannon pinion but was too close to engage the hour wheel properly. This rather strange situation suggests that the minute wheel, hour wheel or both may have been substituted for that which worked properly at one time. I thought it to be the minute wheel since it was also too tall. These parts are easily lost when the dial is not in place. Regardless, I shortened the minute wheel appropriately and rounded up the hour wheel to give the proper deputing. That cured those ills and let me get on to discovering the others. At this point the watch was running but was gaining time at the rate of fifteen minutes per hour. It also had a tendency to stop occasionally, which, as I mentioned, was intolerable. The motion also was not good. The barrel and the trains of wheels were running freely now. I wanted to call Paul Harvey and ask him to reveal the rest of the story. A watch is not the simple machine that it seems to be. Hundreds of years of development and much science are involved in its proper function. When someone with great skill endeavors to create a curiosity by reproducing brass parts from ivory, much is revealed. I will not attempt to provide in depth technical explanations here but rather comment on some cause and effects revealed by Mr. Holton’s watch. The difficulty begins with the substitution of the balance wheel with one of ivory. Since ivory is much less dense than brass it produces a wheel that is much lighter and has less inertia. This inertia is carefully balanced with the stiffness of the balance spring. In order to cause the ivory balance to oscillate at the same rate as the original balance a much weaker balance spring must be used. Let us suppose that Mr. Holton fitted his balance with a much lighter hairspring so that it would keep reasonable time.	When Mr. Holton installed this ivory balance, I would bet he discovered that the watch would not run. The new ivory balance and hairspring lacked the force necessary to operate the escapement adequately. Mr. Holton, I believe, was able to understand the problem and added weight to the ivory balance by inserting six small lead weights into the balance. This was accomplished by drilling holes into the rim from below and gluing in the weights. Small brown spots appear on the balance rim as a result of this process. Maybe the glue reacted with the ivory (See the photo above). The pallet stones were adjusted by someone previously to reduce the draw in an attempt to get to get the watch to run reliably without stopping on the lock due to the weak balance spring. This situation left the guard pin in contact with the roller often and hampered the balance motion. Still, the watch was gaining at the rate of fifteen minutes per hour. I guess that a stronger hairspring was used at some point in order to improve the reliability sacrificing timekeeping in exchange. Maybe the watch never really kept time. As you can see now, the problems of an ivory balance were now mine to ponder. With the addition of another half dozen weights to the balance wheel, the rate was slowed to a gain of a few minutes per hour. After a number of adjustments to the pallet stones the watch had enough draw to improve the motion and still unlock fairly well under the force of the hairspring. Although still gaining some time, the watch was running well and completely down. I decided to leave well enough alone. After all, it is a novelty watch. But another surprise was waiting. During one of the follow-up test runs the watch stopped prematurely. After a couple of exclamations I began to examine the watch. I discovered that the barrel lid had come loose and was binding the barrel. As I had suspected previously, the Ivory barrel wall had expanded. But this time without the help of the mainspring the lid itself had pushed it open. Obviously there would need to be another design change. Ivory will not substitute for brass without some modification to the design of the barrel. The only course I could conceive that would allow the watch to run reliably was to make the entire barrel lid from brass and have it enclose the barrel wall instead of wedging inside. This would have the benefit of countering the forces of the mainspring and capturing the ivory between the two metal components. Since the lid does not show when the watch is assembled I felt this change was acceptable in order to solve the problem. Mr. Holton was, no doubt, a fine craftsman. The fact that his watch is running after a century is very satisfying. I found a considerable amount of discovery following in his footsteps. It is unlikely that anyone will be as inclined to produce a watch from ivory in these times. If they do, however, they would do well to consider the shortcomings of the material and select a design that will compensate for them.