hallo from stoke-on-trent

i have owned a vicroy ex school lathe for some years and never hadto do THREADCUTTING problem is i haveto cut a 1.75 mm thread and my chart goes up in 50,s ie 1.50 2.0 2.5 and so on ,its 3mm feedscrew how do i work out the drive train for this thread ,is there some calculating gadget i can use.

Welcome along Graham, I have not got an answer for you but this should bump the question up to the top. I know some online charts may help but someone will be along to advise you.

Welcome to forum from West Mids

H

Welcome!

Don't know the lathe, so unsure if Gearbox or changewheels, so probably not very helpful.

Can it be configured to cut a 3.5 mm pitch thread?

If YES, is it possible to change the gear train / gearbox to halve the ratio between Chuck and Leadscrew?

If NO, it may be possible to use the same technique, of setting up for a pitch that is within capabilities, and then amending the drive train so get a 1.75 mm pitch.

In theory, my lathe cannot cut coarser than 3 mm, but by substituting a 30T for the normal 40T input to the gearbox, I was able to cut a 4 mm pitch when it was needed.

If you are cutting a M12, would it be easier to use a Die?

Howard

Will this help https://littlemachineshop.com/reference/change_gears.php

http://bilar.co.uk/cgi-bin/change-gear-calculator.pl

From lathes uk

Richard

hi and thank you for your help .just my luck the gear calculators dont work for my lathe sooo looks like a die [i bet thats expensive for one job ]

To quote Howard Lewis from a post in July last year on 07/07/2021 12:55:49 in response to a similar query:

*******************

Cutting a Metric Thread on a machine with a Metric Leadscrew.

To cut a 1.5 mm pitch thread on a machine with a 3 mm pitch Leadscrew , the driver could be a 20T driving a 40T on the Leadscrew, with an Idler in between.

To cut a 1.75 mm pitch, you would use a 35T driver, Idler, 60T, so that the Leadscrew rotates a little faster than in the previous example.

*******************

Does that not provide a quick solution?

John

Edited By John Hinkley on 11/02/2022 20:31:39

Graham,

Does your lathe bear any resemblance to the blue Viceroy that features towards the bottom of lathes.co.uk entry for Viceroy lathes.

One of the pictures of that lathe shows a setting plate that includes 1.75 as one of the pitches that can be set on there

Regards Bob D

hi guys first of all [bob d] nearly but mine has change gears but thanks anyway

john/ two of the gears i have not got 35t,60t thanks anyway

[that will teach me to drill holes without chcking]

For almost any die made give tracy tools a ring, It may not be that dear if a "standard" and their always very helpful and quick with dispatch. Welcome and Good luck. Noel.

Graham,

What gears have you got? Is there a 70T among st them?. If so you could be in with a chance but as Noel says check Tracy, Standards are but a few quid!

Bob D

bob d] gears i have are 16x2,18,20,28,32,38,40,44,48,66,80,100 stud gear 38,and 3mm leadscrew.

Hello Graham,

With the gears you have, a combination 28--idler--48 on the leadscrew will  cut a thread of 1.75 mm pitch

Regards Brian

Edited By Brian Wood on 13/02/2022 10:01:58

Brian, Graham,

I went to Church this morning and when I got back home my prayer had been answered. Thanks.

Bob D

Hello Bob D

Only too happy to help, it all helps in keeping the brain active, although as I am sure you will know, it is not a difficult calculation.

Regards Brian

You just have to calculate the ratio between the Leadscrew thread, and the one that want to cut, and then find a combination of changewheels to give that ratio. This may require one or more compound idlers between the Driving gear and the Driven gear on the Leadscrew

It easier if you want to cut an Imperial thread on a lathe with an Imperial Leadscrew, or Metric on a machine with a Metric Leadscrew.

Cutting A Metric thread on an Imperial machine, or vice versa, is likely to involve a 127T gear for an exact translation. Using a 63T gear may well introduce errors. But in many cases they are small (See Brian's book "Gearing Lathes for Scxrewcutting" for tables giving the errors for ma lot of gear trains )

Howard

mr wood ,thank you sir , i really need that book as me and math never get on ,wish id paid more attention at school instead of chasing girls lol......

Hello Graham,

Thank you, kind of you to say but be aware I wrote the book for a range of lathes having screwcutting gearboxes. But I think it makes what might be a rather dry subject a little more interesting and I hope it gives some insights into the logic behind it all.

The maths in your case is simple enough, Howard has described it well.

Amazon sell the book at affordable cost, the reference is ---ISBN 978-1-78500-250-2

Good luck with your excursion into screwcutting, it is rather satisfactory to watch the thread forming as you cut it.

Regards Brian