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Hardening and tempering a balance staff


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I temper to blue like the second from the left in your pic. If you are cutting it in that state, with the slide rest (I know you are using a Sherline), the tool has to be really sharp, and will need touching up frequently. The moment it gets the slightest bit dull, and there is any resistance to cutting, you work harden the surface further, causing the tool to dull further, and it's over. Cutting hardened and tempered steel is much easier with a handheld graver. For the tapers on the hub and roller diameter, trying to do it with full contact of an angled cutting tool is going to be next to impossible, especially for the roller diameter. With a regular watchmaker lathe it's no problem to angle the slide, but I know that's not an option on the Sherline. Even though I have a "normal" watchmaker lathe with a killer slide, I still cut these features by hand because it's just faster and and equally important- easier.

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3 hours ago, JohnR725 said:

What sort of cutting tool are you using?

Brazed micrograin carbide, Micro-100 D-4 which is an 80 degree neutral tip.

3 hours ago, praezis said:

Hi,

already mentioned it somewhere, I use „silver steel“. Not to recommend for hardening after cutting, as it distorts then (however not using N‘s method).

Frank

This stuff?  

Silver Steel - (1.2210)
Silver steel round bars without machining allowance - bar length 1000 mm

Silver steel (1.2210)  slightly alloyed high carbon steel. 1.2210 (115CrV3) is a cold work steel used for a wide range of applications. It has good machinability, offering high hardness and wear resistance it is widely used in general engineering. The name silver steel came about because of the silver appearance due to the addition of chromium which adds to the strength and hardness of silver steel.

Typical chemical composition of Silver steel (1.2210)
C    Si    Mn    P    S    Cr    V
1.10-1.25%    0.15-0.30%    0.20-0.40%    0-0.03%    0-0.03%    0.50-0.80%    0.07-0.12%
 

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3 hours ago, oldhippy said:

I used tungsten carbide gravers.

I'm assuming the handheld carbide gravers?

4 hours ago, dadistic said:

Brazed micrograin carbide, Micro-100 D-4 which is an 80 degree neutral tip.

Can we have a picture of how your holding the cutter in the lathe?

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4 hours ago, praezis said:

yes. 

Probably I would try O1 if available in Germany with small diameters.

Btw. Did you try cutting with HSS?

Frank

HSS on hardened tool steel?  No, I wouldn't have expected that to work.  I could try it, but I'm not sure if my HSS tools are in good shape.  In the distant past I have made my own HSS tools from blanks, but right now I don't have a way to grind them. 

53 minutes ago, JohnR725 said:

Can we have a picture of how your holding the cutter in the lathe?

Sure, this one is in a standard tool posts with some shims to bring the nose down to the centerline. It turns out by that moving the stock down the cutting edge of the tool to a part that hasn't been used much I can make chips, so the tool has failed. Tool wear towards the nose also explains why the edge of the tool didn't look like it was straight.  

IMG_20230904_093936.jpg

DSC_1695.JPG

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Honing the top of the tool has improved cutting. The edge closer to the nose is cutting again, and the surface finish is better. If I could hold the tool well enough to hone the sides, I think it would be even better. However, holding everything by hand makes it too difficult to do the side. I need a better way if I'm going to do more of this, my fingers are sore 🙂

 

DSC_1701.JPG

Edited by dadistic
grammar
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Great thread, great info here, thank you all.

It’s looking like I’m going to be turning the pivots on a new balance staff here real soon and am wondering if I should anneal the staff first. 
I have an old Sureline 1000 lathe and can grind my carbide cutter to shape and sharpen them.  
I’ve never machined pivots before, and can imagine snapping them off pretty quickly.  

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Well, I think most folks who use a watchmakers lathe machine the pivots in the tempered (blue)  state.  This is what has been giving me problems, but I have actually done pivots that looked almost like a pivot should 🙂 I need more practice to hold size, though. 

Based on a suggestion from Jerry Keiffer, I used an AL-4 brazed carbide tool to form the pivot. The tool nose radius is just about right for turning the pivot. 

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  • 2 months later...

Interesting thread. A little cold, but I came to it just last night.

If interesting, I can share my experience, which is generally turning pre-hardened and tempered to blue steel in a big lathe wit cross-slide support, using carbide cutters. In the distant past I have used T-rest and hand-held cutters too, and still use this technic when needed, but not often.

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OK,

I usually make balance staffs for big pocket watches out of rollers from roller bearings. This are rollers from car driveshafts bearings. I know people with car services and thus have unlimited source for material. The rollers are size 1.8-2.4mm diam.  X 10-15mm,  usually made of good steel and are hardened, need only tempering to deep blue. Actually, the tempering slightly depends on the steel sort, and there is a rule by G. Daniels that says 0.1mm test pivot should bent to 30 degr. before it breaks.

I also check if the test pivot is normally strong, as in some cases it will break much easier than a normal pivot, and then this lot of rollers (or steel) is not good for staffs.

For wrist and small pocket movements, where the pivots are thinner than 11, I usually use 115CrV3, this steel is superior to everything else that I have ever test, but I have limited quantity, it is soft and needs hardening and tempering. Working with this steel is a pleasure.

I also have and use soft У10А, which is Russian analog to O1. Usually make of it screws, stems, etc. It needs very careful heating when hardening, as overheating is easy and it ruins the steel, developing big grains structure and parts break easy.

Here is my main lathe, as You see it is really big and actually nothing to do with watchmakers lathe, just regular general purpose 70 cm lathe. But, I am able to make staffs for the smallest wrist calibers on it. I also make threaded parts on it, directly from blue steel, but with milling attachment instead of cutter.

20231116_103509.thumb.jpg.7619aaf3655418e8a0d9e158fee588db.jpg

The interesting here is this set of cutters, which are accepted on the place of the tool post. They are pre adjusted in high and ready to use. Changing the cutter takes minimal time. The cutters are tungsten carbide and are made of CNC router bits, which are cheap and easy to source.

 

20231116_103752.thumb.jpg.a494b0c0b6d9982b29acf3df0c7127e4.jpg

 

I use this kind of diamond disks to sharpen cutters. The smaller disks are cut from a bigger one, the disks also easy to source, grit 600 or 800.

20231116_165548.thumb.jpg.31b07a7bc91547f0f75355c15a80be37.jpg

I sharpen the main cutter every time when start new staff turning. If the cutter needs re-sharpening during the turning, this usually means that the steel is to-hard. If it is possible to turn 2-3 staffs without re-sharpening, then the steel is softer than needed. I have developed technic for easy maintaining the sizes in high and making one staff usually takes me about 30 min.

Edited by nevenbekriev
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Thanks for showing how you do staffs on an engine lathe. 

I've had to set aside my work for a while, as we are moving, again! Third time in three years. 

When I get things set up again,  I will be back trying to make staffs on a Sherline lathe.   A little more practice and I will get there. 

Cheers!

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