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Hardening and tempering a balance staff


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Couple of questions about hardening and tempering a balance staff.

First, I've seen some conflicting advice about turning the staff in the hard vs soft state. My references say to harden and temper the stock and then turn, but I think it was @nickelsilver who said he turns the staff in the soft state, then hardens and tempers.  What is the advantage?

Second, what about flux when hardening? Is it worth bothering with on a small part like a staff? When I harden a piece of stock and use boric acid or Borax slurry as flux, it leaves a coating on the stock that's a pain to remove so that I can then temper to blue.  I could see this being problematic when hardening a turned staff,  removing the residue from pivots could end in tears 🙂

Anyway,  it would be great to hear any thoughts about this. 

Cheers!

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I make lots of turned parts from steel, from staffs and stems to pinions and barrel arbors and so forth. I do it all with the steel in its annealed state, then harden and temper. There is a risk of things warping in heat treat, but from experience it rarely happens. Also, regarding stems, threading hardened and tempered steel is a quick way to ruin an expensive (and hard to get now) die. All commercially made watch components are made from steel in the annealed state, then hardened and tempered.

 

When making a staff I will blank it out using the slide rest, leaving the pivots unfinished (turned to length, but just slightly smaller in diameter than the next diameter), the rivet uncut, the back taper on the hub uncut, and the taper for the roller table uncut i.e. oversize- all the other diameters to size. After heat treat, chuck on the hub or roller diameter, finish the pivot freehand leaving 0.01mm for the Jacot, cut the rivet, finish the various diameters. Flip around and hold by the balance diameter, cut lower pivot, cut taper for roller table, and back taper on the hub,  do finishing work. Stake to balance, finish pivot diameters in the Jacot, and finally finish the pivot ends in the lathe- I just find it faster and easier than using the lanterns on the Jacot. Done.

 

For heat treating I also find using borax/boric acid (not exactly the same thing, but same function) or soap or even fancy stuff like Brownells anti-scale all tend to be somewhere between a pain in the rear to almost useless. I learned many years ago to use wood charcoal finely ground, in a tube, with the part down in there. Heat to bright orange and dump the whole lot into oil. I use old nitrous oxide or CO2 cartridges that have been cut open as the tube (welded to a rod). It's a little messy, and I keep a commercial espresso grinder just for grinding the charcoal, but the parts come out a clean grey and can go straight to tempering without further clean up aside from removing the oil. You can get finely ground charcoal powder from health food stores if you want to try and don't have a spare espresso grinder around, haha. The tube helps distribute the heat, which is a big help. No binding wire, no cleaning off borax, no burned in pits.

 

Hardening

IMG_0010 (Large).JPG

 

Balance staff blanked out

balance staf blank.jpg

Edited by nickelsilver
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I have resorted to making staffs by starting with a larger staff.  For example, starting with a pocket watch staff that has all critical dimensions greater than I need.  Then I turn it down to size.

What I have noticed is that it is relatively easy to make the cuts with a carbide graver.  I have worked with blue steel raw stock that is harder to cut.  This is a mystery to me because these staffs that I start with are intended to go directly into a watch as a replacement.  I do keep my carbide gravers sharp...so maybe the steel is harder than I think.

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Since I'm starting to turn soon, the above is helpful, but does sound a little messy.  Does anyone use the technique that Tanaka uses at time index 40:28?  It appears he wraps the part in wire, drags it in some soap, indirectly heats, and drops into water.  He still has to scrape it with a fiberglass brush, but it doesn't look like too much work.

 

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7 hours ago, nickelsilver said:

When making a staff I will blank it out using the slide rest, leaving the pivots unfinished (turned to length, but just slightly smaller in diameter than the next diameter), the rivet uncut, the back taper on the hub uncut, and the taper for the roller table uncut i.e. oversize- all the other diameters to size. After heat treat, chuck on the hub or roller diameter, finish the pivot freehand leaving 0.01mm for the Jacot, cut the rivet, finish the various diameters. Flip around and hold by the balance diameter, cut lower pivot, cut taper for roller table, and back taper on the hub,  do finishing work. Stake to balance, finish pivot diameters in the Jacot, and finally finish the pivot ends in the lathe- I just find it faster and easier than using the lanterns on the Jacot. Done.

 

For heat treating I also find using borax/boric acid (not exactly the same thing, but same function) or soap or even fancy stuff like Brownells anti-scale all tend to be somewhere between a pain in the rear to almost useless. I learned many years ago to use wood charcoal finely ground, in a tube, with the part down in there. Heat to bright orange and dump the whole lot into oil. I use old nitrous oxide or CO2 cartridges that have been cut open as the tube (welded to a rod). It's a little messy, and I keep a commercial espresso grinder just for grinding the charcoal, but the parts come out a clean grey and can go straight to tempering without further clean up aside from removing the oil. You can get finely ground charcoal powder from health food stores if you want to try and don't have a spare espresso grinder around, haha. The tube helps distribute the heat, which is a big help. No binding wire, no cleaning off borax, no burned in pits.

 

Thanks for this, the procedure makes perfect sense to me. Rough cut in the annealed state, finish after hardening and tempering.  The only thing that might trip me up is the hub taper. Reason being is that i'm using a Sherline, and I don't have a compound cross-slide. I use cemented carbide tools, and all my angles are done with the side of the tool. That might be tricky on a hardened hub when holding on the collet or roller shoulder.  Also, why not cut the rivet when it's soft? I just busted the tip of my last E4 tool trying to cut the rivet on a hardened blank 🙂

I like your heat treat setup, but I don't have the space to do anything quite so robust. You technique reminded me, though, of something that was suggested by Jerry Keiffer. He uses steel tubing that he packs with the part and some paper, which he then seals by whacking ball bearings into the ends of the tube.  The idea of the paper is to flash off any oxygen in the tube, which he says prevents scale formation. I think this is something that I can try, steel tubing and a small tubing cutter should be cheap enough. I think for an experiment crimping the ends of the tubing might work well enough, as long as I don't smash the part. 🙂   I can try the charcoal too, as it seems to me that it would be better for heat transfer, but I see a big mess in my future. I've got a mortar and pestle so I can make some powder. 

One last question, I'm using O-1 tool steel.  What hardness should I be shooting for with a staff? I'm used to seeing a Rockwell C hardness in the mid 50's as a sweet sport for toughness, and that would suggest a tempering temperature of about 600F/316C which I believe would be an oxidation color of pale to grey blue.  Does that seem right?

Thanks again for your considered reply and, 

Cheers!

6 hours ago, pent said:

Since I'm starting to turn soon, the above is helpful, but does sound a little messy.  Does anyone use the technique that Tanaka uses at time index 40:28?  It appears he wraps the part in wire, drags it in some soap, indirectly heats, and drops into water.  He still has to scrape it with a fiberglass brush, but it doesn't look like too much work.

I remember seeing that video, and it is similar to what I've been doing. I just use boric acid or Borax slurry for flux, and mineral oil for quenching.  I think I will try soap, just to see what happens. The boric acid/Borax leaves a glassy coating which is a pain to clean up on a small part.  

6 hours ago, LittleWatchShop said:

I have resorted to making staffs by starting with a larger staff.  For example, starting with a pocket watch staff that has all critical dimensions greater than I need.  Then I turn it down to size.

What I have noticed is that it is relatively easy to make the cuts with a carbide graver.  I have worked with blue steel raw stock that is harder to cut.  This is a mystery to me because these staffs that I start with are intended to go directly into a watch as a replacement.  I do keep my carbide gravers sharp...so maybe the steel is harder than I think.

Unfortunately, I'm doing this staff because the collet shoulder is bigger than on the ones that I can buy. Old Waltham pocket watch. 

And as far as the stock is concerned, "blue steel"  could be just about anything, and unless the supplier gives you specs who knows how hard it is when you get it. If it is too hard to work with, you could try annealing it, and then see how easy it is to cut.  Quick and dirty just heat to bright orange like @nickelsilver said, but cool it very slowly, don't quench.

This DIY heat treating is new to me, I know about tool steel heat treating as this was a big part of our process at Speco, but we always used sub contractors. Stopped doing in house heat treat around the time that I started there. It can get very complex, depending on what you are trying to accomplish,  but I think for our purposes KISS applies.

Getting even heating, avoiding fire scale, and learning the oxidation color/temperature relationship seem to be the most important things that I need to do.  That and not making a mess or burning down the townhouse 🙂

Cheers!

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13 hours ago, Klassiker said:

Do you do this yourself from a standardised stock, or do you have a consistent source?

From Frank's post I understand he heat treats his own steel prior to turning. I used to do that too. In school they do have you do a lot of hand turning from "blue" steel; but I find the rods available to be of questionable quality, both old stock Bergeon* and other that I have found and tried. Doing it yourself gives better results.

 

*I had some old Bergeon steel that was so strange, like inconsistently hardened, that it would only turn ovals.

 

One of my old students makes his living making components for other watchmakers, and he went back and forth and finally settled on pre heat treated steel he makes, and makes the staffs directly from that. He might have to touch up the lathe tool/s a time or two during the process, but he still takes about the same amount of time for a staff that I do. I often do batches of components, so being able to rely on a tool to make it through the batch is more important to me. Plus, I won't cut threads on blue steel (stems), or cut teeth (pinions), so everything gets a post-heat treat.

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1 hour ago, praezis said:

blue steel“.

a very long time ago I had purchased an assortment of blued steel and yes it's a nice dark blue. Then I had the weird feeling that maybe it had been colored rather than actually blued? Plus a lot of the pieces of and I will use the term steel loosely year seemed to be distorted and well just not quite straight. Or basically worthless.

Little while back is watching on YouTube somebody visiting a factory in Switzerland that makes CNC machinery for use in watchmaking and they also visited a factory that was using all the machines to make watch parts somewhere in the video beat or videos I did see a cut balance staff. So I wondered with the machines like this whether they're cutting it from the steel of the right hardness or whether they have to go often be hardened? Then the sad aspect was the wire for the machine was in very long pieces. I'm guessing like 10 feet long I believe in the second video when he was looking at the raw stock there was a reference to moving it was an issue because you bend it because it is an long pieces. In other words very impractical for us to buy unfortunately.

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28 minutes ago, JohnR725 said:

Little while back is watching on YouTube somebody visiting a factory in Switzerland that makes CNC machinery for use in watchmaking and they also visited a factory that was using all the machines to make watch parts somewhere in the video beat or videos I did see a cut balance staff.

I can't find the video where balance staffs are cut, but this video shows some of the bar stock used (at 1 min) 

 

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3 meters is a standard bar length for automatic lathes. My main supplier will sell as little as a meter though, or cut a 3m bar into meter lengths or whatever. The longtime standard steel for watch parts is Sandvik 20AP, but that is getting phased out for alternatives that don't include lead (leaded steel is a mainstay for automatic lathe work due to vastly increased tool life). The above supplier Klein, developed their own alloy LAW 100X with Carpenter Steel, which is lead-free, and I find cuts just as well as 20AP and is very stable in heat treat. Otherwise back before I moved to Switzerland, I used good-old O1 tool steel for everything with no issues. Cheap and predictable. Man, I needed some larger diameter for a project earlier this year, and Klein wanted like 600 bucks for 1m of 25mm diameter! Found a European supplier of O1 and got a meter for 70 bucks. And I still have 970mm of it 😅.

Edited by nickelsilver
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The Sandvik 20AP sounds similar to the 12L14 alloy that's often recommended for easy machining. McMaster has 1215 which they say is a lead free equivalent.  LAW 100X is very interesting, it is the same alloy as AISI 1095, but is powder melted steel, which Klein says results in a fine structure, important for small parts.  It looks like it's available in the states, but whenever I see a supplier that has "contact for a quote" as the price, I *know* it's going to be expensive 🙂

Eventually I may try some other steels, I might get some 12L14 or some S7, but for now I'm going to stick with the O1 and try and get my machining and hardening techniques dialed in.

 

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Nonono 😄, 20AP is miles different than 12L14. That stuff machines almost like brass, and isn't heat treatable. I would say 20AP is a little easier to machine than O1. For an automatic lathe that little bit, over 5k parts makes a difference.

 

It's funny that Law 100x falls under the 1095 désignation, goes to show the little details count. O1 is a wonderful steel, as you're stateside easy as pie to get but I recommend getting "nice" stuff, i.e. if looking at MSC or McMaster stick with the slightly more expensive non-import stuff. Details.

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Whoops, yes, although a carbon steel, you can only case harden 12L14.  I still can't figure out the standard designation for 20AP, perhaps there isn't one. Not one I'm familiar with.

And yes, for rod stock McMaster-Carr is the bees knees.  Good prices and fast delivery. 

Thanks!

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6 hours ago, mikepilk said:

I can't find the video where balance staffs are cut, but this video shows some of the bar stock used (at 1 min) 

I think it sends the higher video where he goes to the factory they make the machines where you see a balance staff is one of the things they made. Then in one of his newest videos he showed how to make really tiny screws with the machine unfortunately I don't think he ever said what one of these things costs.

 

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  • 2 weeks later...

Aargh.  I am having a heck of a time cutting hardened and tempered O-1.  No trouble in the annealed state, but once it's hard I'm just pushing up giant burrs and not actually cutting much. Small diameters are just bouncing around and the tool is not biting. Or if it is, it's a jerky cut then skip thing that's not ending well.

@nickelsilver, what annealing temperature/color should I be going for?  And @praezis, did you ever find the specs on the steel you are using?

I'm trying to figure out if I have a tooling problem or a material problem, and I'm not making much progress.

I've heat treated a few test pieces that are pictured, but so far the different tempers don't seem to be making much difference. 

 

IMG_20230903_144508_cr.jpg

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