I recently was working on a late 1700s watch that was missing a ratchet wheel for the fusee and it’s retaining screw. There was also some damage to the locating pin and a lot of scratches on the surface the wheel would have sat on. The damage needed repairing and the wheel and screw replacing. You can see in the drawing below the wheel would be just 8.7mm in diameter - quite a challenge!
The first thing to do was take several measurements of the existing parts. The position of the ratchet clicks to decide the size of the wheel, and the location and size of the screw hole and locating pin. Using a CAD drawing helped me in making some decisions based on the inner and outer dimension of the teeth, as well as a tooth count to make sure everything seemed in proportion before cutting any metal.
Taking measurements on the Hauser meant I could also remove the locating pin and drill a locating pin hole at the same time. Once this was done I held the fusee in the lathe to skim off the smallest amount of material from the surface. I only wanted to ensure the surface was flat, so essentially removed the ‘peaks’ formed by the scratches while leaving the deeper grooves (not pictured here)
When making wheels it’s not much extra work to make more than one, so below you can see I’m actually cutting four. This will mean that if there are any issues cutting the locating holes I won’t have to start from scratch! These were cut from some flat brass stock slightly over thickness with a central hole slightly smaller than would be finally required, then turned in a lathe to the correct outer diameter.
Once the teeth were cut they could be separated for the locating holes to be drilled. While setting this up, the Hauser Microscope can be used to inspect the teeth - they had some small burrs from the cutting process which would be removed with a bristled brush, but the form was as it should be.
The last task was to make the locating pin and a screw to hold the ratchet wheel down. As height is at a premium inside the fusee the screw and accompanying hole need to be countersunk and so I made a jig to hold the screw to make it match the hole countersink for a perfect fit. The top of the screw head had a very slight dome, in keeping with the style of the watch.
As you can see when everything is assembled, it’s a very small wheel indeed, but looks (and most importantly, functions) great. The watch is now ready to run for a few more hundred years! In keeping with conservation practice, the wheel is engraved on the reverse with initials and a date to make it clear that this is not an original component.