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I have two otherwise-identical machines (called "Lefty" and "Righty"), so I have a baseline to compare. I am running Marlin 2.0.7.2 on both machines. They are Creality CR-10 printers with BTT SKR e3 Mini v1.2 boards, with Marlin I compiled myself. Both machines are (as far as I know!) running the same exact firmware binary.

When running the same G-code on both printers, Lefty prints fine. But, Righty fires the plastic through -- I need to set the flow rate to 50 % (!) to be correct. I have checked the esteps, both are identical at 415, and this produces 39.5 mm of 40 mm commanded when bumped through 1 mm at a time via the extrusion menu, even on Righty. The XY movement on both machines is 100 % correct.

Volumetric extrusion is disabled in the firmware on both machines, and disabled in the slicer. Both machines are running TMC2209 drivers, set to Spread Spectrum at 650 mA for the extruder. Both machines are set to 1250 accel. The steppers are rated for 1 A, and they are not skipping steps.

The machines were working side-by-side perfectly until I killed Righty's stepper driver with static, and replaced the board. No other hardware was modified.

Why do both machines behave the same with identical G-code, until extrusion moves? Why does Righty try and extrude nearly double what it should be, only during printing, when Lefty works perfectly?

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Annoyingly, this went away with a replacement board. I don't have a better fix.

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For both machines did you compare extruder's (E) steps/mm setting in Marlin and possibly stored in EPROM (so check from the LCD in Configuration>Advanced settings) ?

Also stepper motors ... I believe they are exactly of the same type? There are 1.8 degree and 0.9 degree stepper motors on the market - so exactly doubled flow could be related to rotation. Also the stepper driver board may be configured for mcrostepping (e.g. full steps agains half steps), and this may equally influence the behavior. (I do not have CR-10, so I cannot advice in more details.)

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  • $\begingroup$ The machines have identical hardware -- but more importantly an esteps calibration (measure filament, extrude manually, measure again) is spot-on between both machines. $\endgroup$
    – Bryan Boettcher
    Jan 6 at 19:42
  • $\begingroup$ Thank you. And I believe you have also already excluded microstepping difference, and Marlin configuration is equal for both .I've experienced too weak extruder's stepper setup (voltage tuning), caused skipping steps instead of pushing filament (just one of possible extrusion issues). If your e-steps values are near to nominal characteristics of CR-10 (i.e. afaik close to 100 steps/mm)? If it is two times higher, than maybe Lefty just loses steps? Key question: can you see/test if both extruders rotate with the same speed (e.g. print line) - or one is indeed two times faster (doubles amount)? $\endgroup$
    – octopus8
    Jan 6 at 20:21
  • $\begingroup$ I can't tell if it's specifically double, but Lefty isn't skipping steps. I have seen it skip before and it's a very different behavior with notable sounds. Righty just kicks the extruder gear into high gear when it starts doing extrusion moves. $\endgroup$
    – Bryan Boettcher
    Jan 6 at 20:40
  • $\begingroup$ The pulse for stepper driver have to come from somewere (also btw.: you did not reveal your steps/mm values). There are parameters in Marlin's Configuration_adv.h (HAS_TRINAMIC_CONFIG section) with settings which can influence microstepping values of your drivers, they communicate with stepper driver through pins - but you mentioned the same Marlin and same gcode files. Have you replaced the stepper driver board or the mainboard? Mainboard pin failures would be worst case (and less likely). Maybe still the driver - did you try to exchange stepper drivers between machines? or even extruders? $\endgroup$
    – octopus8
    Jan 7 at 4:06
  • $\begingroup$ I did mention the e-steps value on both machines (415), and the drivers are soldered on with no way to switch them. I had replaced the entire mainboard. It began acting up last night in a different way related to the BLTouch, so I'm just going to replace the whole board and see if that helps. $\endgroup$
    – Bryan Boettcher
    Jan 7 at 15:51

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