Well it's really more tool maintenance than repair. It's a much overlooked part of the trade. Probably any trade.
You can't do quality work with crappy tools. Slip with a screwdriver across the back of a 19th century carriage clock and leave a crater of a scratch, and then what do you do ? Even if you don't slip you will more than likely botch up the screws like this.
Seems like hammers should be a rarely used tool in the delicate world of watch and clock repair, but in fact they are used on a daily basis. Many times. These are steel hammers, but leather hammers are also used frequently.
The issue with hammers is that whatever you hit with it, especially when flattening something, or setting a bushing in a plate, whatever marks, dents or imperfections on the face will be transferred to the item.
Here's two of them I did today. Larger one still has a few scratches in it that were very deep, but will eventually come out. You don't want to remove any more metal than you have to.
This is the face of a planishing hammer. I think it's almost 100 years old.
I forgot to take any before pics of these two tools, but although they weren't as bad as this one, they weren't far from it. Zoom in on the end of that and imagine the marks it would leave.
One think to mention is that all of the work on these tools was done by hand, with other tools, that also have to be maintained from time to time. The hammers were done starting with a diamond surface plate, and then progressive grits of sandpaper starting at 320 and ending with 2000. There is no polish or buffing on these finishes.
These are just some of the hammers in my drawer.