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

[JasonBModerator @jasonb]

My various tailstock die (and tap) holders are not keyed to their shaft. It is just a case of firmly gripping the body and letting go when the thread is long enough.

[Tony JeffreeParticipant @tonyjeffree56510]

I have an ML7 that came with a full set of changewheels and a QC gearbox – for the reasons stated in the OP, I decided to convert the lathe to CNC operation and now have ELS and Mach 3 control available, which provides any thread pitch at the touch of a few buttons, also any fine feed rate that I may need. I wouldn’t go back to the faff of using changewheels.

[Michael GilliganParticipant @michaelgilligan61133]

The purist in me is still hoping to find one of these:

https://lathes.co.uk/bryantsymons/

MichaelG.

.

Edit: … I have just located the relevant patent and informed GoogleAI

https://worldwide.espacenet.com/patent/search?q=pn%3DGB111693A

Astonishingly … it thanked me 🙂

[Michael GilliganParticipant @michaelgilligan61133]

.

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[John PParticipant @johnp77052]

Hi Michael

From your last post some useful details in a Lindsay Publication
Precision lead screws ,gears and pantographs
can be found here.

 

https://archive.org/details/precisionleadscrewsgearsandpantographsbymachinerysindustrialsecrets/mode/2up

 

John

[Michael GilliganParticipant @michaelgilligan61133]

Excellent, John !

… Thank You

MichaelG.

[Andrew CrowParticipant @andrewcrow91475]

Hello Nigel, this is my die holder

It works OK on my S7 and my previous ML7 I have holders for any size die I have and it is also used to hold my 1/2 inch and 5/16 Coventry die heads.

Andy

[Andrew CrowParticipant @andrewcrow91475]

I meant to say that instead of using a morse taper adapter you could bore the brass holder to suit the Myford tailstock spindle and fit a key to provide the drive.

Andy.

[duncan webster 1Participant @duncanwebster1]

I would have thought that having a key to resist the torque would increase resistance to axial movement, resulting in even more pitch error. Mine is like Jason’s,  prevent rotation by hand, then let go when it’s long enough.

[Andrew CrowParticipant @andrewcrow91475]

The key doesn’t have to be a tight fit, just enough to provide resistance to rotation. I’ve been using that one for 60 years without any problem.

Andy

[Nigel Graham 2Participant @nigelgraham2]

I’m not sure where “pitch error” comes in with taps and dies. That had arisen in the Bryant-Symons article. A slightly over-cut or under-cut thread is the more likely problem; but taps and dies are not intended for microns precision.

The die holder I have is somewhat similar in principle to Andrew’s but uses a cross-bar through slots and a hole.

I also have a tapping-head generally on a bench-drill with Morse taper spindle; but it would work on a lathe with suitable tailstock.

 

Summarising so far from the many responses and conversations they evoked:

 

1) Electronic lead-screw drives: I can see their attraction, but they mean extensive modifications to fit bulky auxiliary machinery. Likely not feasible for me, and tangential to my original question.

Verdict: Discount.

 

2) Alternative gears between mandrel and gearbox: Seems to entail swapping change-wheels, and those on a special banjo.

Verdict: Investigate but probably Discount.

 

3) Gearbox modification: It can not be modified.

Verdict: Discount. I don’t think the suggestion, based on motorcycle-racing experience, was serious anyway.

 

4) Exchanging the lead-screw, clasp-nut and thread-dial according to the task: More awkward than swapping change-wheels, and incompatible with the gearbox. I’d need make these parts, too.

Verdict: Discount.

 

5) Reverting to original change-wheel system. That was what I asked about!

Against – as Tony Jeffree points out in supporting electronic drives, it revives the faffing, but the only really awkward part is access to the banjo clamp-screws.

For – Straightforward. Maximum thread diameter… large, both internal and external. Maximum pitch 1/8″ / 3mm; Maximum range of pitches up to that limit using the standard wheels. A 42 or 63T wheel would increase this facility by approaching the 127T effect. Myford lists 100T and 127T wheels anyway.

Verdict: Increases the lathe’s versatility, reduces convenience. Consider Carefully.

 

6) Keeping the gearbox etc, and using better tap and die-holders and/or die-head for small threads:

Against – Thread diameter limited.

For – Simple (no expensive, difficult, bulky modifications). Allows more or less any thread below perhaps 5/8″ or M16 diameter, or a bit larger, depending to some extent on the material.

Verdict: Maintains the gearbox’s convenience, but allows no metric screw-cutting. Consider Carefully.

 

Essentially the choice is between Options 5) and 6).

My original question was: Has anyone done it, and did you find it worthwhile?

 

A fellow club member told me he reverted his lathe to all change-wheels and did not find it significantly harder to use; but I think he standardised a lot of his own work around Brass Threads (26TPI).

[DC31kParticipant @dc31k]

FWIW, I think that somewhere a design has been published for more ergonomic banjo strumming on a Myford as well as quicker use of the change gear studs.

Finding that might add to the conversion basket weight.

[JasonBModerator @jasonb]

An ELS is not adding bulky parts to the lathe, whole lot would take up less room than the existing gearbox. Encoder is about 40mm dia and 40mm long. Motor no bigger than a jam jar and a control box the size of a tobacco tin, couple of pulleys no bigger than existing gears.

Question is how many times in the last 5 years have you needed to screwcut threads that have not been available from your existing gearbox? Second question is how many times have you been able to use the gearbox to screwcut?

That will be a big deciding factor. If you are using the gearbox weekly ( that includes changing feed rates) then having to use change gears may become a pain. If you have on;y had the need to do a few small metrics in that time then a homemade* die holder will be simpler than going back to changewheels.

Dieholder need only be a piece of silver steel held in a tailstock chuck or collet and the body just a short length of bar with hole for dies at each end and a few scews. Knurl and or add a tommy bar hole and away you go. That second video is a home made one to take metric OD dies and run on my old imperial dieholders shaft.

 

[Nigel Graham 2]

On Nigel Graham 2 Said:

I’m not sure where “pitch error” comes in with taps and dies. That had arisen in the Bryant-Symons article. A slightly over-cut or under-cut thread is the more likely problem; but taps and dies are not intended for microns precision.

[…]

My apologies for the distraction, Nigel

MichaelG.

 

[Michael GilliganParticipant @michaelgilligan61133]

No idea what’s up with the forum … I have tried five times to post this apology !

[Grindstone CowboyParticipant @grindstonecowboy]

There appears to be a problem with large swathes of the internet today, a friend has not been able to access at all, and I have had continuing issues trying to make payments. So it might not be this site’s fault this time.

Rob

[Nigel Graham 2]

On Nigel Graham 2 Said:

I’m not sure where “pitch error” comes in with taps and dies. ..

Try cutting a long thread with a die in a normal die holder, then compare the tpi with a commercial bolt which has a long thread. I was surprised at the difference. I think it is something to do with the thread you’ve just cut being the only thing that is driving the die forward on the rod, but the teeth which are doing the driving are cutting teeth. Any extra resistance to forward motion, for instance a key, must make if potentially worse. If a key is resisting rotation, friction twixt key and keyway will resist forward motion.

My production engineer friend used to have a die holder which fastened to the saddle, which he then drove forward using the leadscrew

 

 

 

[duncan webster 1Participant @duncanwebster1]

I’ve just written a screed on pitch error and dies, pressed submit, anx it disappeared. I fear you’ll have to manage without my pearls of wisdom 🙂

[Michael GilliganParticipant @michaelgilligan61133]

They are picking-us-off one-by-one, Duncan 🙁

MichaelG.

[duncan webster 1Participant @duncanwebster1]

Nil illegitimi carborundum

[Nigel Graham 2Participant @nigelgraham2]

DC31k –

Interesting… I have often wondered if the set-up can’t be improved. One snag is access to the Allen clamp-screw that makes the banjo grip the leadscrew journal. It is partially obstructed by the rim of the casing. One could trim the casing flange so the key can enter it axially, but that would create an aperture for swarf and dust to explore.

 

Jason –

Good summary.

My impression of ELS systems came from that German manufacturer’s web-site, and recalling various conversions that have been posted on this forum. The advertisement seemed illustrated by lathes larger than a Myford ML7, which can be quite cluttered at times as it is. Though I think these were 2-axis conversions.

I have now cut quite a number of threads using the gearbox; a mix of UN, BSP, Brass, ME, BSF and BSW, though only small numbers of each and at very irregular intervals.

I last used it only this evening, but for a fine feed, not thread cutting. I don’t normally worry much about feed rates except on bearing surfaces, but set them fairly fine anyway.

 

So from all the options discussed here, the overall advice really is keep the lathe as it now is, and develop a decent die-holder / die-head set for small metric threads.

 

If I want to cut big hefty metric threads, I might be able to use the big hefty Harrison lathe. My question arose from wanting to make some small, preferably screw-cut, studs and finding my EW lathe too badly worn for the task – although its change-wheels offer surprisingly close calculations for the main M-series pitches.

 

(If the gearbox fails at least I can replace it with the original system. The one on there now is actually Number Two, after I accidentally broke the first, also of the early short-leadscrew pattern. It may be saleable for “spares or repair”, but the replacement gear clusters are expensive.)

[Robert Atkinson 2Participant @robertatkinson2]

In case you missed it in the messages, have you seen this Electronic Leadscrew?

Presentation

I bought the single axis version. Yes you have to souce a stepper motor, drive and power supply separately but that is just building blocks and not unreasonable given the wide range of lathe sizes the system can be fitted to.

Robert.

[Michael GilliganParticipant @michaelgilligan61133]

I recall you mentioning the purchase, Robert

Does it meet your own high standards, or have you needed to improve anything ?

MichaelG.

[Robert Atkinson 2Participant @robertatkinson2]

It seems fine. I certainly could not do the maths required in the code. Only one comment is it’s not fluid tight but that can be fixed.

[Nigel Graham 2Participant @nigelgraham2]

Rather apt after all this that I had to resort to using a manual die-holder on the lathe this evening.

I needed make a special 4BA stud – I would not try screw-cutting such a thing, so took out my commercially-made tailstock die-holder in its elegant wooden box.

Only to find its mandrel and the large pin-punch supplied as the anti-rotation “key” are missing.

So too, is the small die-holder for the EW lathe.

Things are never missing until you need ’em, then it’s as if they never existed.

Back to the usual technicque: manual die-holder guided along the work by following it along with a drill-chuck in the tailstock while pulling the headstock belt round by hand. One handle of the die holder restrained by the top surface of the saddle.

[Author]

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