Watches with broken balance staffs are eBay gold. Many hobbyists lack the skills or equipment to replace a balance staff or have been discouraged by a few bad attempts. As a result, watches with broken balance staffs get scooped up for cheap.
Becoming good at replacing staffs, beyond feeding your bargain hunting, will improve your watch adjusting. A new staff cures many adjusting ills, such as when pivots are bent or irregular.
This series of posts describes how to replace a balance staff. In Part 1, we’ll talk about some of the general issues. In the later posts, we describe how to disassemble the balance, remove the staff, stake the new staff, and fit the new balance assembly.
Change the Staff or Swap a Balance?
Before getting started, why should we replace the staff at all? Why not simply swap a complete balance assembly—wheel, staff, roller, and hairspring—from another watch?
We should replace instead of swap for many reasons:
- We should always aspire to learn new things and improve our skills. Staffing isn’t rocket surgery. Countless people have learned to do this well, so we can, too.
- It saves money. For the kinds of American watches this blog focuses on, balance staffs are plentiful and fairly inexpensive. Parts watches with good balances cost much more. For example, you can find balance staffs for an Illinois 16s Bunn Special for under $20, but you won’t find a Bunn Special with a good balance for under $100.
- Replacing the staff preserves the watch’s originality. For most vintage watches up until the 1950s, balance wheels are numbered. A watch with matched numbers on the balance and bridges will fetch more money when sold.
- Swapping rarely works because the parts aren’t truly interchangeable. The factory adjusters set up the escapement to match the wheel. The height of the pallet fork, length of the guard pin, depth and angle of the roller jewel, and many other factors were modified to make that wheel, roller, and hairspring run well in that watch.
Measure Twice, Staff Once
As in woodworking, in staffing we measure twice, staff once. The key to success in staffing is taking your time and measuring. Always measure: tools, jewel holes, clearances, and many other things.
Measuring adds many steps, but it greatly speeds up to process. We’ll point out things to measure throughout this series of posts.
Finding the Right Replacement Staff
Most of the success in staffing comes from picking the right staff in the first place; most of the rest comes from measuring it to ensure it fits.
You can buy replacement balance staffs in all the usual places. (Dashto is my first stop, for what it is worth.) The staff must match the movement caliber, of course, so you would first search the usual catalogs and web pages to identify the proper part number.
The first trap you might walk into is ordering the wrong pivot size. In the old days, most pocket watches had more than one pivot size. One recent watch I worked on, for example, had staffs available in pivot sizes ranging from .10 to .12 in diameter. As a result, the balance hole jewels could also vary in size.
You see where this is going. The pivot size of your new balance staff should be the same as your old staff. If not, it will either be too big (preventing it from fitting through the balance jewel hole) or too small (causing too much sideshake and hence poor timing) for your jewels.
You can measure the pivot size of the old balance staff or measure the hole size of your jewels. It’s usually easier to measure the staff, unless you happen to have a set of hole feeler gauges.
Most jeweling sets have a pivot gauge. Assuming your broken balance staff has a good pivot, you can measure it on the pivot gauge, like so.
If both pivots are broken, you can measure the pivots of the new staff in reference to your current balance hole jewels.
For example, here’s the new staff I used for our Illinois Santa Fe Special.
I tested the staff by placing the jewels on it, and the fit was good. Notice that the pivot pokes out but doesn’t have much room to wiggle laterally.
If you put the staff in the watch instead of removing the balance jewel, the staff should tilt around 5 degrees, according to Fried.
It is wise, on older watches, to measure both the upper and lower jewels. In olden times, a watchmaker might correct for a worn pivot by swapping a jewel with a smaller hole, so the upper and lower jewel holes might differ in size.
After measuring the pivot sizes, you’ll want to measure a couple more aspects of the new staff.
First, check that the hole in the balance wheel fits snugly over the balance shoulder of the new staff. The wheel should sit firmly on the new staff’s balance seat. If the hole is too big, you won’t be able to stake the wheel and staff together. In the picture below, the wheel fits nicely over the balance shoulder.
Finally, measure the roller hole on the staff. The roller should easily slide 50% down the roller post, the thick portion of the lower staff. Fried, in The Watch Repairer’s Manual, offers this rule of thumb: “A well-fitting staff will permit the roller table to be pushed down with the tweezers about three-quarters of the roller post before being staked down to the roller hub.”
In the picture below, the fit is pretty good.
But in this picture, the hole is far too small.
If the roller table’s hole is too small, the table will crack when staked. And if it is too big, it won’t fit tightly.
In Part 2, we’ll learn how to disassemble the balance by removing the hairspring and roller, so prepare the staking set and a pot of coffee.