What would cause the extruder stepper to skip steps?

Hi All

I am currently trying to dial in my E_STEPS_PER_MM for my extruder to work with gcode cut by Skeinforge 40.

I am using this approach as suggested by araspitfire.

Thing is, I am not getting consistent results when running twice with the same settings... sometimes my extruder motor will skip some steps... one run extruded about 1.5mm too much, whereas the next extruded 4.5mm to little.

I did hear the stepper skip a few times the second run so was wondering what could be causing that.

I am extruding at a feed rate of 50 which the machine seems to cope well enough with.

Any advice would be appreciated.

Cheers

I think you're using Gen 3 electronics. If so, it would skip if the PWM setting for the stepper is too low (either trim pot or your M113 parameter). I've also noticed that it's more likely to skip with PLA if your tip temperature is too low.

Ultimately the root cause is that the torque required to move the filament is greater than the motor can supply at the requested speed. The faster a stepper spins, the less torque it has. to brnrd's point you can reduce the torque by increasing the temperature and thus the flow. Also loo to see if there is added friction from your filament spool.

-Jay