1915 Hamilton Grade 974 Model 2 16s balance staff repair

[MechanicMike]

Hi all

doing my very first full repair on a balance staff/wheel assy. which includes removing the broken staff to replace it, roller table to re-shellack the impulse pin, clean, poise, truing, etc etc. After i removed the bad staff I noticed in the balance arm bore looks kinda ragged. my questions are: do I take a jeweling reamer or broach to remove those or proceed with staking the new staff in and prepare for riveting? 

2nd question: looks like the old pivot measures .12mm and the new one is .13mm will i need to remove that extra .1mm? i'm thinking I do but all I have is a Levin pivot polisher, a few ruby and steel burnishers. I have no lathe. pic #1 shows the burrs.

[Nucejoe]

 You might try to put the staff on the mainplate and tighten the cock screws to find the answer yourself, I think there be no need to shorten the staff, not for  .01 mm anyway. You would lose the original fine polish and gain nothing instead.

 

 

[JohnR725]

18 hours ago, MechanicMike said:

my questions are: do I take a jeweling reamer or broach to remove those or proceed with staking the new staff in and prepare for riveting?

It's really hard to tell in your picture how bad that really is try a toothpick something soft do not use anything metal on the hole.

Out of curiosity how did you remove the old staff?

18 hours ago, MechanicMike said:

2nd question: looks like the old pivot measures .12mm and the new one is .13mm will i need to remove that extra .1mm? i'm thinking I do but all I have is a Levin pivot polisher, a few ruby and steel burnishers. I have no lathe. pic #1 shows the burrs.

What you should do is try the new staff in the jewel to see how it fits. There is no guarantee that the old staff was the right size if somebody had already restaffed the watch. Then I'm attaching an image that kinda gives you a clue if you put a new staff in it should have so much lean. Then you have to check both jewels because sometimes they end up being different sizes somebody might have changed one and didn't put the right size back in.

Also it's important to measure all of the dimensions on the old staff and compared to the new staff just to make sure that everything else is the right size to avoid unpleasant surprises.

 

[MechanicMike]

23 hours ago, Nucejoe said:

 You might try to put the staff on the mainplate and tighten the cock screws to find the answer yourself, I think there be no need to shorten the staff, not for  .01 mm anyway. You would lose the original fine polish and gain nothing instead.

 

 

thanks Joe I never thought of that! 

5 hours ago, JohnR725 said:

Out of curiosity how did you remove the old staff?

ah sharp eye you've got there John. I was waiting for this question lol...I don't have a lathe to undercut the rivet before staking it out so I used my staff remover tool. it came out nice and easy but did I make those burrs? sure possibly. I tried to get better pics but can only do so much with my phone. sorry. the burrs aren't terribly bad but the machinist in me wants to remove them. I'll try the non metallic trick you mentioned. examine the pics again and compare pic #1 to pic #2. that's about the only way i could get some sort of contrast on the burrs. I'll see if I can try something else.

I had tried the new staff in the jewels and they fit but because this ones my first I have nothing to compare the "feel" to in checking for end/side shake. the old staff upper pivot was completely gone and the lower was bent but was able to obtain somewhat of a diameter off it. I'm going to go back and do what Joe described above to check for fit, endplay etc. etc. check jewels re-measure.

6 hours ago, JohnR725 said:

a toothpick something soft

got just the thing-a tiny plastic toothpick. I'll try pegging it with that. and a wooden one of course.

[MechanicMike]

all done! thanks for the help guys. John I went ahead and gave the pegging thing a try but no luck. so heres what I did: First of all, under closer magnification I found out they weren't burrs, but stake marks. 3 of them spaced around the diameter. Have you ever seen that before? staking the bore on a balance wheel?

I have a jeweler's countersink in my staking kit that, along with a jewel reamer I gently teased the stake marks from the bore. riveted the new staff in and it worked great. again, thanks.