I am new to cnc's and have just completed my first diy cnc. (metric)
I am having a problem with setting the stepper motors up.
My stepper motors are Nema 23, 200 steps per rev
My micro steps settings are 1/8
My lead screw is 1 turn = 2mm
I am getting so confused with the setting a do not know what to put into Mach3
Can someone help me with these settings.
Fairly straightforward once you know how...
Your motors are 200 steps per rev with the drivers set on 1/8th step, this means you have 1600 steps per rev. (200 steps x 8 microsteps).
Lead screw is 2mm for 1 turn, mach3 needs to know how many steps for 1 unit (or 1mm).
So, 1600 steps will turn you leadscrew 1 full turn and in your case move your axis 2mm. Therfore 1600 steps divided by 2mm = 800 steps per unit (1mm).
You could easily get away with setting your boards to 1/4 or 1/2 stepping as set at 1/8th stepping with 2mm pitch leadscrew the accuracy will be 0.00125mm per step, change them to 1/2 stepping then each step will be 0.005mm, the less steps you need the better if you ask me... Of course if you change to 1/2 stepping then the steps per unit will need to change to 200. (400 steps per rev divided by 2mm).
The Following User Says Thank You to HiltonSteve For This Useful Post:
Thanks for that. It now makes sence.
The main bennifit to higher micro stepping is smoother operation at lower speeds but it does come at a cost with higher velocity unless your drives can morph the steps as the RPM's rise. It also makes the parallel port/Mach work harder has it as to deal with more pulses per second.
If you don't want high velocity and the PC/PP are good for it then stick with higher micro steps has you'll get smoother running motors.
Edit: Micro stepping really shouldn't be used or thought off has increasing resolution it's mostly usefull to smoother running motors at low RPM's. Best advice is play around untill you find the sweet spot, not all motor/drives/BOB combo's perform the same so playing around stepping can change a machines performance greatly.!
Edit2: Oh and every time you change the stepping you will need to re-tune the motors for best performance.!
Last edited by JAZZCNC; 13-06-2012 at 03:59 PM.
The Following User Says Thank You to JAZZCNC For This Useful Post:
Kevin don't know If your aware but Mach has a auto step setting feature that is very usefull for fine tuning the steps per.!
To use it you need some form of accurate measuring device, A tape measure hisn't good enough.!! The easist and best way I've found is to use a digital dial gauge.
Fasten the dial gauge to the moving portion of the machine IE Gantry or table if mill but make sure the slide on gauge can still move. Then Open the dial gauge fully and zero, on the next step you will set a distance to travel just less than the dial gauge travel. The gantry or the table will push the slide against the spindle or a stop.
On the settings tab there a button labeled " set steps per unit" just above the reset button, click then select Axis to setup. In the next box enter the distance you want to move, when finished enter the amount shown on dial gauge into the on screen box.! . . Now your axis is set accurately.
The longer the distance you can measure over the more accurate your steps per will be.
I suggest for the first try you enter a small value, if ok which it should be then go again with the max distance you can measure.
In this situation there is no point using the configuration wizard + dial indicator method. All that will achieve is, at best, to make the distance moved more accurate between the points you've measured and also most likely reduce the precision over longer distances. Lets say you use a 10mm travel, 0.01mm resolution dial indicator to 'correct' the error. The indicator will measure to +-0.005mm (approximately), so over a distance of 300mm you've introduced an error of 0.005*300/10=+-0.15mm over that distance. That's far worse than the lead error on a standard C7 grade ballscrew which is 0.05mm in 300mm, and no doubt worse than your average lead-screw.
Even if you use a 300mm digital calliper to get +-0.005mm over 300mm (again approximate - look at the manufacturers tolerances for the calliper) all you've achieved is to find the distance between the two points in the screw you've measured - who knows what variations there are in the pitch between these points? So there's just no point... calculate the number using the method HiltonSteve suggested as that's the best you can expect to get without mapping the whole screw.
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