Control system for Harrison M250 CNC

[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...EAAOSwySlaJSLx

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-...oAAOSwImRYIVLB
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-...oAAOSwImRYIVLB
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.

[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.

[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.

[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.

[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/e...emental/rotary

[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.