Busted staff in Cyma 570--attempting to turn a new one

[LittleWatchShop]

I have been able to modify a staff twice in the past.  Made several attempts to turn from scratch, but I don't think I completed one.

Trying again.

The DeCarle book on machinist describes two ways to turn a staff.  One without removing the stock--cut the entire staff in one swell foop.  The other is to turn half of the staff and turn it to finish the other half.

Question 1:  Which is the better way--recognizing that I am a beginner?

If the answer is to do half, flip, do the other half, there is another question.

Question 2: Should I turn the HS collet side first BECAUSE it has a fixed diameter and thus easier to lock in to the lathe collet when turned?  The roller table side is tapered.

(unfortunately, I left the DeCarle book at my house in another city, so I cannot see what he recommends)

I am using what I think is blue pivot steel and I am turning with a Waller carbide graver.  Frankly the graver the pivot steel like butter making me think this steel is too soft.

Assuming I am able to create the proper staff provile...

Question 3: Should I heat it up and quench it in oil to harden it?  It is awfully presumptive to ask this last question...thinking maybe I will get this far...

I think I have found (and ordered) a balance complete but am determined to see this through.  Yesterday I was so crestfallen over busting the staff...just ruined my day, so I am seeking redemption through this effort.

Tag @nickelsilver@jdm

 

[nickelsilver]

You can test if the steel is "blue hard"; if a file will bite it, but you can't cut it with a jeweler's saw it's proper blue.

 

If you have great collets, go ahead and flip it. Yes, do the upper side first as the balance diameter makes a good place to grip when you flip. When you flip, grip lightly in the collet, then checking at 10x or so turn the spindle by hand with the T rest up close to check for concentricity, nudge true as needed then tighten.

 

If your collets (or the size needed for the flip) aren't that hot, best to do it in one go. Much harder to accurately measure the stuff collet side of the staff hub unless you have the right gear, haha.

 

If it's blue steel no need to heat treat. I cut mine from soft steel using slide rest, leaving what will become the pivots a good 0.2mm oversize and the roller table diameter cylindrical, heat treat, then finish the pivots, rivet, hub, and roller table diameter by hand, holding bottom half first to finish hairspring side, then as above.

 

Finish the pivots in a Jacot tool of course (leave them 0.01mm oversize for finishing)- but if you don't have one or know how to use it just concentrate on making a good staff. Crisp square shoulders, nice smooth cylinders, nice radius blending to the pivots. You only need about 0.01mm max interference for the roller fit- less if it's steel.

Edited April 20, 2022 by nickelsilver

[LittleWatchShop]

Well...may be all moot unless I can find the specs on the Cyma 570 staff.  I flung it and have not found it yet.

Balancestaffs.com gives me two dimensions only.

[LittleWatchShop]

9 minutes ago, LittleWatchShop said:

Well...may be all moot unless I can find the specs on the Cyma 570 staff.  I flung it and have not found it yet.

Balancestaffs.com gives me two dimensions only.

Found it...missed it on balancestaffs.com

[LittleWatchShop]

Hours on the lathe with only a modicum of progress. Progress is defined by a series of failures.

Where I am now is a partial modification of a staff from a box of pocket watch staffs that I have.  I have turned the roller table side and found that the dimensions above are a little small for my roller table.  I think I will use some medium tube-fitting loctite.  The HS collet side is now turned to have a snug fit.  The shoulder fits the balance wheel in a semi-snug fit. The staff is too long, so tomorrow, I will be turning the ends to meet the height requirement.

I see the same cutting performance on the stock staff as I do on my blue steel, so my steel is probably appropriate for the task (though I will not be using it).

Success or failure aside...I am getting better and turning and sharpening my gravers.

Meanwhile...I have a balance complete coming from the UK.

[LittleWatchShop]

Once I get a prototype staff, I would like to mount it to the balance wheel temporarily so that I can put it in the watch and check for end/side shake.  If I have to modify the staff, I could remove it.  Maybe this is not the way to do it.  I have stepped collets that, I suppose, I could mount the balance/staff and turn the staff down (shorter) while still mounted on the balance rim.

Thoughts?