Show me the business end of your Jacot tool

[ic0n]

I bought a Jacot tool some years ago for a project, and discovered that it was partially broken. What would be the 'headstock' on a lathe had sheared off, but it took me a while to realise this, which caused much puzzlement as to how the tool was supposed to work. I brought it out again recently and had a better look at it, and realised what the problem. I've made a guess as to how to fix it, and would welcome your thoughts. This is the bit that was broken:

The little rod had sheared off flush. I drifted the stump out into the groove helpfully provided - which makes me think that this is not an uncommon occurrence. From memory, the rod's about 1.2mm.  I drilled a small hole in the end of a bit of pivot steel, but I had to guess how long to make it, how deep to drill and what what diameter. You can see what I came up with. Then I looked at the pulley and drivers, which I really don't understand. There are two little brass taper pins rivetted into a carrier, held in place with a cover plate.

 

 

The cover plate has holes which look deliberately placed, but for what reason I don't know. With some 'fettling', I can now slide the pins in out - about 3mm!

This is the business end now. Does it look about right?

 

 

 

 

[nickelsilver]

That's a very early example, and someone has adapted a pulley to it. Originally the pulley would be clamped to the part itself, and turned with a bow. Later versions have the pulley as part of the headstock, with a screw adjustment to position it so the drive finger makes proper contact with the wheel.

 

If you need to work on a part that doesn't have a wheel, like a bare balance staff, you use little fish-shaped clamps that can be driven by the finger. In the pics you can see the headstock end of a modern tool, the knurled knob at the far left moves the pulley along the headstock runner for positioning. The runner is a simple bar with concentric V pip in the end for the pivot to ride in. There are different sizes for different pivots. In the second pic are more traditional yet still "watch size" drive dogs, some clamp-on drive pulles, a set of the "fish" with the tool to open them, and some other drive runners (top of pic). Those have slightly tapered shafts and are to hold parts with holes through them. The ends are female cones and they would be held in a dead center lathe; these are useful for working on hour wheels for example- but nothing to do with the Jacot.

 

 

[ic0n]

I think the pulley is original - a wider shot shows the widget for moving it to and fro. The case has a cut-out for these bits, so I'm thinking it was made like that?