...it's been my, albeit limited, experience that in the process of restaffing a watch that the 'fit' at the table(s) and h'spring collet tends to be somewhat loose on the replacement staff despite taking due care w/their removal from the broken staff...is this usual and what is the remedy?...thanks....Jim C

Jim,

Are you using genuine replacement staffs? Before installing a new staff, it is important to measure the hairspring, balance arm and roller seats, the overall length (add approx .2 - .3 mm for each missing pivot), shoulder width and pivot size of the old and new staff. The staff you removed may not have been cut to factory specs. It's important to know what the correct specs are for any staff replacement.

If you can provide me with the staff part number, I will look in my staff book and provide you with the dimensions of what an original staff should be. Someone could have installed a staff that was a little too large in the dimensions you described and then opened the HS collet and roller table.

I could be incorrect on the missing pivot lengths for 16s to 18s. If so, I will correct them later. I'm at work with no data available.

If no major adjustments are required, you can close the hole slightly in the roller table and/or HS collet for a tighter fit. Caution must be exercised not to crack the HS collet or roller table.

John D. Duvall
Vice President, Education

...JD...the spec's on the original staff on the Ham 974 that I was referring to are: pivot 0.11mm; overall length 5.30mm (overall estimate since one pivot was broken); roller seat 0.70mm; collet seat 0.77; balance seat 1.26mm...and the measured specs on the #435(old) replacement closely match these specs...thanks...Jim C

Jim,

My staff book indicates two styles of #435, single roller staffs. Both styles have the following dimensions:

Total length: 5.30
Balance seat: 1.28
Roller seat: .71
Hub thickness: .58

The only difference between the two styles is the HS collet seat:

Large Collet seat (LC): .97
Small Collet seat (SC): .77

If the old staff and your new staff have the same dimensions, the HS collet must have been stretched open slightly or cracked during removal or it was loose in the beginning.

I've experienced (limited) .01 to .03 differences in the seat sizes between staffs from different makers that will probably affect the roller table and balance arm more than the HS collet.

Hope the above dimensions help you figure out your problem!

John D. Duvall
Vice President, Education

...thanks JD...I think I'll invest in a collet closing tool...w/regard to the roller table (and
I've always opposed this closing adjustment with clock pivot holes), I'm wondering if I can't use one of the staking punches which seemed shaped for such a purpose to slightly close the hole in the roller table...thanks again...Jim C

Jim,

I've used a round nosed punch to close roller tables. Be careful that it clears the roller jewel and that it is centered over the hole (single roller). There's always the possibility of the hole becoming off centered which can lead to other problems, so be careful and start with "light" taps, check for fit and repeat as necessary.

I've done this only once but I closed a HS collet using a lathe collet. Do a fit check to see if the HS collet has enough grip area for the lathe collet. Be extremely careful and tighten the draw handle only enough to close the lathe collet a small amount. Remove and check for fit. If necessary, repeat. First, practice this procedure on a bad HS that is no longer fit for use.

John D. Duvall
Vice President, Education

...thanks JD...Jim C