Imperial threads on a Metric Myford S7

Hallo

This question is usually asked "the other way around".

I am using a Metric Myford S7 with gearbox. I do have all the normal change gear wheels plus a 127 teeth wheel. Is there anywhere an instruction how to cut Imperial threads on a Metric Myford S7 with gearbox?

Thanks

Johannes

Martin Cleeve's book "Screwcutting in the Lathe" published by Workshop Practice Series has a chapter on turning imperial threads with metric leadscrew. It does not specifically address the gearbox models, but provides all the formulas, as welll as charts of change gears, that you could use the gearbox as the last pair of gears in the train and work it out. Or you could set the gearbox to cut a thread the same as the pitch of the leadscrew so regard it as 1:1 and construct your gear train accordingly.

But I am sure the topic has been discussed on this forum before so perhaps you might search around some more in old threads.

PS, this thread suggests you might be in luck and the S7 Metric in fact has an Imperial leadscrew and translator gears. Get rid of the translator gears and you have an imperial set-up. Not sure how the gearbox works out though!

**LINK**

The imperial to metric conversion uses the 127 on the leedscrew side of the equation ie 'driven' and is usually paired with a 100 driver (or 120 on some of the Chinese lathes)
For a metric leadscrew you want the 127 as a driver. It is often paired with a 120. The rest is just maths.

Is there not a chart on the inside of the gear guard ?

My imperial machine has one.

Phil

The "metric" Super 7 has an 8 tpi leadscew, and I imagine that the gearbox is completely standard too, so cutting imperial threads will be entirely straightforward without needing the 127 tooth gear at all. You would need it if you wanted to cut "perfect" metric threads on your "metric" S7, but in practice, at least for fastening, most metric threads can be approximated quite accurately enough on an imperial lathe. There are several threads on this forum referring to methods of determining the required ratios.

Thanks Everyone

I checked my S7 and it turns out that the leadscrew is indeed 8tpi (almost an imperial lathe in disguise).

Now it is all clear to me how to proceeds.

Johannes