Incorrect thread pitch

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 28/05/2021 07:08:07:

Zoom in on the photo I took it from Michael

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No need, Jason … I had already seen the shape

I just misinterpreted its intended meaning, because the resolution is rather low:

… similar problem here:

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… but, thanks to D Hanna, I can now interpret the text above V as reading dp

MichaelG.

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Ref. __ page 9 of this:

https://www.making.unsw.edu.au/media/uploads/Colchester%20Metal%20Lathe%20Master%202500_dQeKOzn.pdf

Note:  I was pleased to find the manual, because my Dad had a brand new Master 2500 in his workshop at Lancaster University, circa 1967.

Edited By Michael Gilligan on 28/05/2021 10:00:54

[JasonBModerator @jasonb]

Must be an ipad thing, mouse wheel on the PC gives a clearer image

[Howard LewisParticipant @howardlewis46836]

I said "Ignore the T I D" because that seemed to be causing concern for the OP, and prompted a discussion about which gear was required on the indicator.

I never bother with the T I D and always keep the half nuts engaged whether cutting Imperial or Metric threads.

It removes one possible source of error, in my view.

The important thing for the OP is to set up the 3:1 ratio between Chuck and Leadscrew, so that the 6 mm pitch Leadscrew advances the Saddle by 2 mm for each revolution of the Chuck..

Howard

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 28/05/2021 09:57:48:

Must be an ipad thing, mouse wheel on the PC gives a clearer image

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No … not an iPad thing, Jason … just a Michael thing

I followed your link, but didn’t then open the large version of the photo

… just zoomed-in on what you had linked.

MichaelG.

[JasonBModerator @jasonb]

Ah I think the url stays the same whichever image is being viewed, I was looking at the 4th one along of the headstock when I copied the link. Click that so it replaces the photo of the whole lathe and then click again to get a larger image without the bidding ended banner and then zoom. Hopefully you can zoom in the same with the touch screen.

[Michael GilliganParticipant @michaelgilligan61133]

No problem, Jason … all works fine

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

Posted by John Tumble on 28/05/2021 09:11:00:

You only need to keep the half-nut engaged if the leadscrew is imperial (and you are cutting a metric thread).

With a metric leadscrew, things are super easy and you can engage and disengage the half-nut whenever you like.

John

Alas that's not universally true! For example, a metric mini-lathe typically comes with 3 different gears for the thread dial indicator, and you certainly can't engage the half-nut at any point. My metric WM280 is different again. It's TDI covers the common pitches with two different match points and there are a few pitches, like 0.8, that the TDI doesn't cover at all. These are best cut by keeping the nuts engaged all the time.

Threads cutting on a lathe is one of the few areas where metric is clumsier than imperial; it's because metric threads are specified by pitch, not turns per. Nothing is perfect!

Dave

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