Blob of filament extruded when resuming from a pause...
I'm trying to understand why I am getting this behavior: When I resume from pausing a print on my i3Mk3 to switch to a new roll of filament, the printer moves back to the original location where it paused, then extrudes a big blob of filament before proceding to try and continue the print. This basically ruins the print. How can I prevent this?
Photo below shows the blob.
Also, this is my first post here, so please let me know if there's a better forum for me to post this question. Thanks ahead of time!
RE: Blob of filament extruded when resuming from a pause...
Yes, this is probably as good of a sub-forum as anything.
Does this blob appear only after the print is actively resumed, or is it present after you pause/unload/load?
I always make it a habit to brush off the nozzle area when doing any pause/resume operation for anything.
RE: Blob of filament extruded when resuming from a pause...
@jsw - Here's the order of operations that I did, maybe I'm doing something wrong?
1. Print is going fine, but see that the filament is about to run out. I get another roll ready.
2. I hit the "Pause" option. The printer stops printing, raises the Z-axis up a little, moves the head completely to the left, and moves the print bed forward.
3. I choose the "Unload Filament" option, the correct temperature for the filament, and it unloads fine.
4. I put the new filament into the top of the extruder and it grabs it and proceeds to extrude a few mm worth just to prime it.
5. I remove the freshly primed string from the nozzle and check to make sure there is no more oozing out. It is not oozing. Nozzle is clean.
6. I hit the "Resume" option. The printer moves the head back to the original position on the print where it was when I paused.
7. EVIL BLOB APROACHES - The printer nozzle now sits directly on the spot where it was paused, extrudes the Evil Blob of Doom(tm), and then tries to keep moving along with the print. But the damage has been done, and the print is now ruined. Also, in the case of the print I showed in the photo, when the head tries to move back over the "blob spot", it knocks the print sideways because it runs into the blob.
And that's the way it happens.
Any ideas?
RE: Blob of filament extruded when resuming from a pause...
That is exactly the way I do a filament change mid print except I use a brass wire brush to clean off the nozzle area right before your step 6.
I have yet to see a blob appear like yours.
I do try to time the filament change so that the pause for changing will be in a non-visible or non-critical section of the print, such as infill.
If this blob situation happened to me, what I would try (and I have not done this, just what I would think might work) would be right before step 6 to go into settings and manually extrude some filament to make sure it was flowing smoothly and consistently after the change, remove the 'worm', and then back off (manually retract) the extruder a bit, then watch the thing very closely upon resume and be ready to pause if a blob started to form.
RE: Blob of filament extruded when resuming from a pause...
@jsw
Thanks JSW. I am bascially doing everything you mentioned except for using a brush and doing the extra manual extrusion afterward. The wierd thing is that this isn't your typical "a blob was left over after the purge" situation. The printer actually moves the head back to the original position and then extrudes the extra blob deliberately before moving off that spot. I don't get it.
I will try to do some more experimentation to see if I can find a process that works, or to better understand why it is extruding that extra blob before resuming movement.
Thanks again for all the assistance JSW.
If anyone else knows what's happening here, please feel free to help out! This hasn't been completely answered yet. 😥
RE: Blob of filament extruded when resuming from a pause...
The printer actually moves the head back to the original position and then extrudes the extra blob deliberately before moving off that spot. I don't get it.
I have never seen that behavior. Hopefully someone else will give some insight to what is going on.
RE: Blob of filament extruded when resuming from a pause...
@jsw
Yeah, it's really strange. I think I'll see if I can set up a camera and capture the whole thing just so people can see what I'm talking about.
Rich
RE: Blob of filament extruded when resuming from a pause...
It could be related to this bug: [BUG] Extra extrusion after filament change #2502
Have a look at my models on Printables.com 😉
RE: Blob of filament extruded when resuming from a pause...
I have the same issue.
Immediately after pausing, I chose preheat, because my nozzle starts to cool, otherwise.
I change the filament, and tell it everything is cool, and then tell it to resume.
But by that point, I have in my hand a 1 filament thick bit of a calibration test print that I reserve for this purpose, and I catch the blob just before the nozzle comes down into position. This is no answer to the problem of the extrusion happening, but it is an answer to the print being ruined.
This thin bit of teat print comes from printing out a full bed area single layer, used to test if the bed is level.
RE: Blob of filament extruded when resuming from a pause...
Moved topic to How Do I Print this. General Discussion is not for problem solving.
RE: Blob of filament extruded when resuming from a pause...
I just use change color for this printer does notice if its the same color. Works for me.
RE: Blob of filament extruded when resuming from a pause...
For me, I set up my filament changes in PrusaSlicer and let it print. Mine does what everyone is mentioning for the unload and reload. Once the reloading is done, I remove the extruded filament from the change. When I click the button to continue, it again extrudes a small length of filament and then moves into position. I have to be careful and grab that small amount before the nozzle positions itself back on the print or else it sticks and messes things up.
RE: Blob of filament extruded when resuming from a pause...
Did you get to fix the situation? This is what’s happening and I have no idea how to fix it 
