This weeks post will show you how to replace a missing roller jewel. This is one of the toughest jobs that I ever need to do. This is a very precise job, close just doesn’t count here, it is either perfect or the watch won’t run properly.  Part fit is critical and the roller jewel is very small and almost impossible to hold, overall not an easy task.  This is the part of the job where you just need to practice over many years and patience is the key.

First lets give you a brief idea of what a roller jewel is and what it does.

How the Escapement Works

When energy is stored in the mainspring, by winding, the train wheels begin to turn. This energy is carried from the barrel through the center, third and fourth wheels to the escape wheel.

Considering the escapement as a unit, it can be seen that the escape wheel supplies the power, whereas the pallet transfers the rotary motion of the escape wheel into a back and forth motion of the pallet.  The pallet in turn imparts motion to the roller jewel which causes a vibrating motion of the balance wheel.

Tools used

To replace a missing roller jewel, you need just a few tools.  First this pair of balance holding calipers. You need an alcohol lamp and then shellac to hold the jewel in place.  Shellac is an interesting substance.  It is hard and brittle in its basic form, but when heated it melts and flows into small spaces, then goes back to hard substance when it cools.  It is the basic material that holds jewels in place on the balance and Pallet.

Balance holding calipers
Alcohol lamp

The picture below shows the balance wheel of a Hamilton 992b that is missing the roller jewel.

Next job is to try and find a roller jewel to fit.  Most people would think that I just snap my fingers and go to some assortment and find just the right part to fit.  All those people would be wrong.  Here is an assortment of jewels, all sizes and shapes just waiting for me to go through each and every one, one at a time to test fit into that small opening to see if it fits!

The toughest thing about working with jewels is they are very small, slippery and hard to hold. They bounce very well, are non magnetic and if you drop one, they are just about impossible to find. You now go through every jewel, and pick it up, try to fit it into the small opening in the roller table.  Here is where my saying “close does not count” comes into play.  You have NO leeway in this job, it is either the right length, width and thickness or it does not work. Keep in mind that the escapement is the heart of the watch. You are dealing with clearances about the thickness of a piece of paper, so it has to be just right.  No room for error and practice makes perfect.

Once you are lucky enough to dry fit the jewel into the hole in the roller table, now comes the alcohol lamp and shellac.

Alcohol lamp heating the balance

If you notice from this picture, the alcohol flame is on the end of the caliper and will never actually touch the balance. You heat the end, the heat travels down the length of the holder and heats up the balance wheel. You never want to put a flame on the balance or hairspring, that would be a disaster. After the balance is hot, you carefully touch a piece of shellac to the underside of the jewel and let it melt into the roller table.  The shellac only stays in its melted state for a few seconds, so now you need to carefully adjust the roller jewel so that is is the right height, not leaning left, right, forward or backwards.  This process normally takes 4-5 tries until you get it just right. When you think you have it correct, you remove the balance wheel from the calipers, let it cool and reinstall in the watch to see how it works. If the jewel is not adjusted correctly, you start over, back to the calipers, heat it up, adjust and repeat the process until it “just right”. No time frame here, it might take 15 minutes or 2 hours, you repeat until it works!

Jewel installed, centered and straight


Shellac that is used for the roller jewel replacement

Size of a roller jewel

To give you some idea of the size of a roller jewel, the picture below shows the jewel in the center, on the left is a small second hand from a mans watch, and to the right is the tip of my thinnest oiler.

This is one of the toughest, but most satisfying jobs that I ever do. On one hand, it is time consuming, has a high frustration factor, lots of time doing the same task over and over until it is done.  But once it is finished and the watch is running, you know that you have accomplished a job that not many people can do, that feeling of satisfaction is why I love this job!!