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Extruder steps/mm way off from calculated number

Posted by llamas 
Extruder steps/mm way off from calculated number
July 26, 2017 03:48PM
My extruder steps/mm is requiring a strangely large step rate, and I can't figure out what I'm doing wrong. It's driving me crazy.

For my extruder only, I have to set a steps/mm that is a little over 6X greater than what the calculated value should be. I had to set my steps/mm at ~3400 to drive my 13:43 geared extruder with 1/16 microstepping, when it should have taken ~500. I didn't want to run afoul of the max step rate limitation (though I think it sends all the steps, just chunked out over more time), so I dropped to 1/8 stepping, and saw no change in behavior (albeit with the steps/mm halved). I've swapped driver carriers, checked current limits, verified the motor turns as expected when connected to the driver for another axis (which also served to verify that I was calculating correctly). I swapped out the motor, with no effect. I disengaged the motor from the gears, and counted motor turns; no difference. I ran the operations fast and slow; no difference.

I'm bothered by the fact that the multiple isn't a factor of 8 (though that could be due to error in measurement), since at least that would point to some bits getting shifted someplace. I'm getting a consistent feed at the observationally determined step rate, but the degree of difference makes me think I'm missing something fundamental.

This is with Marlin 1.1.3 on a Mega 2560 with a RAMPS 1.4. No extra features turned on. No LCD. Using Repetier Host (manually sending GCode for some of this).


Re: Extruder steps/mm way off from calculated number
July 27, 2017 01:47AM
Just shooting from the hip, but " a little over 6x" sounds like 2xPi = 6.28 to me??
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