Single layer offset

Hi,

I am experiencing an odd phenomenon with my Mendel.

Part way through a print (about 75% through) I got a single layer offset in the y axis by about 1mm. The next layer printed properly directly above the first 500 odd layers, as did the remainder.

I have heatsinks and fans on my stepper drivers (in any case I would not expect a slip in one direction followed by an opposite slip of exactly the same amount perfectly timed to coincide with the Z axis increase!)

Does anyone have any suggestions? I could look through the gcode but its a large part so tracking down the exact bit would be difficult, besides, the 3d view in pronterface did not look like there should have been an offset.

Thanks

Andy

This used to happen to me. Be sure your drivers are very well heatsinked, and that the reference voltage on the pots are 0.4V.

Also, do you have acceleration enabled?.... if not, that may be a factor.


-Nick

Thanks for the advice but as I said - stepper drivers are well heatsinked and the symptom of a skipping motor would be an offset from that point on in the print, not a single layer that then returns to normal. Drivers are also set to just less than 0.4V.

What do you mean by the acceleration? I thought all firmwares use some form of acceleration? Therefore I must have it enabled. How does this factor in?

If a single step is missed ANYWHERE in the print, the entire print is offset that much from that point on... that's the disadvantage of steppers, no feedback.

I would say if your drivers are well heatsinked, bump up the reference by .05-.1 (on the axis that skipped) and you should be good.

Most firmwares do do acceleration, but some are not enabled/set correctly so it would be worth looking into what your settings are.

Acceleration helps gradually get the mass moving. If it accelerates too fast, the stepper might not keep up with the driver, resulting in a skipped step.


-Nick

I think you misunderstand my issue - the print is not offset from that point onwards, only a single layer is offset before it returns back to the correct (zero offset) position and builds as normal. So I end up with a piece 750 layers high with one single layer jutting out by 1mm.

I will look at my acceleration, but I would expect that if this was a problem it would happen a lot more often than once in a print (and not correct itself again for the next layer)

Oh wow... yeah i completely misunderstood.

If you reprint the object does it happen consistently? Could you post your gcode?

-Nick