Full/Half/Quarter/Eight Step Size?

[pminmo]

For those of you who have a cnc router or mill or other cnc machine that requires torque from their stepper motor. What is you preference on step size?

[PEU]

I use 1/8 step

[joecnc2006]

Does someone have the a simple chart or know what the binifits of each are?

[ESjaavik]

I use 1/10 and 1/20 microstep just because that gives less noise and higher speed.

There is no difference in low speed torque that I can find between 1/4 1/8 or the other steprates using my drives (Phytron). Neither is there any benefit in resolution. When I measure the distance of one microstep, it may be 0 for a couple of steps as the pressure builds, then it catches up on that and a couple more (stick slip).

There is however a difference at medium speeds where the smooth movement of microstepping makes it possible for me to run the drives at a lower current setting without loosing steps. That means again less noise. And potentially cheaper drives. Of course not in my case when I already paid for 12A and adjust it down afterwards. But if I were to convert exactly the same machine again, I would know I can get the same performance with cheaper drives.

[JFettig]

I like 1/10th step for 5tpi screws becuase it gives a perfect .0001" step. For higher tpi screws 1/4 and 1/8 would be my preference.

Jon

[mcmmach]

As a general rule you should use the lowest step rate possible to get the most torque out of your steppers and maintain the resoulution needed (most gantry type routers only need .001 or less, most mills need .0005 unless you are doing super precision work)
Torque drops off rapidly from full step and by the time you reach 1/8 step you are only getting @ 20-25% of your rated torque.
The best solution is to gear your motors thru zero backlash belts and pulleys to use full or half step.
Dean

[ESjaavik]

@mcmmach: What I was trying to express is that microstepping does not improve your resolution much. Unless of course as you indicate if the motors are grossly oversized. You're right in that one should calculate gearing using +- 1/2 step to find your resolution. This beacuse at 100% load, it is in theory just at the point of cogging over to miss a step. In other words 1/2 step away from where you told it to be. As you load it to 101% it will miss a step. (In theory. In practice it can occur at a somewhat lower/higher load). At low speed, microstepping will not change this at all. It will just move the angle at which it misses the step.

Then after determining this resolution, you add microstepping to improve higher speed behaviour. Without microstepping there will be speeds you cannot run because the coarse torque transititions of full/half stepping will excite resonances. Before microstepping they put on weights, fluid dampers and other means to dampen these resonances or move them out to less troublesome frequencies. It was also a common solution to not use speeds in the resonance range. But this is a problem in CNC machines where the motor speeds are related to each other.

Today we use microstepping because it makes gentle transititions when going through the steps. Thus it does not excite the resonances and there is much less tendency to loose steps at speed. It also runs much more quiet for the same reason: the torque is smoothly delivered instead of yanking the shaft each time a step transitition occurs. It's like having 8 cylinders instead of 2 in a combustion engine, they may make the same power but the 8 does it much smoother.

At high speeds the masses smooth out the pulses, so microstepping have it's benefit at low to medium speeds. As also seen in industrial drives: they revert to full stepping at the highest speeds.

So microstepping give you nothing in resolution or low speed (<300step/sec) torque, but a gain in useable torque through the speed range.

[keithorr]

Originally Posted by joe2000che Does someone have the a simple chart or know what the binifits of each are?

I get great resolution using 1/8 step, but the machine itself is not physically capable of maintaining the accuracy 1/8 step provides (backlash, flex).
I get double the ipm switching to 1/4 step and still have a theoretical resolution of .008/inch. Good enough for carving.
Depends a lot on your screw pitch. Fine pitch, use bigger steps, coarse screw, use smaller steps.