How should I adjust the retraction setting

[medicalmodeller 4]

I have been struggling to print a model of a broken bone. The print kept failing as the filament got stuck. I have discovered that this is due to excessive retraction which in turn is due to the nature of bone! When it was printing, one could hear lots of in and out of the filament and then the filament stopped advancing.

I have now turned off retraction and the model prints through to completion, but with a lot of stringing

As a novice I do not understand all the terms in the expert settings for retraction.

I do not really understand combing - which is by default set to all

I do not really understand the z hop explanation and reference to delta towers

I would appreciate some help!

Thanks

MM

 

[gr5 2,098]

z-hop means it moves up in Z (nozzle above the part and away into the air) while doing non-extruding moves.

combing - This is complicated but basically it describes keeping the nozzle *inside* the currently printed island. An island is an area within a cross section (the current layer). For example if printing a table and you are on the 4 legs there would be 4 islands to print. Back to combing - if you are printing a C shaped island and it needs to move from one tip of the C to the other, if combing is enabled it will go the long way around staying inside the C so that it doesn't make a mess. Of course when moving from island to island combing should make no difference.

Now none of this has anything to do with your problem. If you know how to use wordcount and grep (wc, grep) you can quickly count the G11 commands in your gcode file and see how many retractions you have but more importantly it's how many times the same piece of filament goes back and forth through the feeder. 10X is usually around the limit. To enforce this you can increase "minimal extrusion before retracting". It defaults to .02mm I believe. This means if your retraction distance set on your printer is 4.5mm you can get 4.5mm/.02mm or 225 retractions on each spot of the filament. In practice this is very unlikely even with printing "bone" fragments. Anyway setting this to .45mm should be relatively safe but still get you *some* retractions. Personally moving this value from .02mm to .32mm made a big difference for me recently and reduced total retractions of a 10 hour print from 34,000 to 20,000 (34k retractions X 4.5mm is 153 meters of retractions! for a print that only needed about 7 meters of filament, lol.

Anyway my point is to increase this from .02mm to around .3 or .4mm. Or even .9mm (no more than 5 retractions for each spot of filament).

 

[medicalmodeller 4]

At last, a person with knowledge!

I am not a Linux user and am not familiar with wordcount and grep. Can the wordcount be done starting within Windows?

Would it be too much to ask if you could look at the gcode for me??

My aim in all of this is to get to a reliable methodology for taking CT scans of bones and convert them to 3D prints. I am using 3DSlicer to convert DICOM to STL as it is Open Source. I have printed quite a few fractures now, but this recent one and one a couple of months ago kept failing. I cannot go on to promote the method until it is reliable. I am now hopeful that your suggestion will make a big difference and avoid this kind of failure.

FWIW, here is a model that printed without these retraction issues

Thanks for your input

MM

 

[personal-drones 44]

gr5 thanks for these explanations, very clear and useful (as usual). Medical, funny because I had exactly the same yesterday, with some bones!!! To see the number of retractions drop the gcode file in a browser window, then Ctrl F (find) and you input G11. Will tell you how many matches there are

 

[gr5 2,098]

@personal drones - good tip! Although it didn't work for me in internet explorer or firefox but *did* work in chrome!

@medicalModeler - just change it to .5mm for now ("minimal extrusion before retracting"). That should keep you from grinding the filament.

 

[personal-drones 44]

@gr5 in such a situation, do you think that tuning the other parameter "minimum travel" could be relevant, in addition to the "minimal extrusion before retracting"?

 

[dutchmen 1]

I could be wrong but i don't count any G11 or G10 commands in my gcode.

There is retraction when printing, though.

Cura 15.04

Marlin 1.0.2-1

Having trouble here with filament getting stuck in bowden tube due to retraction / soft filament (Colorfabb) above hot end isolator (UMO).

Edit: I read now it is a Ultigcode thing.... 8)

Edited November 2, 2015 by Guest