Thread: Setting my table up...
Having just got my first CNC table up and running, has anyone got any practical advice on axis tuning in mach3?
i have no idea of what speed or Acceleration G's to Aim for in motor tuning.
its only a small table, I have a work envelope of 650x680mm to play with.
any tips or tricks?
Best advice is start low and work up and only raise one thing at a time, ie Velocity and test the affect.
The way I do it to get a ball park quickly is to double then half.? So say start at 2000mm/min on Velocity and 300s/s Accel.
Test and if ok double Velocity to 4000, test again. if too much then drop to 3000, test again. If ok raise to 3500 and so on.
Do the same with Accel but just be aware you can't have high velocity and high Accel so start with Velocity and find the limit where motors stall then back off 25%. Now do the Accel in same way and you should be in a nice balance. Just tweak from here to get the best performance.
The figures I've quoted are just guide lines and the volts you are running the machine motors/drives and the pitch of the ballscrews etc will determine the starting speed. For instance with only 24-36V and cheap drives on 5mm pitch screw then you may well be near the limits at those starting speeds I quoted.?
Give some info on your setup and will be able to give a better idea of a good starting point.
my machine is all aluminium build, carriage runs on steel rails with bearings.
im using nema 23 motors, 3.1Nm, 4.1A, and a 36v 11A psu.
The drives are all T5 belt, 3:1 reductions on both axes and I'm using 1/8 micro-stepping.
Well you should have high rapid speeds due to high pitch but this obviously depends on pulley sizes thou with 3:1 ratio I can guess at around 25-35mm pitch.
With only 36V then you'll have lower speed and there fore torque from the motors than they are capable of so for this reason I suggest you keep the motor tuning down so the motors are in the lower Rpm range where more torque is available.
Like I mentioned before your problem could come from lack of resolution and motors running too slow causing rough movement.?
There is no problem JAZZCNC, I'm just looking for facts and figures at the moment.
I now have it set for 15,000mm/min and 1300 mm/sec/sec and it's been running a pen over various files repeatedly and has not missed a step yet.
Seems pretty good so far, I think that speed is more than enough for a small machine???
If plasma is limited to say 4500-5000 mm/min, is there any point at all tuning a small machine to 15000-20000mm/min???
My answer is NO absolutley not. High rapid speeds are only any use for A-2-B positional moves like drilling lots of holes or with very large machines. Small machines then IMO it's pointless and can easily get folks into trouble with crashing machine into hard stops etc.
With a small machine your much better off sacrificing Velocity in favor of accelleration and often it brings cycle times down anyway.
Last edited by JAZZCNC; 22-02-2014 at 07:06 PM.
Brilliant, that's exactly what I was thinking too.
the reason I asked is that many threads go on about tuning for high speed, must go this speed etc. but then I realised that plasma itself is limited (at least in home size machines) to speeds of around 750 to 4500mm/min so what the heck is the point of mega speed.
as you said, acceleration seems to be important and on a machine with an envelope of 600x600mm, 20,000mm/min is pretty scary and damaging.
i think I'll limit mine to 5000 max.
If your working with small machine for cutting woods then I'd aim for between 8000 to 10,000mm/min Max Rapids. If cutting mostly Aluminium or hard materials then you won't need much above 3000mm/min and 5000mm/min is a good Rapid speed.
Also Resolution is important so think about that when building a machine.
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