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Electronic Artisans ELS Article

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John Haine28/03/2016 13:31:41
5563 forum posts
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I think that's quite correct, Alan Savelio (cncyourmyford) demonstrated this for Mach3 at the Midlands show IIRC, or at least mentioned it, whereas with Linux CNC it behaves as you would hope. But hey, for many purposes it works! From what some people say Mach3 could never cut a thread in a million years, but I know it can 'cos I have seen it.

I'm not sure what the concern about referencing is? Yes, with CNC you have to reference the tool to the work, but it's no sweat. Once you've done that it knows exactly where to stop the feed and withdraw the tool - if the ELS uses a switch as a stop then you have to reference the work to the stop instead! (As well as the tool to the stop.)

I guess there's a possible issue with Mach3 and larger workpieces where the cutting torque will be larger, but you'd run it slower anyway so there's more drive torque available. And with CNC threading you can always take lots of light cuts, the machine is very patient!

Martin 10028/03/2016 13:40:40
287 forum posts
6 photos
Posted by Ajohnw on 28/03/2016 11:45:39:

That chip with a label on it is almost bound to be a rom which suggests another micro. I also thought that these machines did have controlled spindle speeds. The usual DC speed controller works pretty well, even better with an encoder on it.

If it can work with one pulse per rev

 

On the Boxford TCL 160 (and maybe the 125?) it's more than one pulse per rev (32 minus one missing) and yes it is a processor on that board, a Z80 (or equivalent), can't recall if it's the lathe, the Boxford mill or even both that also have another processor on smaller board with an 8051 (or equivalent) for the turret changer on the lathe or the Z axis on the mill.

 

Boxford TCL 160 head assembly showing encoder disc.

 

 

 

Edited By Martin 100 on 28/03/2016 13:43:26

Lester Caine28/03/2016 13:47:53
25 forum posts
1 photos

I knew when I started this thread there would be some 'controversy' but on the whole the content has been most productive. I am essentially an electronics engineer and making the various components work is not a problem, but I think this thread does show that as of today there is still not a single all encompassing solution to a CNC lathe?

Where I struggle is with the mechanical side of the problem, and while on the whole these days I manage to get the mill working reasonably productively, It still takes a visit next door when something more complex comes up ... or a run over to JS But this thread has started to build on my understanding of the mechanical side ...

John Stevenson28/03/2016 13:51:49
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Posted by Michael Gilligan on 28/03/2016 12:00:30:

I may be in a very small minority here, but:

For my purposes [being to have full set of 'virtual' ratios available], I would like to see all reference to spindle speed taken out of the equation ... i.e. the ELS should work properly when the lathe is being hand-cranked.

This is particularly relevant to short threads, such as found on various optical instruments; but I suggest that it might be the purer starting point in any case.

... I think this demands a high resolution encoder on the headstock spindle.

MichaelG.

.

 

EXACTLY

 

It's about POSITION, not VFD, slip or what ever kludge someone wants to throw into the mix.

 

All this red herring about how to control the speed is unnecessary. It's the same as threading with gears but one gear has 3 broken teeth and the thread jumps. Now everyone is coming up wit ideas how to get round the missing teeth instead of replacing the gear.

 

Speed is irrelevant.

 

Position is KING.

 

Watch this video by the formidable Andy Pugh.

 

**LINK**

Watch the lot if you want but the important bit is 50 seconds in. The bit where he rocks the spindle and the work follows. Note he's not doing a full rev so a one pulse per rev index flag isn't going to do sod all in a case like this.

 

Linux CNC can do this now and has been able to do this for quite a long while. What it isn't able to do is allow a simple setup to do this.

Unfortunately it's down to having a lot of hand holding or adopt the Tormach set of screens which at the moment also need help to set up on a non Tormach machine.

 

Something I have been saying for the whole of this post but it gets hijacked by people who think they know but don't.

 

{EDIT}

 

Thank you Martin for that information about the Z80 chip.

Hardly state of the art these days, so we could do it and now we can't ??

Something seriously wrong.

Edited By John Stevenson on 28/03/2016 13:55:58

JA28/03/2016 14:41:14
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1605 forum posts
83 photos

I run a large bore imperial Myford lathe fitted with an inverter and variable speed control. After reading the article in MEW 240 I thought I could be cutting Metric threads without having to spend over £200 on a set of Metric conversion gears.

Now I am not so sure. Should I even be considering ELS as a cheaper viable option?

JA

Ajohnw28/03/2016 14:50:55
3631 forum posts
160 photos

The use of a Z80 based processor doesn't surprise me John. Wonderful beast especially working with assembler. I has been recognised as probably being the most optimised tiny chunk of silicon on the planet. At least one manufacturer was thinking of adding to other processor chips in the same package. The PIO chips were painful as the data sheets didn't contain sufficient info to get them working. That caused me a serious headache for several days once when looking at incorporating one in an electric vehicle controller.

The big slot in the encoder will be the index. The cheap way. Quadrature encoders can be used to determine the direction of rotation. Their main purpose in life. I suspect that if I was increasing the pulse count with them that I would look carefully at the waveforms first and maybe only double by using the rising edges and maybe even not do that. In use the phasing doesn't always matter that much other than detecting the direction of rotation.

On Linux cnc I did link to something that looked pretty. If people want to have a go I am sure people on the forum would help but do ask them to be gentle and explain that you have no experience at all. If things don't get to running it as some one would like the best place to ask about that would be the disto's forum. Ubuntu in this case. There are various files for organising that sort of thing and desktop icons can be created. This may involve using a text editor. A weird one may be suggested but stick to one that runs on the desktop - not the console ones. Those can do all sorts of weird and wonderful things but use isn't that obvious on some of them once they are running.

John

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Edited By Ajohnw on 28/03/2016 14:53:15

Edited By Ajohnw on 28/03/2016 14:54:53

John Stevenson28/03/2016 15:35:18
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5068 forum posts
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JA,

You don't need to spend £200 on a metric conversion kit for your Myford when you can do it all with just two extra gears at a fraction of the cost and to the same degree if not better accuracy.

PM me if interested as it's going further off this topic.

Bikepete28/03/2016 19:17:04
250 forum posts
34 photos
Posted by Michael Gilligan on 28/03/2016 12:00:30:i.e. the ELS should work properly when the lathe is being hand-cranked.

Here's an example of hand cranking while thread cutting with ELS (looks like cross slide is also stepper controlled, so maybe closer to CNC... but it's still synching with a hand-cranked spindle) . Skip to approx 2:50 to see the hand crank.

Description says "Turning an ACME thread on an old ML7 lathe, by hand. The leadscrew is electronically tied to the spindle using an Arduino Due and stepper motor. There is a 1440 pulse per rev (with Z pulse) digital encoder on the spindle. The code is written so that any pitch can simply be typed in (here it was 3.175mm for an 1/8inch pitch). Imperial and metric threading is simply calculating the required pitch. The lathe backgear cluster has broken teeth, so the motor could not be used to provide a low enough RPM. Motion was done very slowly to ensure the thread cut properly (including repositioning the cutter, which was done automatically). The encoder was salvaged from old medical equipment. All details will be provided at no cost/obligation for anyone interested. CNC rocks."

EDIT - found an even better one:

Edited By Bikepete on 28/03/2016 19:21:05

Michael Gilligan28/03/2016 19:21:59
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23121 forum posts
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Posted by Bikepete on 28/03/2016 19:17:04:
Posted by Michael Gilligan on 28/03/2016 12:00:30:i.e. the ELS should work properly when the lathe is being hand-cranked.

Here's an example of hand cranking while thread cutting with ELS (looks like cross slide is also stepper controlled, so maybe closer to CNC... but it's still synching with a hand-cranked spindle) . Skip to approx 2:50 to see the hand crank.

.

BRILLIANT ... Thank You

You have restored my faith !!

MichaelG.

Muzzer28/03/2016 19:56:30
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2904 forum posts
448 photos

There's another excellent example of a simple ELS system based on an Arduino and an encoder.

There's also a forum linked to in the thread below the vid but it's in Russian. I'm sure with some perseverance it would be possible to reproduce it. Very nicely done.

It appears to be pretty a simple open loop arrangement where the encoder movement is converted to stepper pulses with a ratio that accounts for the leadscrew pitch and the required thread pitch. It's hardly rocket science - nice to see it done in a businesslike manner.

Murray

Michael Gilligan28/03/2016 20:19:07
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23121 forum posts
1360 photos

Thanks, Murray star

We're definitely on the right track.

MichaelG.

.

Edit: via Google Translate

Edited By Michael Gilligan on 28/03/2016 20:44:28

Ajohnw28/03/2016 21:32:16
3631 forum posts
160 photos

The Russian one seems to be using encoders removed from printers with pretty high resolutions.

John

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Michael Gilligan28/03/2016 21:44:56
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23121 forum posts
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1800 lines, processed in x2 mode

3600 pulses per rev.

Mark C28/03/2016 22:29:52
707 forum posts
1 photos

Mmmmmm, resolving down to 6 min's of arc, not exactly single pulse per rev then!

Mark

Ajohnw28/03/2016 23:48:19
3631 forum posts
160 photos

It leaves about 5uSec to do the step update sums not accounting for any jitter at 3000 RPM. Or twice that at 1500rpm. If some one happens to have that perfect Super 7 that can leave a mirror finish even feed rate gets important.

Might be worth remembering that the existing Artisian ELS uses an encoder and from hanging around on the forum not much in the line of complaints that I noticed anyway. It has a fault light too. Seems to be something Mach might not have.

John

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John Stevenson28/03/2016 23:55:45
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5068 forum posts
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Posted by Ajohnw on 28/03/2016 23:48:19:

Might be worth remembering that the existing Artisian ELS uses an encoder and from hanging around on the forum not much in the line of complaints that I noticed anyway. It has a fault light too. Seems to be something Mach might not have.

John

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I was under the impression they all needed an encoder. ??

Come on John, it's about paying attention and reading posts - not post counts wink

Ajohnw29/03/2016 10:43:25
3631 forum posts
160 photos

I had noticed something about posts however there has been a lot of talk concerning one pulse encoders started by your um good self and the els uses more. People reading might think otherwise. To JS in case more posts arrive since reading the latest comment.

I mentioned not being keen on it earlier. The main thing in that area was buttons. I would have preferred BCD switches to set the pitch. At the time I looked I might have worked on the code if it was opensource but it didn't seem to be. The saddle stop it uses is clearly a good idea. I could even use it in conjunction with the micrometer stop on my Boxford however the lathe I had at the time didn't have one, no gearbox either.

John

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Edited By Ajohnw on 29/03/2016 10:43:39

Ian P29/03/2016 11:15:04
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2747 forum posts
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Posted by Ajohnw on 29/03/2016 10:43:25:

I had noticed something about posts however there has been a lot of talk concerning one pulse encoders started by your um good self and the els uses more. People reading might think otherwise. To JS in case more posts arrive since reading the latest comment.

I mentioned not being keen on it earlier. The main thing in that area was buttons. I would have preferred BCD switches to set the pitch. At the time I looked I might have worked on the code if it was opensource but it didn't seem to be. The saddle stop it uses is clearly a good idea. I could even use it in conjunction with the micrometer stop on my Boxford however the lathe I had at the time didn't have one, no gearbox either.

John

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Edited By Ajohnw on 29/03/2016 10:43:39

John

Are you saying that in general ELS systems always have (and always did have) multiline encoders?

Ian P

Lester Caine29/03/2016 11:15:36
25 forum posts
1 photos
Posted by Ajohnw on 29/03/2016 10:43:25:

I had noticed something about posts however there has been a lot of talk concerning one pulse encoders started by your um good self and the els uses more.

The ELS kit uses a single pulse sensor ...

Ajohnw29/03/2016 14:47:37
3631 forum posts
160 photos
Posted by Lester Caine on 29/03/2016 11:15:36:
Posted by Ajohnw on 29/03/2016 10:43:25:

I had noticed something about posts however there has been a lot of talk concerning one pulse encoders started by your um good self and the els uses more.

The ELS kit uses a single pulse sensor ...

laugh Whoops. I had looked at the parts list and noticed a 64p encoder some time ago but hadn't noticed that it was mounted on the PCB.

Bigger laugh - that does make keeping the motor speed as constant as possible relevant to the thread.

I don't think the code is open source which is a pity but can understand why. It would probably get pinched by some other commercially orientated outfit. This often happens even on OS but it just usually annoys people who did the work. Some of the heavier stuff has been done by universities anyway. Actually people would be gob smacked by how much software originated from that source especially off unix. Many now famous names. Mind you a lot have progressed further since that happened.

John

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