MEW 186 – Electronic Lathe Control

[DerryUKParticipant @derryuk]

I enjoyed TJs article but rather than have an electronic box do the work is there any software (prefferably Linux so free) that will do the same using a PC?

 

Derry.

[DerryUKParticipant @derryuk]

[John Stevenson 1Participant @johnstevenson1]

Do a search for EMC2 on Google.

Like Linux completely free.

 

John S.

[Billy MillsParticipant @billymills]

It is very sad to see ten pages devoted to a crude ELS which is so dependant on spindle speed. ONE pulse per rev !!! Any screwcutting lathe has the complete answer, mechanical gears, the ultimate digital division/multiplication system for the home workshop, always phase locked when the nuts are closed and no starting up/bandwidth / Nyquist issues.

 

Billy.

[Ian PParticipant @ianp]

I’m with Billy on this one!

 

I had been aware of the term ‘ELS’ for many years but never investigated the forum. I just assumed it was a leadscrew only version of CNC conversion and it never got my attention.

 

I cannot imagine anyone would spend so much and go to so much trouble to cut a thread by such a flawed method. Even if the pitch was accurate enough for the job in hand, techniques like cutting a thread close to a shoulder would be fraught with difficulties.

 

I am slightly surprised that the author, a knowledgeable and skilled person could consider that this was a viable alternative to a full CNC system.

 

Ian P

[DerryUKParticipant @derryuk]

Why do people have to whinge and moan so much on this forum.

 

Don’t tell me about the things you don’t like, start your own thread and tell me about the things you do like.

 

Derry.

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by Ian P on 21/01/2012 09:14:11:

I’m with Billy on this one!

 

I had been aware of the term ‘ELS’ for many years but never investigated the forum. I just assumed it was a leadscrew only version of CNC conversion and it never got my attention.

 

I cannot imagine anyone would spend so much and go to so much trouble to cut a thread by such a flawed method. Even if the pitch was accurate enough for the job in hand, techniques like cutting a thread close to a shoulder would be fraught with difficulties.

 

I am slightly surprised that the author, a knowledgeable and skilled person could consider that this was a viable alternative to a full CNC system.

 

Ian P

Ian –

 

I am slightly surprised by your (and Billy’s) reaction – it makes me think that you didn’t read the article fully.

 

Firstly, ignoring the screw cutting for a moment, the two devices described are very definitely a viable alternative to a full CNC system for some uses, and likely a good proportion of the uses that the average hobby user would want from them. And for many, the fact that these are self-contained devices that don’t require any knowledge of PCs, G-code, CAD/CAM, etc. make them doubly viable.

 

Secondly, as I pointed out in the text, the screw cutting capability can be used to cut acceptable threads, within the limitations of the stability of your spindle speed and the one pulse per rev encoder. If I put my ML-7 into back gear, the increase in torque at the spindle is such that the spindle speed is rock solid, and it cuts threads just fine. In reality, on my lathe, with its 1/2 horse motor and V-belts, putting it in back gear is pretty much a requirement for threading anyway, to avoid motor stalling and/or belt slip.

 

Thirdly, cutting up to a shoulder is rather easier with one of these devices than it is under manual control, and no less easy than under full CNC, because the controller stops the saddle feed at exactly the right point, retracts the cutting tool, and returns to the start point for the next pass, with precise repeatability.

 

Regards,

Tony

[Ian PParticipant @ianp]

Tony

 

I think I was rather hasty in focussing in on what I thought were weak points without thinking it through, I accept also that with precautions taken to overcome the shortcoming (back gear, low speed etc) threads suitable for almost everything other than feedscrews could be created.

 

Do either of the systems you describe have an option to use a shaft encoder with many more pulses per rev? Presumably that would improve the accuracy.

 

Ian P

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by Ian P on 21/01/2012 12:44:47:

Tony

 

I think I was rather hasty in focussing in on what I thought were weak points without thinking it through, I accept also that with precautions taken to overcome the shortcoming (back gear, low speed etc) threads suitable for almost everything other than feedscrews could be created.

 

Do either of the systems you describe have an option to use a shaft encoder with many more pulses per rev? Presumably that would improve the accuracy.

 

Ian P

Ian –

 

A shaft encoder would certainly be a better starting point, but neither device is capable of dealing with anything more than one pulse per rev unfortunately. They are both designed around relatively low cost, low (computing) power single-chip microcontrollers that simply don’t have the processing power to handle a higher pulse rate (bear in mind that they would need to be able to handle the shaft encoder in addition to the existing one pulse per rev encoder, as the latter is used as an index pulse that indicates the start of a new rotation – even if you just increased to 2 PPR, you would still need the 1PPR signal as well). Interestingly, Mach 3 is also limited to using a 1 PPR encoder and suffers similar problems when the spindle speed is not stable. However, EMC2 can handle a shaft encoder and by all accounts gives good results even with relatively low counts per rev. There is a Youtube video that shows a Myford lathe being turned by hand & the EMC2 software is handling it perfectly: http://www.youtube.com/watch?v=AW5-A_ru3-I

 

Regards,

Tony

Edited By Tony Jeffree on 21/01/2012 17:43:10

[Michael GilliganParticipant @michaelgilligan61133]

That’s a very impressive video, Tony.
… Thanks for posting the link.

MichaelG.

P.S.

For anyone interested in the history of ELS …
http://homemetalshopclub.org/projects/electronic_lead_screw/els.html

Edited By Michael Gilligan on 21/01/2012 18:09:27

[Ian PParticipant @ianp]

Tony

 

I liked that! (the video demo)

 

Coincidentally I am planning to make some parts in EN24T with exactly the same thread M45x2. I just know its going to be a slow job, so this ELS stuff is starting to appeal to me.

 

Ian P

[Billy MillsParticipant @billymills]

Many people have used an ELS as a halfway point to CNC conversion. However I would maintain that if you have a lathe in half decent condition it is already very well equipped for screwcutting. If the machine reverses easily then a lift up toolholder makes screwcutting a quick and certain process without the added electronics.

 

My comments on 1 pulse per rev is based on a lot of experience in analog and digital phase locked loops. When sampling at such a slow rate the controller is given too little data. At a spindle speed of 600 rpm ( which many would think quick for thread cutting) that is only 10 pulses per second. Using a bull gear tacho would put the rate up by around 50 times greatly improving the loop dynamics- that would be very easy to do and could be a simple one time set up parameter. A 2 mS interupt rate should not be an issue for any decent controller but would make stepper rate setting easier.

 

Single axis control works very well in some applications- as Tony has proved with his Divisionmaster controller. That makes sure that you don’t loose count when the phone rings and gives all you could want in division options and resolution, if you do much dividing it is a godsend.

 

However while you are fitting a stepper drive and controller you are very close to full CNC which then gives vastly greater flexibility for turning and milling in the lathe. My view is that ELS falls far short of two axis CNC for my needs but then- like everything else on this forum- it is a matter of personal taste.

 

Billy.

[Gone AwayParticipant @goneaway]

Posted by Billy Mills on 22/01/2012 01:15:37:

Many people have used an ELS as a halfway point to CNC conversion. However I would maintain that if you have a lathe in half decent condition it is already very well equipped for screwcutting. If the machine reverses easily then a lift up toolholder makes screwcutting a quick and certain process without the added electronics.

I saw it as an easy way to control feed rate without having to go to all the trouble of swapping change gears on an ML7 (without gearbox) every time I wanted to go from rough cut to finish or back. In addition to not having to set up gears for screwcutting with an incomplete set of change gears.

 

That said, I’ve been working on my ELS for several years and one day (real soon now) I’m going to finish it.

[John Stevenson 1Participant @johnstevenson1]

One point I’d like to make and I don’t have a horse in this race as I have neither of the units described, neither is my daily drive CNC’d or anything like.

 

Some years ago, many in fact , I bought a brand new ML7 from Myford. being young and cash strapped I bought the basic model and drooled over the rest. I always lusted after [a] a screwcutting gearbox and [b ] Judy Williams from down our road.

 

Years later I managed to pick up a clapped out ML7 with hardy worn screwcutting gearbox for not much money. Judy Williams unfortunately always eluded me.

 

So with a big smile on my recent acquisition I transposed the box onto my lathe. As I was also doing some very odd part I also needed the metric conversion. At this time the only ones available were genuine Myford. The Indian cow dung pattern clones had not arrived here at this time. So much lighter in the wallet I was setup.

Oh the joy, a quick flick of some levers and all was set. A quick flick of reversing a gear and fine feed was available.

 

Then came the need to do a metric thread.

 

What used to be a 5 minute job of swapping some gears on the old ML7 now became15 minutes changing ALL the gears and the banjo, plus I had now lost the fine feed until it was all put back.

 

To be honest it turned out to be a total disappointment [ on a par with Judy Williams ] that I never really got over.

 

If you do lots of different threads and a jobbing shop really shows this up [ Must check if the all metric small TOS can cut 11 1/2 tpi for some unions next week ? ] then one of these units would be ideal.

 

Even me with a good grasp of CNC prefer a hand held unit that having to go full CNC.

I have a division master and to be honest this is in virtually weekly use and I’d be dead in the water without it.

I have seriously looked at the Putnam unit but held off as I knew Tony had one. Fitting one to the small TOS even with the one pulse per rev I feel I’d not have the problems Tony had given the large 3HP motor and geared head.

 

At the moment I keep a CVA lathe for imperial threads and the TOS for metric. The CVA is down at the moment having new spindle bearings but perhaps a Putnam would allow me to dispose of the CVA and do all the threading on the TOS.

 

This is just my personal take on it.

[KWILParticipant @kwil]

I look forward to Alan (cncyormyford) actually marketing his device await the price shock.

 

K

[Alan JacksonParticipant @alanjackson47790]

On my Stepperhead lathe I use TurboCNC with one pulse per rev, this is a basic DOS program. It can cut G33 and G76 screw cutting modes very well. It is better to choose the low belt drive mode (Back gear mode) to ensure speed stability and adequate torque availability as this ensures an accurate thread pitch. I can also use it in a half CNC manner by setting G33 in MDI mode (Manual Data Imput) for screw cutting and using the retractable top slide set at 27 or 30 degrees  and use the top slide to set the cut depth, manually retract the tool then change the G33 Z parameter to plus from minus ( or vice versa) to return the threading tool back for the start of a new cut, return the topslide back to its previous position, add a new depth of cut, reset the G33 Z parameter back to its previous setting and start the new cut by pressing the return button on the computer, and do  this as many times as is required to complete the screw thread. While this may sound long winded it is actually a quick and simple process when observed. with no watching the thread dial as on a manual lathe to feed in the tool at the right moment. The big advantage is that there is no set up required to ensure the thread is cut to the required depth before starting the process, which suits one off operations.

Alan

Edited By Alan Jackson on 22/01/2012 12:39:24

Edited By Alan Jackson on 22/01/2012 12:49:27

Edited By Alan Jackson on 22/01/2012 12:51:29

Edited By Alan Jackson on 22/01/2012 12:53:31

Edited By Alan Jackson on 22/01/2012 12:56:00

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by Sid Herbage on 22/01/2012 02:03:42:

I saw it as an easy way to control feed rate without having to go to all the trouble of swapping change gears on an ML7 (without gearbox) every time I wanted to go from rough cut to finish or back. In addition to not having to set up gears for screwcutting with an incomplete set of change gears.

 

That said, I’ve been working on my ELS for several years and one day (real soon now) I’m going to finish it.

That is one of the great attractions, in my view. John S’s post about the difficulties of using an ML7 with screwcutting box to do metric, imperial, and finefeeds is exactly the experience I had with my ML7 (which incidentally is the machine John was talking about – I bought it off him a few years back). If you add BA, …etc. to the mix then it just gets worse – not to mention the gyrations you get into if you are trying to cut a worm thread to engage with a DP spur gear. With either of these controllers, you can define any finefeed you like, and any thread pitch you like, just by pushing a few buttons. The ML-7 plus gearbox was a brilliant setup if all you ever wanted to do was Imperial threads; for anything else you are actually better off without it & just use the change wheels.

 

Regards,

Tony

[VersabossParticipant @versaboss]

John Stevenson wrote:

> I always lusted after [a] a screwcutting gearbox and [b ] Judy Williams from down our road.

John, I have many pictures of screwcutting gearboxes, but to better understand your disappointment, do you happen to have a picture of Judy Williams somewhere, which you could post here?

(well I found a Judith W., but you come too late in that case) :

http://www.judith-williams.at/ueber-judith.html

Greetings, Hansrudolf

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by KWIL on 22/01/2012 11:47:51:

I look forward to Alan (cncyormyford) actually marketing his device await the price shock.

 

K

The price shock is actually pretty mild…

 

EMC2 is free, as is the Linux operating system that it runs under, and both will run happily in a clapped out PC that isn’t good enough to run Windows any more, as long as it has a parallel port – if not, they can be bought as add-on cards for a tenner.

 

You can build yourself a shaft encoder with (say) 60 slots at the periphery of an ally disk (one of the platters from an old hard drive is ideal) and a couple of optical sensors to give you a quadrature encoder. Plus a third sensor & slot to give the index pulse. Parts cost significantly less than a tenner.

 

Yes, you will need a couple of stepper motors and stepper drivers, a PSU, and probably a breakout board. Parts cost £200-300.

 

So all in, a fraction of the cost of a Myford screwcutting box and Metric conversion set, which as I have pointed out above, isn’t nearly as flexible.

 

Of course, all of the above means a fair amount of time & messing with soldering irons, but that is part of the fun.

 

Regards,

Tony

Edited By Tony Jeffree on 22/01/2012 13:07:24

[blowlampParticipant @blowlamp]

Hansrudolf.

 

If it’s the Judy Williams I’m thinking of, then just about everyone on this forum will have a picture of her – or some other memory, somewhere

 

 

Martin.

Edited By blowlamp on 22/01/2012 13:26:25

[mike TParticipant @miket56243]

Hello Tony

 

The idea of EMC2 software running on an old PC connected to the existing shaft encoder of my old EMCO Compact 5 CNC would appear to be a perfect answer to updating this old machine.

The EMC2 website looks so intimidating with so much to learn than I have days left on this planet. Does anyone have hands on experience of making a lathe controller with EMC2? Can anyone, perhaps Alan (cncyormyford) give a simple tutorial about how to use EMC2 as a lathe controller?

 

Mike

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by mike T on 25/01/2012 18:59:14:

Hello Tony

 

The idea of EMC2 software running on an old PC connected to the existing shaft encoder of my old EMCO Compact 5 CNC would appear to be a perfect answer to updating this old machine.

The EMC2 website looks so intimidating with so much to learn than I have days left on this planet. Does anyone have hands on experience of making a lathe controller with EMC2? Can anyone, perhaps Alan (cncyormyford) give a simple tutorial about how to use EMC2 as a lathe controller?

 

Hi Mike –

 

I haven’t played with EMC yet, I’m afraid. It is on the list…may be some while though.

 

Regards,

Tony

[Gone AwayParticipant @goneaway]

Posted by mike T on 25/01/2012 18:59:14:Can anyone, perhaps Alan (cncyormyford) give a simple tutorial about how to use EMC2 as a lathe controller?

 

 

Perhaps MEW could run an article on it.

 

Cor … wouldn’t that put the cat among the pigeons

 

 

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by Sid Herbage on 25/01/2012 22:49:49:

Posted by mike T on 25/01/2012 18:59:14:Can anyone, perhaps Alan (cncyormyford) give a simple tutorial about how to use EMC2 as a lathe controller?

 

 

Perhaps MEW could run an article on it.

 

Cor … wouldn’t that put the cat among the pigeons

 

 

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