Neil Wyatt's 63-tooth gear for mini lathe with 1.5 mm metric leadscrew

I have a SC3 mini lathe with a metric 1.5 mm pitch leadscrew and I want to cut Imperial Threads.
Unfortunately in Neil Wyatt’s Change Wheel Tables (article “Universal Thread Cutting on a Mini Lathe”, Model Engineers' Workshop issue 204) there is just the table missing for cutting Imperial Threads in combination with a 1.5 mm metric leadscrew using the 63-tooth gear. Or did I overlook something? Is there generally such a table available or do you know where I can get this information? Thanks, Wolfgang

Welcome aboard, Wolfgang

... Near the middle of the first page of that article, you will find the explanation.

... Short paragraph, just to the left of Fig.2

MichaelG.

Hi Wolfgang,
Neil has put data in the table to cut imperial threads using a 2mm pitch leadscrew. You just need to factor in the 3:4 difference in ratio and change one of the gears to suit. Another way to look at it is to multiply the thread TPI value you want by 3/4 (0.75) then use the entry from the table for the 2mm pitch leadscrew corresponding to that value. For example if you want a 24 TPI thread. 24 x 3/4 = 18 so use the entry for 18 TPI on the table for a 2 mm leadscrew.

Les.

Little Machine Shop Has a calculator here that lets you select the imperial or metric lead screw, imperial or metric thread to cut, and also allows you to add any transposition gears you may have, and gives the change gear selection meeded to cut the desired thread.

**LINK**

Chuck

I have had nightmares about this!

There is little information out there that is definitive but it appears the majority of mini-lathes have 1.5mm pitch leadscrews but some have 2mm pitch.

But... when I wrote the article I produced tables for both metric pitches, so I've uploaded them to a pdf (with the tables in handy print out and laminate style!) linked to by the article here:

**LINK**

I hope that helps,

Neil

P.S. an odd situation - a 1.5mm/2.0mm metric leadscrew fitted with a handwheel with a 60/80 division graduated collar will give you better 'thou' accuracy than anything you can fit to an imperial leadscrew (e.g. the 64 division wheel I have fitted to my 16 tpi leadscrew)..

Neil,

I know that "the Editor's decision is final" but I have to ask why you can't put 125 divisions on the HandWheel ?

MichaelG.

With an instinctive premonition of doom, when I ordered my (metric) Australian C3 minilathe I also purchased an imperial leadscrew as an 'optional' extra. It came with a whole bunch of new change gears and indexing chaser. It is a pita to swap but well worth the additional $110 (2006)

* Danny M *

Edited By Danny M2Z on 27/06/2014 17:15:58

> why you can't put 125 divisions on the HandWheel

I could. But I wouldn't be able to read them without taking my glasses off and sticking my nose down to lathe-bed level

Also, I hate numbering that has an awkward bit on the end, like the 75-division dials on my mill.

Neil

Neil.

Thanks for the article and gear tables, but some combinations could do with a bit of a tune-up to squeeze a bit more out of this handy little lathe. I downloaded the NThreadP program from the lathes.co.uk site and it seemed to better some of the gear pairs shown in the charts.

Cheers, Martin.

Hi Martin,

I think i said I was sure there could be improvements - I calculated them all with a spreadsheet and stopped when I felt I had sufficient accuracy for each thread. I think most, if not all, are within the tolerance for rolled threads and commercial screws, if not to micrometer standards!

Brian Wood is giving the tables a tune up, though.

Neil

Hi Neil,

Thanks for the feedback and update!

However, there seem to be some strange values e.g. for 28 TPI [50 35 20 63] (error -33.4 % !) or 36 TPI [50 65 40 65] (error 0.6 %) regarding the 1.5 mm metric leadscrew?

The Little Machine Shop calculator states e.g. for 28 TPI [35 55 57 60] an error of 0.036 % and for 36 TPI [35 63 55 65] an error of 0.061 %.

Obviously there are significant differences between the calculation methods and there seems to be a trial and error strategy appropriate...

Wolfgang

Hello Wolfgang,

You found the obvious mistake---couldn't miss it really!!

As Neil says, I looked over the tables and corrected the sort of error you found, there were some impossible gearing arrangements too which I also rectified. I did send them to Neil too but clearly the gremlins are powerful.

I can send you the whole lot by email if you send me your address, I don't think I have the patience to make jpgs of them all so that I can put them in my albums My address is [email protected]

If others would like these copies please get in touch. .

Regards Brian