Screw cutting on a Stringer EW lathe

Hello all. I have just joined your group. Yesterday I bought a Stringer EW at an autojumble. It appears to be in good condition and came with a motor and most parts, including a set of gears for screw cutting. I have searched the internet for advice on how to set the gears for screw cutting and posts on the Model Engineer website keep coming up but so far I have not found one that helps me set the gears. I an fairly sure that someone has written a piece on this but I cannot find a thread on it. Could someone point me in the right direction please?

Hi Eddie,

Welcome to the forum. There was a thread on the forum about the Stringer EW lathe, see here.

Thor

Edited By Thor 🇳🇴 on 16/07/2023 19:26:02

Your starting point will be to determine the pitch of the leadscrew, all else follows from that..

Thor,

Thanks for highlighting the thread. I read the posts for about three years , from 2011 to 2013. There is lots of info on installing clutches on the lead screw and on possible use of a stepping motor. I c9uld not see anything about the basic arrangement of setting up gears for screw cutting though. I understand that some EWs had a diagram on the inside of the gear cover. But m8ne does not.

Doiogenesll,

The pitch of the lead screw is 1/8 ", in other words 8tpi.

Sorry about the typos - @and mis spelling your name Diogenesll.

Yours came with gear cover? That's a rarity! Mine has all the optional-extras but that.

Setting up for screw-cutting is as on any lathe with change-wheels, but limited to two options:

Spindle pinion - idler - leadscrew wheel;

and

Spindle - intermediate driven wheel + intermediate driver - leadscrew.

They cannot be set for fine feeds - were never designed to be. And the single-piece nut means you need reverse the machine for the next cut. For cutting short threads it's probably best to use a mandrel handle, with the motor safely isolated and the drive-belt slacked off, and back-gear engaged.

Other than that they will cut a goodly range of threads properly, and with a lot of trial-and-error calculations, quite a few others to fairly close limits over a short ( <10 turns) length.

The standard formulae apply:

Leadscrew tpi (8 on these lathes) / thread to be cut = Spindle pinion teeth count / Leadscrew wheel teeth count;

OR

That but LS / work = (spindle / 1st stud wheel ) X 2nd stud wheel / LS wheel.

So for 16TPI:

8/16 = 20/40

and for 26TPI:

8/26 = 4/13. Multiplying by 5 immediately gives 20 / 65. (I think the EW change-wheels include a 65T wheel.)

So 20T spindle, any convenient idler on the banjo stud, 65T wheel on the leadscrew.

.

For 32 tpi you'd need a compound train:

8/32 = 1/2 X 1/2, e.g. by 20T spindle, driving the 40T wheel on the stud, that combined with the 30T wheel that drives the 60T leadscrew wheel.

i.e. 8/32 = (20/40) X (30/60).

The intermediate two wheels are linked by a little driving-pin in the hole next to the wheel's shaft-bore. (Myford and bigger lathes tend to use a key for that.)

.

You'll find these calculations in almost any book on turning that deals with change-wheels, and it's just a matter of adapting them to the change-wheels you have.

Cutting mm threads would be more of a challenge, but not insuperable. Some will calculate near enough for removing most of the metal by screw-cutting and finishing with a die in a tailstock die-holder. Though for small threads (<M6) it may be easier to use a die anyway.

If you need augment or replace any of the change-wheels be careful as most modern gears are of 20º pressure-angle. Those on older machines like the EW Lathe may be of 14ºp.a. They will mesh, if the same pitch, but not properly, risking harming both.

NB: It is very bad practice to try to cut threads the same or coarser than the lead-screw, especially on a small, rather delicate lathe like the EW. It puts very unfair stresses on even a large machine.

It can be done with care on a larger machine by driving it manually, from a leadscrew handwheel, but I would advise nothing coarser than 12tpi, maybe 10tpi (1" BSF), and with very light cuts on the EW.

'

Some owners have adorned their elderly EW lathes with all sorts of elaborate modifications like stepper-motors, but I prefer to keep my older machine-tools as original as possible. If I want that sort of sophistication I'd buy a sophisticated machine, but each to his or her own!

Nigel,

Thanks very much for this useful information. It sounds like I should buy myself a book on lathe work. I did some lathe training 47 years ago but I need a refresher. Meanwhile I will now start experimenting.

Regards

Eddie

Try this site for a various ideas on EW lathes and mods if you want for improved screw-cutting

http\\modelengineeringnorge.weebly.com

There is a screw-cutting table for EW on the site (I would post it here but it is too much of a bloody faff)

M.

(had a memory refresh!)

note this is for the original 16DP change gears (why 16  wtf? had they lost the smaller cutter?)

Edited By Martin of Wick on 17/07/2023 09:00:26

Edited By Martin of Wick on 17/07/2023 09:02:44

Nigel has pretty much nailed it for you Eddie.

The leadscrew is 8tpi and I also screw-cut only using a mandrel handle (as I have not done the dog-clutch mod). I use my EW mostly for small brass work and generally use dies held in a tailstock holder but even so sometimes will half screw-cut a thread and finish it with a die - I seem to get better results with fine threads that way. It is also useful for anything where I don't have a suitable die handy.

I'd recommend you get "Screw Cutting in the Lathe" by Martin Cleve.

Regards,

IanT

PS  I've got an EW section in my photo album that may  (or may not) be useful   

Edited By IanT on 17/07/2023 09:09:44

Not a ‘lathe-work’ book per se, but a/the book by member Brian Wood seems to be a useful tome (but neither particularly large or weighty!) for sorting out all sorts of thread cutting settings/scenarios. I’ve not read it but his book regularly receives a hearty recommendation on the forum.

Thank you Martin for that table, which looks as if from the original EW Stringer manual for the lathe.

(Not for the daft comment you added though: 16dp seems a perfectly good size for it. Though if you build a set of finer DP whee;s, say 18 or 20DP, it may allow a larger range for finer threads.)

Eddie,

If you PM me an e-post address I can send you my calculations-table, an 'Excel' spreadsheet that also gives close-match mm combinations with the pitch-errors. The small mm threads are probably more easily cut directly with a die though.

The table also gives the identifiers for their corresponding thread types, e.g. 16tpi is 3/8" BSW & 1/2" BSF.

I should say I have not tried many of them in practice, tending to use a Myford ML7 as my work-horse while my EW lathe awaits refurbishing, so some might give diameter-conflicts needing re-calculation.

If you are au fait with 'Excel' you can edit it to create printed reference tables for the workshop - unless the system turns it into one of those wretched "xlsx" files!

Where the idler wheel is used, place a suitable spacer, e.g. a much smaller change-wheel, between the idler wheel and the retaining-nut.

Edited By Nigel Graham 2 on 17/07/2023 12:48:14

Well precisely, not so much for finer threads but a more compact gear train using less material and better matched to the size of lathe, as well as the facility for a more reasonable fine feed using 70-80 tooth gears.

However, for the enthusiast, the Norwegian engineer site provides a good explanation and mod for a banjo that allows double compound using DP16 but needs more 65s for a fine feed(which could be 3D printed).

'Course, the big PITA that makes using this lathe rather tedious is really the full nut. I have seen solutions, but none have appealed to me as being particularly reliable.

So on account of 'elf n safety' to avoid RSI, my EW doesn't get used as much as it should be!