Hello Kenneth,

Welcome to the Forum, I feel sure you will find it helpful and interesting

To answer your question. Are you quite sure your S7 is equipped with a metric gearbox? To my knowledge Myford never made a metric version nor for that matter fitted those lathes with a 3 mm pitch leadscrew to match up

You might be referring to cross slide and top slide feed screws, there are metric versions of those.

If you can post a picture of the gearbox pitch plate it would settle the issue. To do that you create an Album of your own into which you install pictures or print and then post that material onto the forum thread.

Regards Brian

Hello Kenneth, to cut most Metric course threads you will need three extra gears25,33 and 34 these are readily available £9.5 each from Myford here in UK. Also there is a small device which permits the bango to drop further down to fit even more/larger gears to extend the thread cutting range. This home constructed devise was the subject of an article in Model Engineer Workshop some time ago, I have the article. I also have a table showing which gear to fit and which gear box settings you need to cut a particular Metric thread. If send me your email address via a personal message I might be able to help you. John

This question of cutting metric threads on an imperial lathe comes up so often that it deserves some prominence here so that people can see the answer without having to ask the question, so to speak! Is there any mechanism for doing such a thing on this website? Ideally a button that would take the reader to a page that brings together the best advice on how to set up the lathe, the change wheel combinations for the various common threads, the tables that people have produced showing all the pitches available for common change wheel tooth counts, and maybe the simple maths behind how to work out the best combinations. Also of course the magnitude of the errors (generally very small) that the approximations produce.

As alluded to above, the simplest way of cutting metric threads on a gearbox equipped S7 is to replace the 24 tooth output gear from the tumbler reverser (Stud) with one of the gears in the table below:

Hope this helps,

Rod

Edited By Roderick Jenkins on 23/11/2017 15:57:26

Kenneth,

The 'stud' gear that Rod listed in the table above is the only one you need to change. You match that with the gearbox selection to get the result show. I have a feeling that one of these is in error, but can't remember which, maybe someone else can.

Your gearing set up in your photos is shown arranged for fine feed. For screwcutting reverse the 57/19 cluster gear held in place with the swinging latch

If you have the metric attachment with the gears shown in your picture 2 you need to change the whole banjo and remove the wide 72 tooth gear to replace the set up to get metric results; you can see the attraction of the simpler set up in Rod's table without having to go through all that business as it also denies the fine feed arrangement.

Regards Brian

How to guides for both Myfords and Mini Lathes linked to on the 'Processes' page:

Processes

Normally reached from the workshop –> processes on the black band above.

The mini-lathe one includes the maths (I know 'cos I wrote it).

Neil

Question for Rod – or others:

The smallest metric pitch with the simple gear change a al table above is 2.0 = M15, which is quite coarse for my likely usage. Is there a way to cut smaller pitch metric coarse threads with a simple gear change? M10 – M2 is probably the range I would likely need to cut. OK, M2 – M5 would be by dies, but it would be good to know if it could be done.

Dave
The Emerald Isle

Dave,

The left hand column refers to the diameter of the screw and the next column is the pitch for the most common ISO metric fastenings so the table does go down to sizes that I would be unlikely to actually try to cut (doubly so for the BA sizes)

cheers,

Rod

Hello Piero,

I don't understand the question, can you expand on it please?

Regards Brian