Reverting An ML7 To Change-Wheels: Any Thoughts??

[Nigel Graham 2Participant @nigelgraham2]

I wonderedif anyone else has done this and whether they found it worthwhile…

 

Some years ago I treated my Myford ML7 to a second-hand, older-version gearbox; keeping all the original components including the leadscrew. I bought a length of stock ACME “studding” and made the appropriate, shorter leadscrew this pattern of gearbox needs.

This has suited my needs very well until I wanted to make several M6 studs recently, with screw-cut threads for more certain concentricity.

Unfortunately, the machine cannot now cut common metric threads, which even the standard change-wheel set will allow to close limits. (The cumulative errors even without a 127T wheel are not significant over many tasks’ thread lengths, such as studs.)

So I am pondering reverting to normal change-wheel operation for greater flexibility despite slower setting-up.

Has anyone else done this? Did you find it worth doing?

Or might I be better using dies with perhaps rather better die-holders than I have? (I have one of those commercial sets with a Morse Taper shank, but it really needs a tailstock that can accommodate tanged shanks, and is almost unuseable on an ML7.)

 

[DC31kParticipant @dc31k]

Would there be any possibility of changing the connection between spindle and gearbox input to facilitate metric?

A synchronous pulley and belt setup might offer possiblities that gears do not.

An option could be to change the leadscrew to metric, but the halfnuts require some deep thinking (Martin Cleeve talked about changing leadscrews in his book).

How interchangeable are the gearbox internals? On competition motorbikes, they use drop-in clusters to tweak the ratios to suit the circuit.

With 3D printing today, gear production has become a lot easier and you are not limited to standard DP or MOD sizes. Drawing software can also understand pitch shifting so fixed meshing distances are not a problem.

A second hand Super 7 tailstock could be a possiblity.

[JasonBModerator @jasonb]

I thought the usual practice was to swap the mandrel gear, 34T in the case of M6. As this chart shows you can get a pitch of 0.999mm which should be OK for a few turns on a stud.

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

Why do you need a tanged shank? My tailstock die holders don’t have shanks

[bernard towersParticipant @bernardtowers37738]

If you are cutting long lengths of thread would an ELS be the way to go?

[Dave WoottonParticipant @davewootton]

Have you had a look at the late Brian Woods book on screwcutting? There are very clear explanations of cutting metric threads on an S7B. I use them regularly with no problems, the extra two changewheels are available from Myford/RDG. I believe the method was originated by the late and much missed John Stevenson.

Book is still in print and available published by Crowood.

[Trevor Drabble 1Participant @trevordrabble1]

• Why not buy a pair of 33 and 34 tooth gears from Myford / RDG ?

[noel shelleyParticipant @noelshelley55608]

Is there not a change wheel conversion set for the quick change box to give metric threads ?  Noel.

[JAParticipant @ja]

I bought John Stevenson’s two gear wheel set up about 10 years ago but they did not fit my S7. The structure of the lathe got in the way. For a lot of money Myford will, or would, sell you a nice conversion kit. However all this comes with a warning: These conversions take some time to set up and then dismantle.

The easy option is to find someone with a metric lathe or use a die holder as you suggest. Both are cheaper and quicker that the gear wheel option.

JA

[John PParticipant @johnp77052]

I have changewheel S7 ,having a gear box machine is a limitation on
things that you may wish to do ,years ago i made some quide hobs
for a Quorn grinder which needed a piggy back extra quadrant and
more change gears in the train for some of these.
Even with the pair of 21T metric conversion set some of the setups
were inconvenient to change from one pitch to another.

On another recent thread on a worm gear the OP was looking for
a way to produce a worm using a box machine and was asking for
advice ,that thread has still not reached a conclusion.

For some while now i use a 127/60 tooth .8 module pair in the train,
they fit within the gear cover and make setting up much easier.
The photo here shows the setup for 1 mm pitch also a complete
chart for metric pitches.

John

[Dave Wootton]

On Dave Wootton Said:

Have you had a look at the late Brian Woods book on screwcutting? There are very clear explanations of cutting metric threads on an S7B. I use them regularly with no problems, the extra two changewheels are available from Myford/RDG. I believe the method was originated by the late and much missed John Stevenson.

Book is still in print and available published by Crowood.

Plus one for all this save that I think the use of alternative stud gears may well be earlier eg in vintage letters to ME.

[BazyleParticipant @bazyle]

All the metric pitches have a close imperial pitch that just needs a small correction. A few years ago in ME or MEW there was a simple lever system by Jacques Maurel to provide this correction. Probably once made it is quicker to set up than change gears.
If you take off the QCGB then all the imperial pitches will also be more tedious to set up, and for fine feeding between screwcutting.

[BazyleParticipant @bazyle]

Issue 4270 ME

https://www.youtube.com/watch?v=3wULa5aTPd0

 

[JAParticipant @ja]

If you take off the QCGB you have not got a lead screw. I fitted a gear box to an early S7. The first step was to shorten the lead screw by around 6″.

JA

[Robert Atkinson 2Participant @robertatkinson2]

OP says he kept the original leadscrew.
I went the Electronic Lead Screw route

Presentation

Robert.

[Dave Wootton]

On Dave Wootton Said:

Have you had a look at the late Brian Woods book on screwcutting? There are very clear explanations of cutting metric threads on an S7B. I use them regularly with no problems, the extra two changewheels are available from Myford/RDG. I believe the method was originated by the late and much missed John Stevenson.

Book is still in print and available published by Crowood.

I don’t know if Brian Woods book was ever updated but he was not aware that there was an earlier version of the S7 gearbox. Many years ago I pointed out to him that his book did not cover it and indeed gave the wrong impression. We discussed the possibilities of upgrading the early box (don’t try it) and he seemed quite upset that it could not sensibly be done to fit his book. For anyone who does not know (which includes some people on here) the only visual indication of the early box is that it has an aluminium cover on the tailstock end and runs at half the speed of the current one to cut the same thread which makes it a very different animal.

[Simon Williams 3Participant @simonwilliams3]

Easy peasy, but because you say you have the older gearbox you need a 17/30 compound pair and a 16/29 ditto.  Don’t buy a 33 and a 34, they won’t fit and wouldn’t give you the pitches you’re expecting.

This is covered in detail in a thread on the old forum.  I don’t know how to make the search function work, perhaps someone more adept than I can cross ref a link to a thread called “metric screwcutting on a super 7” – or something like that.  I’ll see if I can find it this evening, got to go out for the rest of the afternoon.  As well as detailing the logic this thread shows the actual error using these gears.

I think I sold my last set of these gears but I’ll have a look in the stores later on.

Rgds Simon – and my 16 – 1/2 toothed gear.

[DMR]

On DMR Said:

On Dave Wootton Said:

Have you had a look at the late Brian Woods book on screwcutting? There are very clear explanations of cutting metric threads on an S7B. I use them regularly with no problems, the extra two changewheels are available from Myford/RDG. I believe the method was originated by the late and much missed John Stevenson.

Book is still in print and available published by Crowood.

I don’t know if Brian Woods book was ever updated but he was not aware that there was an earlier version of the S7 gearbox. Many years ago I pointed out to him that his book did not cover it and indeed gave the wrong impression. We discussed the possibilities of upgrading the early box (don’t try it) and he seemed quite upset that it could not sensibly be done to fit his book. For anyone who does not know (which includes some people on here) the only visual indication of the early box is that it has an aluminium cover on the tailstock end and runs at half the speed of the current one to cut the same thread which makes it a very different animal.

Wasn’t there also an external gear at the tailstock end of the box?

Brian Wood was a great loss.

[Nigel Graham 2Participant @nigelgraham2]

Oh Hell’s Bells! I paused to read Jason’s citation and switching from one to the other wiped out this reply I’d started!

 

Thankyou – some interesting possibilities.

 

The verdict seems try different mandrel pinions. Otherwise put up with the lack of metric threading and use a decent tailstock die-holder that actually fits the lathe. My Harrison L5 will cut metric threads as it has a 127T wheel but it’s not really for teensy-weensy M6 studs!

NB: this is Myford ML7, with early-pattern gearbox, not a Super 7, so some suggested routes may not work anyway.

The Installation and Operating Manual for the gearbox- a lathes.co reprint – is confusing. It seems to suggest that it can cut module pitches up to 1mm pitch (not above), but using a special quadrant and a set of extra wheels, as well as the gearbox itself.

By which time you may as well use the standard quadrant and change-wheels anyway. An 8tpi leadscrew allows an M6 thread (1 mm p.) accurate to 0.1mm over ten turns, using only the 25-35, 30-55 wheels. Calculating for the other M-series from M3 to M27 (3mm pitch) show very close results for all, also by just 4 wheels with 5-tooth increments. Close enough for items like short-thread studs, anyway, perhaps finishing to profile with a die.

This from a spreadsheet I created for my EW 2½” lathe, with 8tpi screw, only a 2-stage banjo and 5T counts; but sadly the poor little machine is so worn it would not cut the M6 threads I wanted.

 

DC31k – I am afraid rebuilding the machine is neither feasible or desireable.

Nor is printing gears. I have no 3D printer and I struggle enough with basic CAD without diving into gear designing and CAD/CAM software.

It’s not possible to exchange the gear cluster as on a racing motocycle: it’s not a racing lathe.

 

Jason – Swapping the mandrel pinion for 34T looks the most useful route. I’d have to investigate further. Presently I have the 12/something and 24/something pairs; the former being that specified for the early gearbox.

Ah – the die-holder does have a tang. That may be the problem, preventing it gripping sufficiently in the tang-less tailstock to resist slipping. I could try skimming just a few thou. off the tang diameter. It’s an awkward blighter anyway on a small lathe like this with such a crowded saddle.

 

Dave, Trevor, Noel, JA – Which model of the Myford though, for the wheels you suggest? These lathes seem very fussy which gears will fit the driving end.

 

John P. – I know the discussion you mean. There of course is a worm: circular pitch so (not-nice-number)TPI! This is a problem facing me with a small horizontal mill’s table feed, but I have calculated a combination for my Harrison lathe and its (incomplete?) wheel set.

 

Ega – See above re lathe type hence possible incompatibility.

 

JA, Robert -I have indeed carefully kept the original leadscrew and associated displaced parts.

and Bernard – I’m afraid an electronic lead-screw is not feasible for me. I lack the requisite knowledge.

 

DMR _ There is another indication. The early box uses a shortened lead-screw running in a blind bush in that end wall, not a full-length screw through the whole box.

 

Simon – That looks hopeful, but again this lathe is an ML7 and the accesories for a Super 7 might not fit.

 

An aside: I looked at the Hemingway Kits gearbox for these lathes. It is a bit more limited still, lacking one or two standard threads.

 

 

 

 

 

 

 

[bernard towersParticipant @bernardtowers37738]

Nigel , didnt we all start without the requisite knowledge ?

[Simon Williams 3]

On Simon Williams 3 Said:

Easy peasy, but because you say you have the older gearbox you need a 17/30 compound pair and a 16/29 ditto.  Don’t buy a 33 and a 34, they won’t fit and wouldn’t give you the pitches you’re expecting.

This is covered in detail in a thread on the old forum.  I don’t know how to make the search function work, perhaps someone more adept than I can cross ref a link to a thread called “metric screwcutting on a super 7” – or something like that.  I’ll see if I can find it this evening, got to go out for the rest of the afternoon.  As well as detailing the logic this thread shows the actual error using these gears.

I think I sold my last set of these gears but I’ll have a look in the stores later on.

Rgds Simon – and my 16 – 1/2 toothed gear.

I believe this is the thread;

Myford Super 7 Metric thread cutting gears

Another possibility, retain the gearbox, and if you only cut a limited number of metric threads, seek out a Herbert/ Coventry die head & chasers.

Bill

[Andrew CrowParticipant @andrewcrow91475]

Nigel, my sliding die holder started life on a Harrison, sliding on the tailstock spindle it now has a morse taper holder which I find is OK for cutting threads with a die up to about 3/8 inch dia.

You could possibly make one that slides on the tailstock spindle using the existing keyway for the drive.

It’s a bit late now but I could send a couple of photos tomorrow if its of interest to you.

Andy

[Nigel Graham 2Participant @nigelgraham2]

Bernard – True, but I thought fitting electronic drives to an ML7 a very expensive and difficult route: stepper-motor, electronics, power-supply unit, a lot of mechanical engineering work to modify the lathe… I already struggle to finish anything.

However I did explore the subject. The only trustworthy source I could see among oodles of dubious E-Bay ads is a German manufacturer called “Rocket” or something like that. Its web-site, complete with photographs of typical installations on ‘Wabeco’ and other modern lathes, confirmed as above, that an ELS is not justifiable for the few metric threads I would need cut.

It did at least suggest I would not need electronics or programming skills I would find very difficult to learn.

 

Bill –  I read that article though didn’t follow the further references. Sixteen-and-half teeth? I’ve heard of square and elliptical gears working in pairs, but not wheels with fractional teeth! Presumably reality would be 33T and its mate also doubled…. if such wheels are available.  (Those odd-shaped gears give cyclic velocity variations.)

I’ve all the tables etc. but they require an “optional extra” banjo and additional change-wheels. Even if available, this seems a very inconvenient “half-way house” conversion.

So… back to using dies?

As it happens I have a Coventry Die-head and a load of chasers I assume for the same head. It looks too large for a Myford lathe but would be fine on the Harrison, although it has a plain, not Morse-taper, shank that might not be removeable to replace.

I’ve also a small die holder I think once part of an equivalent to a tapping-head, releasing at a pre-set point. I might be able to fit that up in some way.

Yes _ I would be interested in your photos, please. Attached here, they may help others, too.

 

Andrew – Interesting suggestion. The commercial die-holder set I have is not ideal, because the tailstock taper does not grip it very tightly and it relies on a long tommy-bar against whatever it can find, to withstand the rotation force.

Although intended for use on a small lathe like an ML7, it is a clumsy contraption making the machine very cluttered and the operation more awkward than it should be.

I have a little “Axminster” lathe, probably a Sieg C0 in disguise, which is fully metric but I’ve not set it up. With no clasp-nut and thread indicator, it is not really designed for screw-cutting despite a set of ‘Nylon’ change-wheels.

Ironically, if I want to screw-cut small metric threads, I may be best restoring my well-worn old EW lathe as I’ve long intended anyway. The volume of work involved, even I make a new spindle, may be about the same as fitting an ELS to the Myford – and far less expensive.

 

 

[Michael GilliganParticipant @michaelgilligan61133]

Nigel

As a latecomer to this discussion … I would just mention that [about 60 years ago] my Dad made a very simple tailstock die-holder for small-ish threads

Its heavily knurled Aluminium tube slid nicely on the tailstock barrel.

MichaelG.

[noel shelleyParticipant @noelshelley55608]

Thank you Michael, what a brilliant idea and so simple ! Noel.

[Simon Williams 3Participant @simonwilliams3]

Peak4 thankyou, that’s one of the relevant threads though the two older  threads it references give a 404 Page not available error.  No matter, most of the relevant information is included in the correspondence with Jesper Crone as per peak4’s link above.

Including an explanation of my wacky 16-1/2 tooth gear.  Which isn’t as wacky as it sounds.

One remnant question if I may.  Is the mandrel gear on a ML7 30 teeth same as an S7?  If not what is it?

Rgds Simon

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