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Lathe Threading Dials - everything you ever wanted to know about them...

RobinHood

RobinHood

Ultra Member
Premium Member
Here is great video of how a lathe threading dial works, why there is a “problem” when threading metric on an imperial lathe (and vice versa). He shows a shop made combination metric/inch threading dial... He is an engineer, so you will see some math... Enjoy.

BTW, he has some other really cool stuff on his channel...

 
Thanks @RobinHood - just goes to prove that the "science guys" who just had to have the metric system made a few errors in their desperation to have a different system. If they had just went with a pitch like threads per centimetre instead of the distance in mm between threads ( all in that effort to avoid fractions) it would have been so much simpler.

I like his threading dial - would be a great tool for a metric built lathe. The metric Utilathe requires a wicked threading dial with gears you need to move ontot he lead screw to ensure engagement is correct - silly really


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Yes Sir!!

That beast is crazy! I saw it live once and ran - You are awesome for just having possession of such a device!!! LOL

I can see where it would be easy to mess up if you just engaged on the wrong letter once...was it A.......no B.......ooops ...C.....ahhhh crap.....
 
That is a very informative video & very interesting gadget he built. The metric lead screw to make inch threads is the inverse problem we have here in NAm - IMP lead screw cutting metric threads. Aside from the coincidental threads we typically have to swap gears to get a more complete range of metric pitches. That still leaves the familiar guidance of 'don't release the thread engagement lever' as he mentions. But even this has been debunked a bit. You can release the engagement if you follow a procedure. Here is link to Tom Lipton vid & article. I have yet to try this, metric threads are on the horizon though. But it seems straightforward watching the procedure.

http://conradhoffman.com/metricthreading.htm

 
My lathe came with a thread dial and I’ve used them and was good at using them (for a first year) but my number sticker moves and there is no literature about what mark to hit for what threads as the one I trained on had. Even my 7x12 had a dial and that was consistent likely because of the stamped dial. So that’s a future project
 
With my Southbend with 8tpi leadscrew and 32 tooth dial gear The dial has 4 markings And revolves 1 time for every 4 inches of leadscrew. For 8, 16, 24 etc you can close anywhere just like he showed in the video. For even numbered threads (they repeat every inch) you can close on any of the 4 marks. For odd number (even number every 2 inches) you can use opposing marks. Close on 1 and 3 or 2 and 4. For other threads its I don’t know.
I usually just close on #1.
 
Correction, I think all integer tpi can close on any of the 4 marks. Any xx.5 tpi have to be on the opposing numbers.
 
Both of my lathes have dials - with 4 numbered divisions and 4 without numbers. The little one can do only some metric threads - and you thread with nut engaged forward and back as this is standard non metric indicator. For big lathe it can do almost any metric thread - I think like 84 threads in total. Same gear box as https://www.grizzly.com/products/Grizzly-16-x-40-3-Phase-Gunsmithing-Metal-Lathe/G0509G

Also some modular and diametric threads with gear change for cutting stuff for worm gears.
 
Both the SM1120 and the Colchester have imperial lead screws. So they have the simpler, 4 number plus the half tick marks dials.

Regardless if metric or imperial, I always open the half nuts at the end of the cut. Just remember to re-engage at the same mark when threading in the “off system“ where the spindle needs to be reversed.
 
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