Jacot tool

[arron]

Thank God it's Friday (i seem to be saying that more often as i get older and have less energy).  I hope everyone is doing well.  I hope that etiquette-wise it's ok for me to start a new post put forward somewhat differently than a previous post i made that didn't get much love  . 

I am a bit disappointed in the new  jacot tool i bought because although it is a complete set, the spindle on the right (red arrow) isn't large enough to hold any of my PW wheels other than the balance and  escapement.  I tried both sides of the spindle.  The spindle on the left (yellow arrow) is also too small, but i'm thinking that might be ok since the left pivot will simply ride on top of the groove in the spindle.

Question: So if that is the case, how are folks polishing the pivots on the larger wheels.  Are you using a lathe or some other procedure/tool.  I appreciate any information that can be provided.  Have a good weekend.

[oldhippy]

Here you go have a look at this video. It's from our good member JDR. Don't expect to get things perfect first time there is an art to pivot polishing and burnishing, like all things new it takes practice.

 

 

 

[nickelsilver]

Jacot tools should have the runners marked in pivot size, some have arbitrary numbers but most will be marked in metric. So if you want a 0.12 pivot, you put the part in a 0.12 bed (bed is the grooved part of the runner). Unless- you are starting with a larger pivot, say 0.15, then work your way down, from bed to bed. Some tools will make exactly the size pivot marked, some will make a pivot that fits in that size jewel (a slightly smaller pivot). The size is dictated by the depth of the groove, so when the burnisher will no longer cut, the pivot is level with the top of the groove.

 

Conical pivots should be set so that only the cylindrical portion is in the bed. Square shoulder pivots, bring the bed right up to the shoulder. On the pulley side, the runner is a simple female cone, and it works with the tip of the opposite pivot. As long as the tip gets in there it's ok. Yours looks fine to me.

 

Most sets will do pivots up to around 0.35mm. Larger sets will go up to 1.00mm or so. In the pic you can see a typical small set (upper) and large set (lower). The larger set, with it's "center wheel runner", also has a corresponding pulley-side runner with larger female cones.

 

Keep in mind that burnishers are "handed". Way back in the day when the designation came about, they were typically used in the right hand, on the underside of a pivot spinning in a lathe. For a Jacot, right hand, the burnisher is on top of the pivot, so the opposite burnisher is needed. So- for right handed Jacot use, you want a left-handed burnisher, which is French is gauche, or G. The most commonly used one is from Bergeon, the 2933-G. The burnisher is slightly parallelogram shaped, as you can see in the pic. If you have the wrong one, the side of the burnisher will hit the pivot shoulder, and the cutting face won't touch the whole length of the pivot. The Bergeon and many others from the past have one edge with a radius, the other straight for the pivots as needed.

 

 

 

 

 

Edited March 12, 2022 by nickelsilver

[KarlvonKoln]

Using the stop/rest can help somewhat with larger pivots, but it is not meant to work in the groove there.  It works best when the rest-portion is mounted at the very end, resting against the face of the end of the runner.  This also puts it out of the way of the work you are doing.  I'm going to try putting a link in here showing what I'm referring to. In the thread below they call it an end guard, but for me it seems to function more as a "stop rest".

https://mb.nawcc.org/threads/jacot-tool.120913/

[arron]

Thanks guys, that's all very helpful.  Apparently I have the small size pulley-side spindle.  Based on my internet search I am guessing that finding a larger stand-alone spindle would be exceedingly difficult.  nickelsilver, what do you think about drilling out one side of the spindle to accommodate larger pivots sizes.  I wonder how I'd smooth out the new hole so that the pivot doesn't get damaged.  Do you have any thoughts on that?

[nickelsilver]

How large of a pivot do you want to fit? Do you have a runner with beds large enough?

 

If you need to open one side of the simple runner, it's a little tricky. Assuming you have a lathe, you still need a cutting tool to cut the cone. I would make a simple 3 face cutting tool from carbide but I have the grinder for that. Maybe try to find a 90 degree carbide spotting drill? As I recall Steiner used 90 for their cones so should be a good choice. A regular drill tip isn't angled enough.

[arron]

Right now i have pivots sizes .4 mm and .8 mm.  I don't think they fit correctly in the runners with beds, but i figured for some light polishing they would sit tall in the bed and could be worked on in that way; although i don't know if that then puts the pivot at an angle and makes it harder to keep cylindrical.  

The drilling of the spindle sounds a bit more technical than i have the aptitude for and i don't want to ruin it.  so i think for now i'll try my lathe and then some day i might find a larger spindle or upgrade my entire jacot for one that comes with a larger spindle.

Thanks nicklesilver.  Arron.

[nickelsilver]

Yes, if you put too large of a pivot in a smaller bed it will sit high and at an angle.

 

Since you have a lathe, it's pretty simple to make up a whole new single runner. They are often a nominal metric size, then reduced along a length for the pulley. You can make the cone by simply cutting it with a sharp pointy hand graver. For occasional use it doesn't even need to be hardened. But if your beds are too small it's kind of moot.

 

A workaround, and a good one, is to make a half-runner that fits your lathe tailstock. It can be as simple as a piece of wood dowel, or you can use brass. Drill it the size of your pivot, file it down so the drilled area is exposed, now you've made a "bed", grab it in a drill chuck in the tailstock. Chuck one end of your part in a collet in the headstock, and rest the pivot in the bed. Now you can use a pivot burnisher or file safely without stressing anything. I knew some old clockmakers who only worked pivots like this and they did very good work. After a while you end up with a collection of beds and don't have to make them anymore.

Edited March 13, 2022 by nickelsilver

[arron]

That is an excellent idea. Thank you very much.

[goran]

@arron, I have the opposite problem. I missing the shaft with beds size 4-16 (0.04-0.160mm). I have other shafts with sizes all the way to 1.2mm. Bigger sizes are for clock work and I am not planning to work on them. Let me know if you are open for exchange.