Extruder changes direction in middle of Print

Hi this is a problem I have benn dealing with for more that 5 months.

My extruder changes direction in one of the machines, connected to a MAC OS, in the middle of print.
I am using Makerbot motherboard and stepper controllers,
I have another achine connected to Windows and this doesn;t happen.

I think it might me the software on mac, I a using replicatorG 040, with the latest Skeinforge.

I think is something on skeinforge

I am printing a lower carriage for a mendel now, and on 40 minutes the extruder changes direction of extrusion,
and then after 3 minutes it goes back to normal, correct direction of extrusion. The sae thing will happen at 1.20
minutes, so every 40 minutes. For another piece it changes de value, but still constant within the same piece.

Thanks to everyone!

I hope you can help me,

Rep Rap Argentina. José

Does gcode reflects the changes of direction? Are you with relative or absolute positioning (G90 or G91 at the beginning of gcode —I'am not quite shure this plays with extrusion too)? If you are with Absolute Extrusion Distance in Skeinforge's Dimension plugin, there is a parameter which resets E value: Maximum E Value before Reset.

Edited 1 time(s). Last edit at 05/18/2013 09:47AM by François Delègue.

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François

Let's be clear on what you mean here. When you say the extruder reverses for 3 minutes, that means to me that it starts retracting filament for 3 minutes. After retracting for this long, I don't see how it ever recovers because by the the filament would have come completely out of the extruder.

Hi thanks for the responses I am with ReplicatorG and skeinforge.
I am using Dimension, active, absolute extrusion distance, and the parameter before it resets E on 91234.0.

I tried changing this and you think it will change the problem? I tried it before but if it gets to high it also does the reversing effect.

Jbernardis, what happens, in only 1 of my machines, cause the one that uses Windows doesn´t have this problem which is weird. Is that after 40 minutes of printing for example, it just changes direction for 3 minutes. What I do is Pause is, change the wiring of the motor, and keep on printing, and then change it again when it comes back to normal (cause it does) this i very strange and it is happening in 1 printer!

Thanks for the help, that E value do you recommend? Should I put relative extrusion distance?

Jsé.