Smiths Platform Refurbishment - part 1, Balance Staff

[Boz]

Thanks to the support of this forum and my local BHI branch what started out as a hobby has become my second love (after my wife in case she is reading lol). So I've decided to make a second career of horology and signed up for the BHI DLC last July. Due to circumstances I'm following the clock path way though I still enjoy watched greatly. This may I'm completing the BHI technical grade exams plus, some of the next level modules. 

I've really enjoyed the making aspect but one thing I've put off has been making balance staffs. For some reason I found it intimidating.

As a starting point I've acquired a broken ABEC platform. It appears to have had a knock or shock. One balance pivot has snapped off and one pallet jewel is displaced. The upper pallet fork oil hole is damaged as well. It's also very scratched and corroded. 

I started with the staff. I thought the approach on the SLBHI youtube video looked straightforward so I followed that method. The staff is a simple shape, no waists on the pivots.  

A good opportunity to put my home made balance table to use for support whilst removing the hairspring.

Using 2mm pivot steel and initially using a 2.5mm carbide graver, I turned the post matching the length of each section by eye against the original, using a vernier caliper to check the diameters/taper followed by hand fitting to the wheel, collet and roller table once close. I turned the wheel side first and most of the roller table side but my graver was too large to finish it without turning the piece around. so I turned it and centred in the collet against my thumbnail. I left the pivots at 0.3mm as I intended to fit the wheel and complete them in the Jacot tool. Here is is, partly finished.

 

Using the Jacot tool I filed the pivots down to 0.11 mm then burnished them to 0.10 and polished the ends

 

 A test fitting revealed that the fit was generally good but the roller table was fractionally too low and the seat for the wheel needed cutting square so that it would fit flush. What I found particularly difficult was creating a perfectly square shoulder for the roller and wheel to sit against, as the carbide graver has a slight radius at the end. You can see that the wheel is not perfectly flush with the shoulder and the slight radius on the shoulder for the balance table: 

I switched to a 2mm lozenge shaped graver as the tip is finer so I could eliminate most of the radius in the shoulder, and used a ruby burnisher to remove the machining marks:

Adjustment made it fits well and runs freely. I always ask myself not only is this good enough, but also how could it be better. Whilst it is functionally fine, I think the finish could be better. It lacks crispness. I'm still pleased to have succeeded in making something that at least works. I'd love some feedback on how to do this better.

 Everything is sitting at the correct height:

I also broached out the damaged pivot hole for the pallet fork, and fitted a brass chaton and jewel. I thought the brass chaton looked wrong against the nickel plated bridge, and the bridge was terribly scratched and corroded, so I grained it and re-plated it. Please ignore the blue screws: I will bring the finish back to match the originals. I regret graining the bridge as I will not be able to get the plate to match it without pressing out the posts on which the cock and bridge are mounted.

 

Next task is to fix the displaced exit pallet jewel. I've done this before and it seemed straightforward. I'm not sure how to deal with the corrosion on the escapement wheel. I could make a plate with a tiny hole in it and rotate the top face of the wheel against some lapping film perhaps?

 

Edited April 22, 2023 by Boz
Typing errors