Two parts or a split roller-table ??

[Endeavor]

I disassembled a balance assembly of a 1930's CYMA 797 in order to replace the broken balance staff.

I carefully removed the roller table and the safety roller, which I thought were both one solid piece. The roller-table was pushed off the balance-staff from in between the roller-seat and the roller-table, so the safety roller hasn't seen any force, apart from compression.

To my surprise they were separate, a roller table and a safety roller.

There are two indents in the roller-table, but not much to see on the bottom edge of the safety roller.

Did they become separated or are they separate by design ??

Do I have the same as Mark has in his video "Fitting a new balance staff to a vintage 1940s CYMA"?  Coincidentally also a CYMA movement with the same shape roller-table & safety roller, also from the '30's / 40's.

Starting from the 3:30min mark;

 

Is this the "joy of watch repair", as Mark remarks at 15:15min when assembling the roller??

 

Edited February 26, 2023 by Endeavor

[nickelsilver]

2 piece rollers do exist, roller table and safety roller, and I think Mark is mistaken that his has split; from your photos the grained surface on the main piece is uniform up to the hole, with no sign of breakage (and the hole in the safety roller is chamfered on both ends).

 

More commonly with two piece rollers the two pieces fit on distinctly different diameters, and the safety roller doesn't have the tube section. Very tricky to get the fit just right on those.

[Endeavor]

I just can't believe my luck !!

First time ever to change out a balance staff and meet nearly all the complications there are!

When assembling, how does one line the roller-table and the safety roller up, eyeballing or is there a more sophisticated method?

[nickelsilver]

6 minutes ago, Endeavor said:

I just can't believe my luck !!

First time ever to change out a balance staff and meet nearly all the complications there are!

When assembling, how does one line the roller-table and the safety roller up, eyeballing or is there a more sophisticated method?

Eyeballing is fine- eyes are pretty good at lining things up!

[Endeavor]

So the roller table is friction-held in place by the bottom edge of the safety-roller?

I carefully replaced the roller-table and it doesn't fully bottom out on the roller-seat, so maybe the roller-table is also held in place by friction on the staff? I didn't try to push it any further, didn't want to enlarge the hole unnecessarily.

Anyhow, I'm already happy that it wasn't me, but it was by design .....

 

Edited February 26, 2023 by Endeavor

[nickelsilver]

With a steel roller, you want it to go almost to the hub, maybe 1/2 to 1 (max) thickness of the roller away, before pressing all the way. The safety roller similar. If it seats too far from the hub initially there's a big risk of bending or breaking something. With your two piece roller both parts need to be a friction fit.

 

Same really goes for a one piece roller, you want it to seat about one thickness of the roller- the part with the roller jewel- from the hub. They are most often brass or similar, and can crush easily if they seat too far away and then get forced down.

Edited February 26, 2023 by nickelsilver

[Endeavor]

The roller, gently pushed, sits indeed about between 1/2 to 1 of its thickness above the staff's roller-seat. So, I guess, that will be fine ...... that is, when the new staff is 100% identical in dimensions ...... for that we have to wait until the new balance staff's arrive. The Danish PostNord is very, very slow .... from the moment CousinsUK ships it, at least 3 weeks, perhaps 4 weeks !

Thanks for your help so far ! ......

 

Edited February 26, 2023 by Endeavor

[rehajm]

9 hours ago, nickelsilver said:

 

2 piece rollers do exist, roller table and safety roller, and I think Mark is mistaken that his has split; from your photos the grained surface on the main piece is uniform up to the hole, with no sign of breakage (and the hole in the safety roller is chamfered on both ends).

 

More commonly with two piece rollers the two pieces fit on distinctly different diameters, and the safety roller doesn't have the tube section. Very tricky to get the fit just right on those.

 

Yes, much to my surprise when I removed the roller on a Waltham- I thought I had broken it as well…

Edited February 26, 2023 by rehajm

[Endeavor]

@Mark thought this may be some of your interest

 

[Mark]

Yes. It is a two part, I’ve seen exactly the same since although the roller (not plate with impulse) did seem to be spread out on that watch - I did that video 9 years ago and have not looked at it since until today  

[thor447]

I just ran into this tonight while doing a balance staff replacement on an Elgin 478.  It surprised me for sure, and I initially thought I had broken something.  On closer inspection it didn't appear that I had, and thankfully I found this thread afterwards.  Thanks to all.  My blood pressure is coming back down now!

[JohnR725]

1 hour ago, thor447 said:

Elgin 478.  It surprised me for sure, and I initially thought I had broken something.  On closer inspection it didn't appear that I had, and thankfully I found this thread afterwards. 

Here's something that Elgin had on the subject.

Then we have Waltham Where sometimes it's a little confusing over what exactly your disassembling. Fortunately friction staff's typically have a blued steel hub.