Over extrusion after filament change.  

RE: Over extrusion after filament change.

Here are some screen shots of pre and post G1 E5.00000 F1800.00000 commenting.

Circled yellow is with this gcode

M600
G1 X126.879 Y103.121
G1 Z2.625
; G1 E5.00000 F1800.00000 

Circled red is with the gcode untouched

RE: Over extrusion after filament change.

@lazy_pugz

Hi there, I have the same issue with my prints and I am forced to edit the G-Code manually.

Did you manage to find a solution of the issue?

Regards and many thanks in advance for your kind cooperation.

RE: Over extrusion after filament change.

Issue can be reported over on github. Slicer ones here https://github.com/prusa3d/PrusaSlicer/issues?q=is%3Aissue+is%3Aopen+sort%3Aupdated-desc

I believe from reading previous posts and github issues that the action is deliberate.  The correct sequence for user intervention is to not remove the excess from the nozzle but to grip it with a pair of tweezers, then hit the continue button,  then when it extrudes the 5mm to re-prime the extruder pressure before printing when it moves the excess is pulled away as you have it in the tweezers. 

Most seem to be removing the strand, hitting go and then having trouble removing the extra prime bit.  

RE: Over extrusion after filament change.

@neophyl

Thank you for the insight. I will test out the "hold the excess" method and see if it makes a different. Though I do not think it will as when it reprimes the extruder, it does it directly on the print. I will check.

RE: Over extrusion after filament change.

@ivan-k9

No solution found just yet except editing out the repriming gcode. I will have to try out the method mentioned by @neophyl.

RE: Over extrusion after filament change.

One of the thing I wanted to try is adding a wipe tower. I am fairly new to this hobby but I have been hearing a lot about it.

What I expect to happen is the extruder repriming will be done over the wipe tower instead of the print. I just need to figure out how to set one up.

RE: Over extrusion after filament change.

I recall reading that the bit of extrusion was deliberately added to counter a problem of under-extrusion when the print restarts. The thinking was that grabbing a bit of filament with tweezers was preferable to a print with a visible gap.

Pile of unwanted extra filament at a corner

Here is one problem. At each layer, the print started at the same corner of a box and I needed to change filament each layer. Even I used tweezers to remove the over extruded filament, when the nozzle reached the same corner, it seems to have extruded more than it was supposed to. After several layer changes, that corner became an ugly triangle shaped pile of unwanted filament. What can be done to avoid this?

Semi-automatic editing of gcode

On Windows you can use FNR.exe to automate repeated edits such as this - setup a Windows command file with the required edit command and run this on the gcode file - saves manual editing.

RE: Over extrusion after filament change.

Posted by: @neophyl

The correct sequence for user intervention is to not remove the excess from the nozzle but to grip it with a pair of tweezers, then hit the continue button,  then when it extrudes the 5mm to re-prime the extruder pressure before printing when it moves the excess is pulled away as you have it in the tweezers. 

Why is re-priming necessary? It's just been PRIMED.

After all by definition of a filament change, the extruder has just been primed by the new filament. Indeed, unless you see new filament coming out properly, you shouldn't be confirming "yes" that the filament change was successfully completed.

It's hard to believe that the extruder becomes "unprimed" in the second or two between hitting "yes" and the new extrusion. If this were the case, then you would have this problem in spades every time you "paused" a print -- and the extruder does not "re-prime" when it resumes.

RE: Over extrusion after filament change.

You want a definitive answer then go ask a Prusa dev over on github to explain.  Its not my logic, just passing on what I've learned of the 'correct' way to do this with PS.  However I have seen slight gaps in perimeters after a normal pause, at full printing temp filament can leak out in just a few seconds, its what gives stringing on travels after all.  

Take the advice or don't.

RE: Over extrusion after filament change.

I did file it as a "bug" report on github - maybe a compromise could be to make the extrusion length a configurable parameter - anywhere from 0 to however long you want it.

RE: Over extrusion after filament change.

If you are the user 'puterboy' on github who opened an issue about this a couple of hours ago you should be aware that the extra purge of filament is NOT generated by Prusa Slicer but by the printers firmware.  As such putting a bug in there wont get you very far.

Assuming you are using a Prusa Printer (given the forum we are currently in) then it needs to go into the Mk3 forum.  You are in luck though cause there has been an issue there regarding this for years.  https://github.com/prusa3d/Prusa-Firmware/issues/197   opened in 2017.   Several opened in fact. 
Given the age of the Mk3 and limitations on the memory space available in the 8 bit board and that Prusa has gone to a 32 bit board on the new printers then I'd rate the chances of this being altered in the Mk3 firmware in the region of slim to snowballs chance in hell.