Control system for Harrison M250 CNC

[AdrianW]

I've just bought a Harrison M250 that has factory-fitted CNC system, but the control system didn't come with it. As a result I essentially have a lathe fitted with stepper motors, adjustable stop switches and an encoder on the spindle. I know enough about electronics to sort out drivers for the motors etc. but being new to CNC I really don't know where to start with the control system - I gather that Mach3 is a good option for the SW but ideally I want a controller that will use the features of stop switches and the spindle encoder - it would be easy to use just the two motors but it wouldn't be long before I wanted to do something like thread cutting, and as the lathe doesn't have a full set of change wheels I might as well put the money into improving the CNC features.
So, the question is whether anyone can recommend a control system that would work with Mach3 and interface to the stop switches and spindle encoder.
BTW FP on MYCNC, so Hi to all!

[AndyGuid]

Hi Adrian,

Welcome to the forum from down under. Looks like two of the better options for CNC Lathe Software may be:


KmotionCNC
Acorn Centroid

based on what I recall seeing in fairly recent threads which included:

http://www.mycncuk.com/threads/11430-Centroid-Acorn-Controller-Has-anyone-tried-one?p=99159#post99159

http://www.mycncuk.com/threads/11917-Migrating-from-Mach-3?p=102442#post102442

BUT, I'm NOT in the know on this, so please wait for more informed comments . . . . .

Andy

[Clive S]

Hi and welcome to the forum.

First Mach3 will only count one pulse on the spindle it will do thread cutting of a sort but not rigid tapping etc.

You would need some sort of motion control board to do the step making in hardware.

There are better controllers out there. I use a mesa card which is used with linuxcnc (free) but it does take some time to learn it. You can also put mpg's on it to be able to use the lathe manually.

[Chaz]

I've just bought a Harrison M250 that has factory-fitted CNC system, but the control system didn't come with it. As a result I essentially have a lathe fitted with stepper motors, adjustable stop switches and an encoder on the spindle. I know enough about electronics to sort out drivers for the motors etc. but being new to CNC I really don't know where to start with the control system - I gather that Mach3 is a good option for the SW but ideally I want a controller that will use the features of stop switches and the spindle encoder - it would be easy to use just the two motors but it wouldn't be long before I wanted to do something like thread cutting, and as the lathe doesn't have a full set of change wheels I might as well put the money into improving the CNC features.
So, the question is whether anyone can recommend a control system that would work with Mach3 and interface to the stop switches and spindle encoder.
BTW FP on MYCNC, so Hi to all!

Ive just installed Centroid Acorn on a Harrison M300. I'd never look at Mach 3 again, not the same league.

[m_c]

It all depends on how much functionality you want to add.

If you're happy with on screen jogging, and no fancy tool changer, Centroid Acorn will achieve that. If you want to add an MPG for jogging, then the Acorn is out (it only supports a single encoder input, and has limited inputs and outputs).
If you want more functionality, then a Dynomotion KFlop will give it, but it's not as easy a system to implement.

Mach is still an option, but being realistic for a lathe, you'd either have to ditch the spindle encoder and go single slot, or buy a motion controller that does support encoder threading with Mach. IIRC only the full fat CS-labs controllers with an additional MPG module support it, or a KFlop can work with encoders and Mach3. Some of the Galil controllers probably also support it, but I'm not sure on how well they work with Mach.

I think the CNC Drive UC controllers can support multi-slot threading, but not a full encoder. They also have their own control software, UCCNC, but I'm not sure how much support it has for lathes.
Out with that, you're into a bunch of controllers that can only support single slot threading, or controllers with no threading support. The best guesses I've seen for the number of turn/lathes users in the hobbyist/retrofit market, have all been less than 10%, so there just isn't the same level of support compared with mills/routers.

LinuxCNC with a Mesa card is another option.

Off course, the other option is a standalone controller.

It all comes down to how much money you're willing to spend, and what functionality you'd like.

[Chaz]

It all depends on how much functionality you want to add.

If you're happy with on screen jogging, and no fancy tool changer, Centroid Acorn will achieve that. If you want to add an MPG for jogging, then the Acorn is out (it only supports a single encoder input, and has limited inputs and outputs).
If you want more functionality, then a Dynomotion KFlop will give it, but it's not as easy a system to implement.

Mach is still an option, but being realistic for a lathe, you'd either have to ditch the spindle encoder and go single slot, or buy a motion controller that does support encoder threading with Mach. IIRC only the full fat CS-labs controllers with an additional MPG module support it, or a KFlop can work with encoders and Mach3. Some of the Galil controllers probably also support it, but I'm not sure on how well they work with Mach.

I think the CNC Drive UC controllers can support multi-slot threading, but not a full encoder. They also have their own control software, UCCNC, but I'm not sure how much support it has for lathes.
Out with that, you're into a bunch of controllers that can only support single slot threading, or controllers with no threading support. The best guesses I've seen for the number of turn/lathes users in the hobbyist/retrofit market, have all been less than 10%, so there just isn't the same level of support compared with mills/routers.

LinuxCNC with a Mesa card is another option.

Off course, the other option is a standalone controller.

It all comes down to how much money you're willing to spend, and what functionality you'd like.

On the iPad so quick response from me. Centroid now has an integrated MPG option, 240 usd or so, well regarded. You can also now use something like a shuttle controller as a supported interface.

[AdrianW]

Ive just installed Centroid Acorn on a Harrison M300. I'd never look at Mach 3 again, not the same league.
Thanks for the recommendation - the Centroid forum seems pretty good so it looks like I'm going to be looking for a decent spindle encoder (it's got an optical HP one that's way under the minimum spec.) and also a VFD that's compatible with the Acorn - if you have any suggestions for one that's not silly money I'd be very grateful. I'm liking the idea that I might be able to do rigid tapping!

[Chaz]

Thanks for the recommendation - the Centroid forum seems pretty good so it looks like I'm going to be looking for a decent spindle encoder (it's got an optical HP one that's way under the minimum spec.) and also a VFD that's compatible with the Acorn - if you have any suggestions for one that's not silly money I'd be very grateful. I'm liking the idea that I might be able to do rigid tapping!

Just get a cheap and cheerful Hyangyung one on Ebay. £100 ish and sorted. There is a guy on ebay, near me, selling good quality encoders for circa £45.

[AdrianW]

Just get a cheap and cheerful Hyangyung one on Ebay. £100 ish and sorted. There is a guy on ebay, near me, selling good quality encoders for circa £45.
Cheers - those VFDs look like great value. Do you have a link for the guy selling encoders? The minimum recommended spec is 8000p/r (seems excessive?) and even the 2000p/r ones I've found are in the hundreds of quid.

[m_c]

On the iPad so quick response from me. Centroid now has an integrated MPG option, 240 usd or so, well regarded. You can also now use something like a shuttle controller as a supported interface.

I did have a look last night after I posted to see what they've been up to, and noticed that, but $240 for a XHC pendant you can get on Aliexpress for $99 does seem a bit steep.

Cheap and cheerful option for KMotionCNC is a gamepad. Quite a few people use wireless Xbox controllers.

[m_c]

Cheers - those VFDs look like great value. Do you have a link for the guy selling encoders? The minimum recommended spec is 8000p/r (seems excessive?) and even the 2000p/r ones I've found are in the hundreds of quid.

What's currently fitted to drive the spindle?
Any VFD should be useable with. Only issue would be if the spindle has a DC motor, and a basic non-isolated KBIC style speed controller.

Encoder wise, you need to differentiate between counts/edges per revolution, and pulses/lines per revolution. The 8000 spec will mean counts per revolution, which translates to a 2000 ppr/lines per revolution.
What you're looking for is an "incremental rotary encoder" with a minimum of 2000 ppr/lines, however I'm not sure if the Acorn requires single ended, or differential output (a differential output encoder can be used to drive single ended inputs, but a single ended output encoder would need a differential driver to drive differential inputs). They can be had on eBay for under £40, although you may need to do a bit digging into specs to ensure they do meet the required minimum spec.

[Chaz]

Cheers - those VFDs look like great value. Do you have a link for the guy selling encoders? The minimum recommended spec is 8000p/r (seems excessive?) and even the 2000p/r ones I've found are in the hundreds of quid.

https://www.ebay.co.uk/itm/Hengstler-Rotary-Encoder-2914383-to-fit-12mm-diameter-shaft/113244291277?epid=1449344898&hash=item1a5de2c0cd:g:loEAAOSwySlaJSLx

[Chaz]

I did have a look last night after I posted to see what they've been up to, and noticed that, but $240 for a XHC pendant you can get on Aliexpress for $99 does seem a bit steep.

Cheap and cheerful option for KMotionCNC is a gamepad. Quite a few people use wireless Xbox controllers.

Agreed, there is a markup however they have done all the integration bits to make it work reliably. Ive seen a gamepad being used for the Acorn system too, there was / is a Harrison 300 lathe on ebay with Acorn running with an xbox type controller.

Also, they are about to launch a 16 in / 16 out add on board, lack of inputs and outputs has not helped.

[m_c]

https://www.ebay.co.uk/itm/Hengstler-Rotary-Encoder-2914383-to-fit-12mm-diameter-shaft/113244291277?epid=1449344898&hash=item1a5de2c0cd:g:loEAAOSwySlaJSLx

The potential problem with that, is it's a hollow shaft encoder, which aren't as easy to mount/drive.
Something like this would also work - https://www.ebay.co.uk/itm/1-pc-New-Omron-2000P-Incremental-Rotary-Encoder-2000p-r-6mm-Shaft-5-24vdc/302726959462?epid=2024539084&hash=item467beed166:g:xqoAAOSwImRYIVLB
But that's from China.

It really depends on what the existing setup is, whether it can be adapted, or if a complete new setup is needed. A photo of the existing setup would be good.

Agreed, there is a markup however they have done all the integration bits to make it work reliably. Ive seen a gamepad being used for the Acorn system too, there was / is a Harrison 300 lathe on ebay with Acorn running with an xbox type controller.

Also, they are about to launch a 16 in / 16 out add on board, lack of inputs and outputs has not helped.

A lathe using a gamepad controller fills me with dread for some reason!
Probably because I know how much a damage a crash on a lathe can do, where as at least on a router/mill, the biggest damage is likely to be a broken cutter.

I noticed the IO expansion as well. It's interesting they're having to rely on ethernet though. I would of thought using the i2c or UART ports on the BeagleBone would of been an easier option.

[Chaz]

The potential problem with that, is it's a hollow shaft encoder, which aren't as easy to mount/drive.
Something like this would also work - https://www.ebay.co.uk/itm/1-pc-New-Omron-2000P-Incremental-Rotary-Encoder-2000p-r-6mm-Shaft-5-24vdc/302726959462?epid=2024539084&hash=item467beed166:g:xqoAAOSwImRYIVLB
But that's from China.

It really depends on what the existing setup is, whether it can be adapted, or if a complete new setup is needed. A photo of the existing setup would be good.


A lathe using a gamepad controller fills me with dread for some reason!
Probably because I know how much a damage a crash on a lathe can do, where as at least on a router/mill, the biggest damage is likely to be a broken cutter.

I noticed the IO expansion as well. It's interesting they're having to rely on ethernet though. I would of thought using the i2c or UART ports on the BeagleBone would of been an easier option.

Agreed, he often sells the shaft versions too. I bought a hollow one and struggled but had to be done.

[m_c]

I forgot to mention, British Encoder (www.encoder.co.uk) are a UK manufacturer/supplier, and are helpful. Not the cheapest option, but a direct drop in replacement for my Denford Cyclone was about £200.
Zapp Automation also supply some encoders, and Gary (who occasionally frequents here) is very helpful.

Other option is US Digital, where you can pick disc/reader head options to suit your application.

[AdrianW]

https://www.ebay.co.uk/itm/Hengstler-Rotary-Encoder-2914383-to-fit-12mm-diameter-shaft/113244291277?epid=1449344898&hash=item1a5de2c0cd:g:loEAAOSwySlaJSLx

I was looking at that earlier - the listing isn't very helpful as it only quotes the P/N and not the code that gives the spec - zooming in on the photo it looks like it's a D/500 which from the datasheets I've seen give it a 500 counts per rev, which is well under the minimum spec. for the Acorn.

I checked the resolution a 2000 count encoder would give assuming a workpiece of 250mm diameter, and it's about 0.4mm, so having 2000 as a minimum spec. doesn't seem that unreasonable.

[AdrianW]

Here's a photo of what's on there now - it's an HP HEDS-5310 - I'm pretty sure this range doesn't go over 512 counts/rev so it's well under the minimum. As you can see space it tight - I'll probably have to make a new bearing assembly to allow anything bigger to fit in. For clarity, the encoder is the smaller black housing up against the gearbox. The larger black cylinder next to the pulley is a bearing housing that's bolted to the mounting bracket.
24867

[m_c]

If you check the RS part number for that encoder on RS, it is only a 500 ppr encoder.
I've just tried finding an official spec for suitable encoders, and although I've found it has to be a 5V differential output encoder, all they say is they recommend 2000ppr, not what the actual minimum or maximum possible is.

Chaz, what ppr is your encoder?
And do you know what limits they put on the appropriate setting in the software?


2000 is high for a spindle encoder on a controller aimed more at the hobby/light industrial end of the market. I've got an old mill that has a 200 line spindle encoder, and it would of been able to rigid tap using it's original controller, which is far more demanding on accuracy than single point threading on a lathe.
For a lathe, even a 50 line encoder would be more than adequate for most reasonable sized threads. I can guess why Centroid recommend such a high count, but that's just because I'm a bit of a geek.

If you're existing encoder is differential output with all the required outputs (A,B, Z, plus their compliments - should have at least an 8 core cable if it is), I'd be inclined to wire it in and try it. Worst case you have to change it, best case you get a functioning spindle encoder that does the job without having to change anything.

[m_c]

Actually, just found the datasheet for the HEDS encoder, and they were only available in single ended output.
Probably best to remove it, measure up the dimensions and see what you can find in a similar size, as space looks at a bit of premium. Plus I'd guess by the setup, and the datasheet, it's a hollow shaft encoder.

US Digital would probably be the option involving the least amount of modifying. Something like an E5 or E6 depending on shaft size - https://www.usdigital.com/products/encoders/incremental/rotary

[Chaz]

If you check the RS part number for that encoder on RS, it is only a 500 ppr encoder.
I've just tried finding an official spec for suitable encoders, and although I've found it has to be a 5V differential output encoder, all they say is they recommend 2000ppr, not what the actual minimum or maximum possible is.

Chaz, what ppr is your encoder?
And do you know what limits they put on the appropriate setting in the software?


2000 is high for a spindle encoder on a controller aimed more at the hobby/light industrial end of the market. I've got an old mill that has a 200 line spindle encoder, and it would of been able to rigid tap using it's original controller, which is far more demanding on accuracy than single point threading on a lathe.
For a lathe, even a 50 line encoder would be more than adequate for most reasonable sized threads. I can guess why Centroid recommend such a high count, but that's just because I'm a bit of a geek.

If you're existing encoder is differential output with all the required outputs (A,B, Z, plus their compliments - should have at least an 8 core cable if it is), I'd be inclined to wire it in and try it. Worst case you have to change it, best case you get a functioning spindle encoder that does the job without having to change anything.

Mine is 8192, so 2048 X 4. i think Acorn can read much higher than that.

[AdrianW]

One question that's been nagging me - I'm using a lot of speculation from a position of relative ignorance so please bear with me!

- On a lathe, the absolute position of the spindle (and I mean absolute in the sense of knowing e.g. where a specific chuck jaw is from one work session is to the next) isn't important. What's important is knowing where the spindle is relative to the first cut that was made on a specific workpiece.

- If the above is correct, then the only need for a Z (index) output on the spindle encoder is for pulse-count verification.

- If both the above are correct, then there is no reason you couldn't increase the effective pulse count of the encoder by having a different drive ratio to the encoder e.g. having a 1:4 drive would increase a 2000p/r encoder to be 8000p/r of the spindle.

Does this make sense, or am I missing something? I guess you could run into non-linearity problems if one of the pulleys was too small and the belt had any 'set' in it.

[m_c]

It all depends on the controller.
In the Centroid case, as they specify an encoder with an index pulse, I'd guess they are relying on the index pulse to synchronise moves, which if you're not threading, it likely doesn't serve much purpose. Without it, unless the controller continually counts the encoder, the controller wouldn't be able to synchronise for multiple threading passes.
The controller relies on you setting the encoder count in settings, and I would doubt if there is in any verification between the counts and the index pulse. There might be, but it's more likely to just show up as threading moves failing to start due to the lack of index pulse.

If you were to have more than one index pulse per revolution, then it's likely to cause synchronisation problems. If the controller is relying on the index pulse to start a synchronised move, then if there are four index pulses per spindle revolution, odds are not good for success.


I wouldn't worry about non-linearity problems on a lathe spindle. For basic turning, even if the spindle location varies by 10% over a revolution, it's going to have minimal effect on normal thread pitches. Even on a 2mm pitch thread, that's only potentially 0.2mm, which on a 2mm pitch thread, is neither here or there unless you're aiming for some kind of precision fit thread. A generic nut and bolt will likely have more play than 10% of pitch.

[AdrianW]

if there are four index pulses per spindle revolution, odds are not good for success.
Yeah - I had been assuming that the rotations would be counted by a running pulse total i.e. (pulses/pulses per rev) but as you say it's entirely possible that the index is used to reset the position - this could have odd effects!

[m_c]

Yeah - I had been assuming that the rotations would be counted by a running pulse total i.e. (pulses/pulses per rev) but as you say it's entirely possible that the index is used to reset the position - this could have odd effects!

It's something that the designers will know, but they don't always release the information, as it's not something you really need to know for implementation. You just need to know if an index pulse is needed or not.

I know the KFlop continually counts the pulses and you don't need an index pulse, but it has a lot of the internal workings exposed so you can customise exactly what it does. If you don't have an index pulse, it relies on using wherever the encoder count started as the index point for spindle orientation. Even if you do add an index pulse, all it can do is reset the zero point to the index pulse location (or any offset you'd like).
On my lathe, although I have the encoder index wired up, I only ever used it for confirming the encoder count when I was setting things up, it's never been used since.