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cura problem retracting all the filamant

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hi all


I am a newbie to cura having used some other packages before.  I am using cura 3.5 and before that he 15.02 etc


Im printing an R2D2 for my daughter and as you can imagine some of the parts are quite bit so it is really annoying and a big waste of filament if part way through the print a command or other gets the printer to unload the filament entirely.


it has happened to me before on another print when three times in a row it got to the same point and retracted it all.  to fix that I changed the settings a little (so that it was printing support) and it didn't happen again.


I just happened to be standing next to my printer a couple of minutes ago and it did it again. interestingly once it had stopped unloading it immediately started to load it again and has been printing fine since so I assume it is something do not being relative positioning or something?


any thoughts?  should I try to find the problem in the Gcode and delete that line.






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This is a common problem in Marlin/arduino printers.  It's a data error.  Some of the gcodes are getting bits flipped.  Let me back up.  To get gcodes into the arduino it usually comes from either a USB serial cable or from an SD card.  They often then travel through two ribbon cables to the arduino.  Either the SD card, the ribbon cable, or the USB signal is flakey and bits are getting flipped randomly.


There is a checksum such that if one bit is flipped it will be discovered but the checksum is only 8 bits (256 possible checksums).  When the checksum doesn't match the gcode is resent to the arduino.  But once out of every 256 times the errors add up to the proper checksum and a bad gcode gets through.  This is the problem for you.


So typically a gcode like this:

G1 X50.123 Y23.332 E190.243

can get any random number changed to another.  So if the E190 gets changed to E100 it retracts 90mm and then the next gcode is fine (e.g. E191.111) and it unretracts.  Also you will see things like an X107 change to an X207 (if your printer is that big) and it will move way over by 100mm off to the edge of the printer and then go back and continue.  It leaves this little strings on the outside of the print.  You can usually hear these anomalies while it prints.  Also you can often get the dreaded "out of bounds" or "tried to print outside volume" or something like that.


If you are using SD card the solution is to clean that out.  I had a single hair causing a problem once.  Try taking it apart and cleaning with vacuum or blowing air or toothpicks or qtips with alcohol.  if it's the USB try using a different cable or different computer that might have more oomph to the voltage signals.  Keep microwave ovens and computers and such far from the printer (at least 1 meter).  Where possible.  Repositioning the ribbon cables sometimes helps also.  And/or separating them by a few mm with some kind of non conductive spacer such as blue tape or foam.

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