Identify this tool!

[Rdot84]

Good morning fellow enthusiast,

 

I bought a lot of tools and this is one of the pieces that was included. Given my level of inexperience I have no idea what it is. Please educate me 

 

[nickelsilver]

That's a balance screw undercutter, used to remove weight from balance screws when poising. This one is probably for a limited range of pocket watch sizes; there are tools with 6 or more cutters to accommodate a larger range of screw sizes.

[luiazazrambo]

I would love to see it in action.

[nickelsilver]

5 minutes ago, luiazazrambo said:

I would love to see it in action.

It's pretty simple, you take out a balance screw, insert the thread into the hole, then turn it with a screwdriver to remove a bit of metal from the underside of the head. Well, simple as long as you don't break the screw unscrewing/ screwing it, don't lose it, and don't take off too much weight, hahaha.

 

This one has two cutters but they are double ended, they can be flipped around giving 4 sizes of cutter.

Edited December 10, 2020 by nickelsilver

[Rdot84]

Thank you @nickelsilver! I got the other style as well in that lot which unfortunately is in rough shape and has a broken cutter. I was just thrown off by this one because of the screws on the sides. Made me feel like something was to be mounted to it? 

 

[praezis]

I wonder what such "treated" screw does to the balance wheel thread - It will have an unthreaded part then!

Frank

[luiazazrambo]

As far as I understand the thread wont be touched as it slips in to the hole, only some material will be removed from the head.

[luiazazrambo]

So it is using the same principle like this one:

but this one - as far as I know it - was used for pocket watch bows and to create a shoulder for bigger screws than balance screws.

[nickelsilver]

These tools can indeed bugger up threads, as they were often roughly made. More of a problem with gold balance screws. With a bit of care and some deburring around the inside of the hole though they do work. Same principle as undercutters for chronograph screws, though the main intent of the balance undercutter is to cut inside the head, leaving an invisible retouch and the chrono screw cutter cuts the whole underside. In reality the balance cutters almost always touch the entire surface. In both instances I prefer to use a lathe, with a cross slide, and know exactly how much material I have removed.

 

The pocket watch bow cutter above is on a similar principle, but can form a pivot on a raw bow or reduce the pivot size on an existing bow. I've owned one of the pocket watch cutters since I was in school, and I think I've used it once or twice haha. But it really is the easiest way to put a pivot on a bow.

 

This type of cutter is called a fraise a pivot in French, pivot cutter.