Pocket Watch Balance Staff (graver turning, by hand)

[mars-red]

In one of my other posts I threatened to post some pics of some of the really small stuff I attempt. This evening I made what I think (unless I lost count, which is possible) is my sixth attempt at turning a balance staff for an antique French pocket watch.

I thought some of you might get a kick out of it, not only due to the small size, but the fact that the turning is done using a hand-held graver against a "T" rest (sort of like wood turning lathes). These days I sort of cheat by roughing them in with the cross slide, then finishing up with hand held gravers... that saves a lot of time. I tend to use either O1 or W1 drill rod, and hardening and tempering must be done prior to turning the part. The temper is a bright blue, so sharp high speed steel still cuts it with ease. If you've never tried turning spring-tempered O1 or W1 with sharp high speed steel, I recommend trying it sometime... it machines beautifully and leaves a really nice finish.

This pic shows the completed staff, before parting off. The diameter of the pivots is less than 0.005", so you can imagine how nerve-wracking it is when you get to the one closest to the collet. I started out using tailstock support with a safety center, to keep the staff from wobbling during those final cuts, but I've since got the hang of a really delicate touch so I no longer need to support the part at all.


Here it is again, after parting off:


The portion of the staff where the roller table and safety roller will be seated do not demand perfect concentricity, so for turning that section to the final diameter (which also has a slight taper), one has the option of either reversing the part in a collet (and suffering the resulting concentricity error), using a "cement" or "wax" chuck (which I have had no luck with at all), or turning between centers using special safety centers to avoid damaging the delicate pivots. Once that is dealt with, the staff will be set up in a Jacot tool (a tiny, specialized dead center lathe) to burnish the pivots to their final diameter (about 0.0045" in this case).

I have come close to success in some of my previous attempts. My last attempt, for example, went quite well until I discovered there was an error in the overall height of the staff. I went back to the drawing board and spent a few more hours taking measurements to find the source of my error. This has certainly been great practice!

[redneckalbertan]

I thought some of you might get a kick out of it, not only due to the small size, but the fact that the turning is done using a hand-held graver against a "T" rest (sort of like wood turning lathes). These days I sort of cheat by roughing them in with the cross slide, then finishing up with hand held gravers... that saves a lot of time.

Wow... Beautiful work.

I do have a couple question for you if you don't mind. Please forgive me if they seem trivial.

Why do you use hand held tools for this small work?

Wouldn't using a tool holder on the cross slide be more accurate and precise?

I am blown away by the beauty of this little piece.

[wsippola]

Very nice work! I've made a few, it usually takes at least two attempts for me to be successful. I cheat and flip it end for end to do the bottom half, just using the collet. Probably shows on the balance wheel, but it's been a while since the last one. I would get the pivots close to size and then use a ruby slip and fit to the jewels. Again, very nice work,

Wayne

[mars-red]

Wow... Beautiful work.

I do have a couple question for you if you don't mind. Please forgive me if they seem trivial.

Why do you use hand held tools for this small work?

Wouldn't using a tool holder on the cross slide be more accurate and precise?

I am blown away by the beauty of this little piece.

Thanks very much for the compliments!

The human machine is capable of extraordinary accuracy. With the amount of practice true watchmakers put into hand turning technique, the precision and level of control is unrivaled (except by perhaps the most exotic of automated equipment). And it is really the level of control where trying to do this on a machine slide would fall short. I think you can further break down the aspect of control into two parts: feedback, and versatility (or adaptability). You simply will not get better feedback than with a handheld graver, and if the slightest thing is about to go wrong, your fingers will know about it right away. As far as versatility, you are unlimited when turning by hand and the graver becomes an extension of yourself, constantly changing the angle of presentation. Especially when turning the delicate pivots, I may switch between cutting on center and cutting using the side of the graver like a "knife tool", several times in a couple of seconds. The last thing to consider is the surface finish. With a razor sharp graver, you can take 0.0001" off, at a relatively low spindle speed, and get a great finish. I think it must be a combination of the factors mentioned above that allow for this, but it really is extraordinary. Using the slide rest, I've found that much higher spindle speeds are necessary to get the same finish... and when you are talking about a diameter 0.0045", even 10,000rpm doesn't give you very much surface speed.

Having said that, I am sure that a very good balance staff could be made without any turning by hand... but it seems to me it would take at least as much practice and trial and error, and I'm still fairly certain it would be more awkward and time consuming than turning by hand (having to constantly change out tools, adjust heights/angles, etc).

I seem to remember Jerry Kiefer mentioning something about turning staffs on a Sherline, using only the machine slide... I think if anybody has done it successfully it would be him!

Very nice work! I've made a few, it usually takes at least two attempts for me to be successful. I cheat and flip it end for end to do the bottom half, just using the collet. Probably shows on the balance wheel, but it's been a while since the last one. I would get the pivots close to size and then use a ruby slip and fit to the jewels. Again, very nice work,

Wayne

Thanks Wayne! Many of the texts mention that method of reversing the staff in a collet, and if you have good collets that's just fine for larger watches without exotic timekeeping abilities. For true railroad grade watches or any COSC certified chronometer, that slight loss of concentricity would probably be an issue though. I think it will be a long time before I ever get my hands on any timepieces like that though! For now, I think it's just good practice for me to learn to do it in one chucking.

I take it you like those ruby slips? I've seen them, and have been tempted to purchase one, but wanted to hear firsthand info from someone who actually used one. Do you think they're worth the money? I have a coarse steel pivot file (which I rarely use, now that I'm getting good at turning the pivots close to final diameter with a graver), and a very fine home made steel burnishing file that I have been using so far. The burnishing file requires regular dressing, and it would be nice to have something that didn't require that upkeep.

[SteveM]

Nice!

You must use some pretty heavy magnification for that work.

Steve

[mars-red]

Nice!

You must use some pretty heavy magnification for that work.

Steve

Thanks Steve! Not as heavy as I'd like, unfortunately. I only have one loupe right now, and I think it's either 4x or 5x. I really need a couple of stronger loupes for this sort of thing. I do have a stereoscopic microscope that would be great to have mounted over the lathe for things like this... someday I should work on making a mount for it.