Bench-made screwcutting for a Geneva lathe?

Betzel

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I was reading the HJ this morning, and smiled when I saw this article.

Not sure this implementation make a ton of sense, but that has never stopped most of us. The article is available online (perhaps not permanently, but don't know) and it might make another interesting "someday" project. Also gives pointers from Levin's books that may be useful for other implementations of their screwcutting technique.

I saw an OEM version for one of these, think it was Steffan Pahlow, but that was an interesting chaser/tracer (Lorch) implementation. This one was on a Wolf-Jahn:

 

gmorse

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Hi Betzel,
The article is available online (perhaps not permanently, but don't know) and it might make another interesting "someday" project.
I think it will be available permanently in the BHI and AHS archives, but not necessarily to non-members of the BHI or AHS.

Regards,

Graham
 

Betzel

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Yep. For non-BHI members, if you're interested in doing silly things with a geneva lathe or screw-cutting stuff, grab it while you can.
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The Lorch implementation was from Steffen, but on a 10mm lathe. It's a very clever method, like making a duplicate housekey, but he has (of course) the special LLK headstock, patterns and cutting tools to do it this way. I have tried to duplicate old threads that nobody has cutters for, and it's not easy. The Lorch implementation is interesting as it guides a cutter on one end and uses a follower on a pattern on the other. Was not intended to make strange, ancient thread patterns, but would work for that if you could somehow follow an existing odd form. Make taps, etc.
 

wefalck

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Thanks for the link to article. Looks interesting.

I had contemplated for some time to make a screw-cutting attachment for my Wolf, Jahn & Co. 6 mm D-bed lathe, but then was able to put my hands on an 8 mm WW Lorch, Schmidt & Co. with original screw-cutting attachment. A few years later I was able to buy a complete set with matching numbering of all parts and sold off the first one. So no need to go for home-brew anymore.

A previous owner added a brass 90 tooth gear-wheel to the set, which is very useful for fine turning under power and I made an extension to the splined shaft, so that I can work on longer threads or around larger chucks. And I had to make a replacement knock-out bar for the dog-clutch. At some stage I should get a 120 tooth gear (the biggest that will fit) for real fine feed.

Thread chasing once was popular, particularly in the optical industry, where short threads are needed. On some of the lathes the spindle was moved, rather than the cutter. It would be difficult to make or find the thread cartridges and followers. Again some 20 years ago I was contemplating to find a thread-chasing attachment for the UNIMAT lathes and adapt it to my D-bed lathe.

More on thread-chasing lathes here: http://www.lathes.co.uk/chasescrewcutting/. Someone also adapted a Boley WW-lathe to thread-chasing: Boley watchmakers' lathes (scroll down on the page).
 

Betzel

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You have so many lathe attachments and accessories, it's amazing. Good thing you got started early, eh? Thanks for putting everything up on your home page, and for the help in copying some of it. Love the ship models and I'm warming up to tractors. I may even give in to the steam locomotives so many in the UK are fond of. Clocks, watches, it's all good fun.

My fear is that I will find a whole threading setup for my Leinen WW83. Then what? The set will only cut the standard threads, unless I make new wheels. The horological marvel is to make ancient fasteners from the days when nothing was standardized. I thought the chasing idea was interesting, mostly for these oddballs. So simple (ha!) to copy a pattern in theory, if you have one to follow?

At this point, not sure it's worth it just for standard threads. TBD.
 

wefalck

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Well, some 30 years of collection ...

It happened every so often, that I finally made an attachment and then shortly thereafter I found an original.
 

Betzel

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shortly thereafter I found an original.
The bus comes after you start walking, and it only rains when you have no umbrella?

Interesting, these guys made all of the gears from brass. I don't have a real mill, so this could perhaps be done for a larger lathe, though slowly. I have too many "someday" projects as it is...
 

wefalck

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P.S. on odd and obsolete threads: the Lorch set of change wheels includes wheels with 20-25-30-35-40-45-50-55-60-63-70 for a metric lead-screw of 1 mm pitch. As one can arrange them on the banjo in groups of two to four wheels, you can cut almost any odd thread with the right combination. The 63 tooth wheel is there to approximate inch-base threads (works pretty well for practical purposes, though a 127 tooth wheel would be more precise, but is too big).

The guys in the article used a module of 0.5 for the change-wheels, while Lorch used 0.8, which I think you need to transmit the forces, when you want to cut threads above M2 or so.

This reminds me of another modification/addition I made: I adapted a standard ball-crank with a shaft to fit into the draw-tube, where it is locked into place with a tapered pin. The common round-belt arrangement to drive the lathe just does not give enough torque for thread-cutting under power.

One can buy the gear wheels, in case one doesn't have the facility to cut such serious wheels.
 

Betzel

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Thanks for the post script. I did not know that about commercial gear wheels or the Lorch set, but knew torque in cutting was a problem. The videos I see "under power" show a number of shallow, repeat passes.

Does the tapered pin go in radially to the shaft of the drawbar, forward of the knob, with a small hole drilled in it, passing through the crank-shaft inside as well?
 

wefalck

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Unfortunately, the photograph below doesn't show the pin, I just realised, but yes, the tapered pin passes radially through the draw-tube and the the solid shaft of the hand-crank. I chose this option as minimally invasive for the 'historical' substance of the lathe and providing a positive key. It is located between the gear on the spindle and the knob. Actually, since the picture was taken, I replaced the hand-crank with a slightly bigger one to give more purchase.

LorchWW-new-72-20.JPG

I did some serious thread-cutting with it, for instance to replace the drive of the rotary table on my Wolf, Jahn & Co. miller and to make the y-axis spindle of my micro-miller composed from Lorch parts.
 

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