Gearing Myford S7

[Kenneth BiströmParticipant @kennethbistrom]

Hello everybody!
I am Kenneth, from Sweden, and I just bought a Myford Super 7 (metric) from 1961,with the Norton gearbox.
There seems to be a lot of knowledge here about the Myford. So here comes my first questions (or point me in the right direction):

I wonder what I would need to do with the gear drive to cut both metric and imperial threads?
Is there any difference between gearboxes (metric/imperial)?

Regards Kenneth

[Kenneth BiströmParticipant @kennethbistrom]

Gearbox etc

[Thor 🇳🇴Participant @thor]

Hi Kenneth,

Welcome to the forum and congratulations with your lathe. I assume you have the gearbox manual? Have you checked some of the previous threads on the theme? Here are a few:

***Link***

***Link***

***Link***

Thor

[Brian WoodParticipant @brianwood45127]

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

[steamdaveParticipant @steamdave]

If you are not already a member, I would recommend that you join the Yahoo group for Myford lathes.

https://groups.yahoo.com/neo/groups/myfordlathes/info

Lots of very helpful knowledgeable folk there.

Dave
The Emerald Isle

[Kenneth BiströmParticipant @kennethbistrom]

Thanks guys!

I have a manual but it seems to be missing pages, thanks Thor!

I don´t think the gearbox in metric, it was just a question. I think I have the metric conversion gears though. The slide feed screws are metric.

I will take some photos and I will also check out the Yahoo forum.

Regards Kenneth

[davebParticipant @daveb17630]

There are two versions of the Myford Series 7 gearbox, one for the UK and one for the USA (for Unified thread pitches, the text on the ratio label is blue.

Metric Myford lathes have Metric feedscrews. All Myford Series 7 leadscrews and gearboxes were Imperial.

Cutting Metric threads on these requires either the Metric conversion set or two or three non-standard gears which allow reasonable approximations.

[john fletcher 1Participant @johnfletcher1]

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

[Howard LewisParticipant @howardlewis46836]

Theoretically, to cut Imperial threads on a machine with a Metric Leadscrew, or Metric threads with an Imperial Leadscrew, you should use a 127T gear in the train. I had one for my ML7, but never used it!

A 63T gear will give a close approximation, (often used by owners of mini lathes) and as already said, there are other combinations which will produce threads of acceptable accuracy in the pitch.

Others, far more expert than I, will quote the best combinations.

My current Far Eastern machine has Metric Leadscrews, but includes a 120T/127T compound gear in the drive train to the Norton gearbox, enabling either to be screwcut.

Howard

[John HaineParticipant @johnhaine32865]

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.

[Brian WoodParticipant @brianwood45127]

Hello John,

That's actually a very good idea.

Blowing my own trumpet here, perhaps such a selector could include a reference to my book on the subject which includes lathes other than Myford and presents tables for many other pitches than just metric; there is also a full set of tables for the mini lathes for both languages.of leadscrew.

Brian

[Roderick JenkinsParticipant @roderickjenkins93242]

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 BiströmParticipant @kennethbistrom]

Thanks alot again guys!
What if a have different gears than the impereal model, a think the lathe is converted to metric with 4-5 different gears? How would I know?
I have a photo of the gears in my album.
Regards Kenneth

[Brian WoodParticipant @brianwood45127]

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

[Roderick JenkinsParticipant @roderickjenkins93242]

Kenneth,

Your pictures look like the standard imperial set up so the single gear replacement should work. The official Myford metric conversion set **LINK** will give you a theoretically more accurate result but for the expense and hassle in setting up I do not think it is worthwhile. I do use mine for making more unusual leads for helical gears (or candlesticks!) but I was lucky to get it and lots of gears with the lathe. The original table I published some years ago did have a typo in the fine feed table but I have now corrected that.

Rod

[Neil WyattModerator @neilwyatt]

Posted by John Haine on 23/11/2017 10:55:05:

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.

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

[Piero FranchiParticipant @pierofranchi37209]

to hijack this topic a tad if you dont mind,

but what are the set of gears one used to be able top buy ????

I happen to get a full set of metric gears with my imperial super seven (with screw cutting gearbox)

[steamdaveParticipant @steamdave]

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

[Nick HughesParticipant @nickhughes97026]

Here's another set of tables, that cover a lot of extra pitches and TPI (goes down to 0.20mm pitch for M1.0 Fine)

http://www.model-engineer.co.uk/wp-content/uploads/sites/4/documents/gear%20errata%20tables.pdf

Nick

Edited By Nick Hughes on 24/11/2017 09:39:28

[Roderick JenkinsParticipant @roderickjenkins93242]

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

[steamdaveParticipant @steamdave]

Thanks Rod

Should have studied the chart more closely. And I've had the cataracts removed !

Dave
The Emerald Isle

[Brian WoodParticipant @brianwood45127]

Posted by Piero Franchi on 24/11/2017 07:57:46:

to hijack this topic a tad if you dont mind,

but what are the set of gears one used to be able top buy ????

I happen to get a full set of metric gears with my imperial super seven (with screw cutting gearbox)

Hello Piero,

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

Regards Brian

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