reasons why a stepper maybe missing steps

[eloid]

hello,

Im try to understand why my stepper motor on z axis may be lossing steps..
I dont think it any thing mechanical with the z axis every ting is tight and there no play visable in z axis set up...


here are some of my thought...

1. Motor does not finish the acceleration ramp.
2. The motor is operating at the limit of its ability and stalls because it develops after the acceleration much more torque than needed. This causes vibrations the motor may not be able to damp.

my suspicions are i will have maybe retune my z axis but looking for a way to confirm my suspicions, I noticed it drifting after 8000 lines of gcode..

Is there a way measure / confirm the missing steps?

[dertsap]

Originally Posted by eloid hello, Is there a way measure / confirm the missing steps?

try slowing the accel/decel and velocity then try doing the same cuts ,if that helps then thats the problem

[Miguel-]

I had problems with steppers loosing steps and it was caused by mechanical harmonic vibration. My setup was steppers@fullstep and ballscrews. Power was delivered by toothed belts (or whatever its called). I got the machine going full speed OK but when i started doing some cutting -it lost steps. It took a while to find the problem and it was caused by "hard" stepping at full steps, screw inertia and drive belts tension. I got it working good by changing the stepper drivers to ones that do a microstepping. Also the noice was dampened quite much.

Did the spindle got lowered when you lost steps? When you setup the speeds the spindle doesnt have any forces leaning to it. But when you mill sideways and stop (ofcourse depending on mechanics and material being milled) it might have some forces leaning to it and it might be a bit "sluggish" with getting up when having these sideway forces. I had this problem when I milled some aluminium at first time (my setup wasnt very rigid at time) and I lost a bit there...

[pminmo]

It can be a software setup issue, what software? Depending on software, if you use a low true step pulse, and it's really the opposite, you will periodically miss a step. If you don't have a step pulse wide enough, you can periodically miss a step. Usually missed steps due to resonance or motor power issues are more than a step here or there. 8000 lines of code with a missed step I'd bet on inverted step pulse.

[cgosnell]

I agree with pminmo. I had just this problem with my machine when building. I chalked it up to long lengths of unshielded wires, etc...

Also, the simple drives (using threaded rod, etc...) would have a drive 'max' that seemed to coincide with a harmonic of the steppers, etc... I ended up putting a 'rattle' on the end of the axis drive rod. This was a simple disk that had 'deer' slugs type of shot balls in larger bored holes loosely placed radially in the disk and captured. I wasn't the first to think of this, I'm sure you can find the references using google. My max accel and top speed when up quite a bit after this mod.

BTW, are you losing Z steps when going up (against gravity) or down (with gravity)? Try setting the axis accel very slow and ramping up. Lastly run higher voltage (if possible) to the stepper motors.