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Mach4 General Discussion / Re: spindle setup help
« on: May 18, 2018, 10:24:58 PM »
Hi,
if you want really accurate spindle speed Mach can measure it and display it for you.
It requires a sensor attached to the motor shaft that pulses once each revolution, an index pulse. If you connect that to a spare input your controller Mach will measure the time
between pulses and calculate the motor speed. There is a DRO already in most screen sets to display it.
It is not uncommon for the spindle speed to vary somewhat from what you programmed. The error has multiple sources but usually it is non-linearity of the analogue
output of your BoB which is derived from the PWM signal from your controller. There is also a degree of 'slip' between the VFD frequency and the spindle rotational frequency,
its how asynchronous motors work.
Error between what you have programmed and what you actually get are seldom more than 10%. The question I ask is 'does it matter that much'. No doubt any number of people will
jump in and lambast me for my sacrilege...but there you have it. I think in many cases people spend hour upon hour and hundreds of dollars trying to get spindle speed just so
and really gain little.
All the old manual mills, lathes and drills I've used over the years had fixed ratios. I couldn't get exactly the speed I wanted, I used the closest I could get and got on with the job.
Did not having exactly the right ratio stop me....no.....did it make a bad job of the parts I made....no....did I have to make intelligent feed allowances for the speed that could be achieved...
yes.
You will have to decide how much effort you want to make to 'linearise' your spindle speed. Note that Mach4 is not a realtime controller therefore Mach4 cannot in itself close a feedback loop.
Closing a feedback loop requires realtime hardware, ie your controller. I don't believe at this time that your UC100 or in fact any of the UC series has the ability to close a speed loop with
PWM output.
The ESS of Warp9 does have that ability but it is very new and so I can't tell how good a job it does.
The PoKeys 57CNC has the ability and also has PoBlocks board level programming and I suspect would do a good job.
The Hicon of Vital Systems can do it but you have to pay an extra $500-600 to have that feature activated.
Not sure about the PMDX-422, I know it has a good suite of features for lathe threading and would guess that its very possible that it can close a speed loop.
Another possibility to improve spindle speed accuracy without a feedback loop is to use a look up table. You would have to take and record speed measurements.
Then you could construct a table in Mach so that if you programed a speed of 15000 pm say Mach would tweak it to 16300 rpm because your spindle is a little slower than it should be.
It would not be as good as a feedback loop but I imagine you could get to within 5% or so.
Craig
if you want really accurate spindle speed Mach can measure it and display it for you.
It requires a sensor attached to the motor shaft that pulses once each revolution, an index pulse. If you connect that to a spare input your controller Mach will measure the time
between pulses and calculate the motor speed. There is a DRO already in most screen sets to display it.
It is not uncommon for the spindle speed to vary somewhat from what you programmed. The error has multiple sources but usually it is non-linearity of the analogue
output of your BoB which is derived from the PWM signal from your controller. There is also a degree of 'slip' between the VFD frequency and the spindle rotational frequency,
its how asynchronous motors work.
Error between what you have programmed and what you actually get are seldom more than 10%. The question I ask is 'does it matter that much'. No doubt any number of people will
jump in and lambast me for my sacrilege...but there you have it. I think in many cases people spend hour upon hour and hundreds of dollars trying to get spindle speed just so
and really gain little.
All the old manual mills, lathes and drills I've used over the years had fixed ratios. I couldn't get exactly the speed I wanted, I used the closest I could get and got on with the job.
Did not having exactly the right ratio stop me....no.....did it make a bad job of the parts I made....no....did I have to make intelligent feed allowances for the speed that could be achieved...
yes.
You will have to decide how much effort you want to make to 'linearise' your spindle speed. Note that Mach4 is not a realtime controller therefore Mach4 cannot in itself close a feedback loop.
Closing a feedback loop requires realtime hardware, ie your controller. I don't believe at this time that your UC100 or in fact any of the UC series has the ability to close a speed loop with
PWM output.
The ESS of Warp9 does have that ability but it is very new and so I can't tell how good a job it does.
The PoKeys 57CNC has the ability and also has PoBlocks board level programming and I suspect would do a good job.
The Hicon of Vital Systems can do it but you have to pay an extra $500-600 to have that feature activated.
Not sure about the PMDX-422, I know it has a good suite of features for lathe threading and would guess that its very possible that it can close a speed loop.
Another possibility to improve spindle speed accuracy without a feedback loop is to use a look up table. You would have to take and record speed measurements.
Then you could construct a table in Mach so that if you programed a speed of 15000 pm say Mach would tweak it to 16300 rpm because your spindle is a little slower than it should be.
It would not be as good as a feedback loop but I imagine you could get to within 5% or so.
Craig