Thread: First Proper CNC Router
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05-12-2019 #101
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05-12-2019 #102
This vibration could be causing resonance which will affect the performance.
However, at 5Mtr/min your close to reaching the limit and other factors will come into play so resonance could be clipping your wings a little.
Also depending on the controller then you might be better off dropping the micro-stepping. When reaching limits the controller and quality of pulses starts to play its part.
With 68V and digital drives on a machine with decent rails, aligned and set up correctly with average gantry weight of 30-50kg then I'd expect to top out around 7mtr/min with 5mm pitch. I would tune to run at 5mtr/min.
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06-12-2019 #103
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07-12-2019 #104An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.
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09-12-2019 #105
Had an experiment with micro-stepping today. Increasing micro-stepping reduced noise, and increased the speed before it started skipping steps.
Im using GRBL for testing, which has a limit of 30kHz, so 1/8 is about as high as I can go and still achieve a sensible speed. Any higher and the Arduino crashes.
What micro-stepping settings do others tend to use when running Mach 3 or similar from a parallel port?
The drivers go up to a whopping 1/256!
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09-12-2019 #106
A lot depends on the stepper drivers - many max out around 100kHz-200kHz.
My recent tinkering are with a lathe conversion and I'm settled at 8x, though I'm re-using modified drivers that will take 250kHz
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09-12-2019 #107
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11-12-2019 #108
I'm running Nema 23 / 3Nm steppers driving 2005 ballscrews up to 1000 RPM via 1-1 belt drive giving 5m/min rapids. I use x8 microsteps and it all works fine. General opinion is that somewhere around x8 is the sweet spot between smoother, quieter, motion and losing torque (which happens as you wind up the microsteps). I wouldn't exactly say that my machine purrs but it isn't a bag of nails either!
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11-12-2019 #109
Pointless because your motors cannot resolve that low and it just stresses the pulse engine, Also if I'm reading correctly and you are using an Arduino then I'm not sure it can output pulses at this rating.? . . . But i don't know much about them so could be wrong.
The main reason to up the MS is to give smoother running motor but there is, as always a cost, much past 16x is waste and just stresses out the controller and wastes torque.
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17-12-2019 #110
The max frequency for a GRBL on an arduino is 30kHz, which effectively limits me to 1/8 anyway.
I just tried running a motor off the machine, with zero load, and it's 50:50 if it will run at 900rpm, which is only equivalent to 4.5m/min. I can feel the motor start to vibrate as it accelerates up to speed.
Going to try tidying up the wiring to see if that helps. Got twisted pair for the control side. For the motor side, this might be a silly question, should I run all 8 wires all the way to the driver and connect the pairs there, or join the pairs close to the motor and just run 4 wires from there. For the purpose of testing I'm not using shielded cables at the moment, would that impact motor performance at all?Last edited by diycnc; 17-12-2019 at 11:45 PM.
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