The Gear Train would be the last area for us to learn about before the looming Gear Train exam. The exam mainly focuses on the Gear Train, specifically End Shake and Trueness of the wheels, but also assesses the cleanliness of the movement and the lubrication of the Keyless work amongst other things.
What we were about to learn, like everything we have learnt so far, was very important not only for the exam but also for the rest of the course and our futures as watchmakers. The basic skills we are learning, using the 6498, will be transferred to any calibre that we ever get the chance to work on so its crucial to have a good understanding of it all.
Our first focus would be checking and adjusting Train Wheel End Shake. End shake is the amount of vertical movement the arbors are allowed between their two bearing surfaces and is generally proportional to the size of the pivot in question. Jewels in wristwatches act as bearing surfaces for the pivots of each wheel. Basically the wheel has an axle, in the form of the arbor and pivots, the axle allows the wheel to ride between the two jewels. The wheel needs to have some freedom of movement (or endshake) to allow it to rotate freely but not so much as to keep it from lining up with the next wheel when the watch changes position.
The train wheel end shakes are generally between 0.01mm-0.05mm and should measure in a wedge shape, decreasing in size as you move from the centre wheel down to the escape wheel. On the 6498, the Centre Wheel should have approximately 0.03mm, the Third Wheel should have approximately 0.02mm, the Fourth Wheel approximately 0.015mm and finally the Escape Wheel gets the least at approximately 0.01mm.
We would need to understand what the correct endshakes of the train wheels look like and how to achieve them. Getting a feeling for what these endshakes look like is just as important as learning how to actually adjust them, especially as in my experience the Horia jewelling tool isn’t always precise. In order to adjust the endshake for a particular wheel we move the jewel up and down in the plate. The jewels in modern watches are held into place by friction and can be moved up or down, this wasn’t always the case with older watches. A jeweling tool is used for installing frictioned jewels and for adjusting the endshake.
The Horia jewelling tool uses a variety of stumps (the bottom part) and pushers (the top part) for different sizes of jewels and the movement of the pusher can be controlled with the micrometer adjustment on top of the tool. To move the jewel you turn the micrometric feed on the top and each mark on the scale represents approximately 0.02mm of vertical movement. The tool allows jewel adjustments to be carried out quickly and extremely easily.
The correct end shake must not only allow the wheel enough freedom to turn but also allow it to line up properly with the pinion and wheel that its wheel and pinion interact with. All the wheels in the train interact with each other so it is possible to make what you believe to be the correct adjustment, only to find that everything doesn’t line up properly. The only solution to this is more adjustment, initially its common to find yourself moving from wheel to wheel and back again searching for the correct combination. As always though, practice makes perfect!
Adjusting End Shakes in progress…
Our next focus would be checking the Train Wheels for trueness and learning how to true them. Truing wheels shouldn’t really ever be necessary unless you are making a watch from scratch or trying to rectify accidental adjustments performed by another “watchmaker”. Unfortunately, due to the thinness of most train wheels, its not uncommon to come across such accidental adjustments.
Absolute trueness of the power train wheels is necessary to ensure smooth power transmission and isochronism. Isochronism is the ability of a watch to maintain consistent time regardless of the influences around it. In order to check if a wheel is true, it must be placed in a Truing Calliper/True Poise Tool where it can be rotated while comparing its rim to a fixed arm on the tool. Corrections if required can then be made using the same tool.
Bergeon Truing Calliper…
To true a wheel, its placed in a Truing Calliper/True Poise Tool and slowly rotated while comparing its rim to the edge of a fixed arm on the tool, minor corrections can then be made to the spokes or the rim of the wheel in order to bring it to perfect flatness. The corrections are made using a piece of peg wood, a small amount of pressure is applied to the area to be corrected and the process continues until the wheel is flat and true. Small discrepancies can easily be spotted with some practice and with even more practice they can be fully corrected. As with watchmaking in general, masses of patience is required because initially you can find yourself chasing a bend around the wheel for hours!
The last part to learn was correct lubrication of the train, we would need to know the correct oil to use for each wheel and what the correct amount looks like. Applying the correct amount of lubrication to the power train of a watch is something that really can only be learned from experience. While any amount of lubrication, from barely anything at all to a jewel swimming with oil, will probably perform adequately in the short term, the long term performance of a timepiece relies on precisely located amounts of lubrication. The lubrication must be applied with great precision and the jewels must be of the highest cleanliness.
The Lubrication Tools…
Probably the best way to see if a pivot has the right amount of oil is to remove the train bridge and inspect the underside of the jewel. A clean looking “doughnut” shape of lubrication which is of the appropriate size in the middle of the jewel is a good indication of getting it right. The problem with this method is that once the bridge has been removed, the jewel and pivot must be cleaned of any remaining oil before the bridge can be reinstalled and the pivot lubricated again. The only real way to check is to use a strong eyeglass or microscope to see how much lubrication is sitting in the oil sink of the jewel, this is normally a good indicator of correct lubrication.
Diagram of a Jewel showing the Oil Sink…
After lots of practice, you begin to understand how much oil on the oiler translates to the correct amount of lubrication. Larger jewels are obviously easier to oil because there is a bigger area to place the oil and its size means you can see the lubrication more easily. The tiny escape wheel jewel can be tricky the first few times due to its minuscule oil sink. After practice after practice, I could confidently leave a bridge in place with the knowledge that I had applied the correct amount of lubrication, for the watch to run smoothly for many years to come, without it running down the pinion leaves or transferring onto other nearby surfaces.
I was now in the position of being able to fully service the whole 6498 movement minus the escapement which would be our next focus after the Train Exam. Lubrication and End Shakes are fairly easy after lots of practice but truing wheels can be a real lottery at times. The bend is either corrected really quickly or it takes ages and the wheel still isn’t perfectly true afterwards. Generally though I can achieve good results in a matter of minutes. The Train Exam is fast approaching but with my newly learnt knowledge and lots of practice completed, with still more to come, I’m definitely ready for it!