Most of the time I just swap out parts in watches. The past couple of weeks I’ve been working on a nice project watch. As a part of this watch repair I needed to make a new balance staff.
The watch is a Paul Breton. It’s a Swiss Bar movement from around the turn of the century. As it happens I can’t just call up Paul and get a new staff to replace this one with a bent pivot so I made one.
Since heat treating steel can cause it to warp the easiest way to cut a staff is to harden and temper the steel first. A balance staff is usually cut from blued steel. The steel is hardened to its “glass hard” state and then tempered to a springy state indicated by the blue oxidation on the outside. 
The tempering setup includes a dish of brass shavings and an alcohol lamp. The steel is placed among the brass shavings and slowly heated with the alcohol lamp until the blue color comes on the outside. The hotter we make the steel the softer it becomes. If we heat it too fast the outside will temper more than the center.
From the blued steel we cut the staff. It is important that the staff be perfectly concentric so we try and cut the entire staff without removing the steel stock from the lathe. Since we need the support to cut the very small diameters we work from right to left following the measurements we took from the staff and using the old staff as a gauge.
The pivots are left a little large because the final dimension will be attained through burnishing in the Jacot Tool. At each step the dimensions are verified with the components which fit on the staff. We check the hub to make sure the balance wheel fits tightly and that the hub is the right height.
We continue cutting the staff until we get to the other pivot. Notice that this staff has an unusual hour glass shaped hub between the balance arms and the roller table. Once the complete staff is cut we part it off and turn it around to make some final adjustments.
With the staff supported by the collet hub we make some fine adjustments to the roller cone so that the table slides down about 2/3 of the way. I also shape the pivot and take it down to about .02 or .03 mm larger than the final dimension.
Using the Jacot Tool (pivot lathe) the pivots are burnished down to their final diameter. The burnishing action serves to reduce the diameter and also to harden the pivot. You can compare the pre burnished look and the post burnished look here:
This is the final product: a beautiful watch.
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13 Comments
Wow. Awesome stuff! This is exactly what I’m doing in school right now. I just made a Jacot tool the other day to prepare for burnishing next week. Great post and nice work!
Very interesting post.
How much time did it take to make & install?
Hi,
I am not sure if you noticed, but on my web browser (IE7), the text is underneath the pictures 5 and 7 (from the top).
I did actually notice that. It seems to be an issue with WordPress. When I get some time I’ll try and figure it out. Hopefully you didn’t have a problem reading the article, it was plenty legible in Safari.
Well, I don’t do this often enough so the customer got a really good deal. I only billed for a couple of hours because I enjoy this kind of work and need to practice it to keep up my skills. The entire project from start to end took a full eight hours probably. If I did this more often I’m sure I could cut the staff, burnish it and install it in a couple of hours. One reason it took so long is that I wanted to go methodical so I didn’t have to make two. My first one worked! It’s been more than 3 years since I made my last staff.
Thanks for posting all the photos. I find this very interesting. I have a question. Maybe it’s just the photography, but it looks like there is a slight shoulder between the cylindrical portion of the pivot and the conical portion. Am I seeing this correctly? If so, what is the purpose of the shoulder? Thanks, and please keep these photos of repair jobs coming. They are very informative.
Vince, what you are seeing isn’t necessarily a shoulder but it is an imperfection in the conical portion. This is a result of my only having to make a staff every couple of years.
The cylindrical portion’s only purpose is to add strength to the staff so if it isn’t perfectly smooth it has no detrimental effect on the performance of the balance.
Great post J.Peter! Thanks for sharing.
What type of steel do I use to make a staff? It says blued steel, what about machinest steel? Where can I buy the steel? What percentage carbon? Someone said I can use sewing needles? Thanks.
I usually use MSC oil steel from MSCdirect.com and harden and temper it myself. The Bergeon blued steel for staffs is inconsistent and soft (pretty much worthless).
Hi Peter,
How do you tunr the part to the left of the balkance seat without removing the staff from the late?
I am struggling with this. It is too close to the headstok for me to get the graver in from the left as the angle always hits the collet and tailstock. Especially the left pivot. Yours looks as close as mine so how did you get around this problem?
I use a slot cutter ( a graver which can be inserted straight in) to rough out the left side of the staff but eventually you’ve got to turn it around to finish it up.
Hello:
I have tried several times to turn a staff (unsuccessfully)…. I would like to see photos of the actual gravers used. What face angle are they ground to? Do you grind the gravers down to present a smaller face/edge to the part? Would you hazard a guess as to the speed you run the lathe at while roughing the pivots? I have long said that I would be willing to pay for someone to produce a video showing the balance staff making process from start to finish.
Thanks,
Michael
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