Extruder Reverses Filament Prior to Print

I just finished a new delta machine (0.92.8) which is mostly identical to another delta that I have been running successfully for several months (0.92.4).

For the most part the machine works very nicely but when printing from SD the machine heats up like normal and then shortly before reaching temperature the extruder begins to quickly reverse direction and continues for about 30 seconds. After that it goes back forward for about another 30 seconds. If I release the extruder spring it eventually stops, all axis home, and the print then continues normally. 

The first thing I checked was to make the sure g-code was resetting the extruder position to 0 - all good. I am using simplify3D and I tried moving the G92 E0 command to various portions of the start code with no effect.

Is there something basic I could have overlooked?


  • There is a firmware option that could do it

    #define EXT0_WAIT_RETRACT_TEMP 150


    also check eeprom what it is set to. Make sure units is set to 0.

  • I wont be able to verify for a few days but I checked the firmware and that indeed looks like the problem (was set to 2000). I used the previous firmware config.h as a starting point so I'm not sure it got changed during the translation but just glad I know now.

    Thanks for the quick response!

  • Until a few days ago there was a bug in config tool multiplying distance with steps per mm. That has changed in firmware so now you have to set mm. New config tool would correct that. So initally it was a few mm i guess when it was steps not mm.
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