No extrusion after filament change?
I have a new MK3s I built a couple of weeks ago, and for the most part it has been great. So far I have probably close to 100hrs of print time on it with very few issues.
Currently I am working on a print that has many pieces and I am changing filaments quite often between prints to change colors. I have an issue where after changing filaments, when the new print starts I get no extrusion out of the print head and I have to stop the print, raise the head, go to settings, move axis , extruder and then filament will extrude. If I then start the print over, it may or may not work on the second try. Sometimes I have to do this three or four times to get the print to start. Early on I think I remember this happening once, but it is now predictable and doing it every time I change filaments.
When I unload the filament, I do that using the menu. Autoload is grabbing the new filament firmly and it extrudes the old filament color, then the new color as expected. I typically answer no to the first time it asks if the color is now correct, just to get it to extrude a second or even a third run during the autoload. This works fine, the gear is not slipping and the filament stream coming out seems correct.
This is not specific to one print file. The same thing will happen if I run a first layer calibration after a filament change. (I tried this just to verify that it wasn't an issue with the gcode I was using) and it also did it trying to print a benchy from the demo files.
My guess is that I might need to take a look at the extruder itself and I am thinking that maybe my nozzle is partially plugged or something along those line, but rather than just start randomly poking bits in the nozzle I felt it best to ask here about proper procedures and get some other opinions. What doesn't make sense is that I do get extrusion when autoloading the filament and manually running the extruder axis, and then a minute later when starting the print I get nothing.
For the most part I find Prusa manuals to be very helpful, concise and well written. I enjoyed the building process and am really glad I chose to purchase a kit as I have a much better understanding of how everything works and am not intimidated to tear into it if need be.
RE: No extrusion after filament change?
Does the filament change process work fine when you're not doing a multi-color print? When the printer is sitting idle and just testing? If it happens all the time I'm curious if the filament sensor is a bit off.
RE: No extrusion after filament change?
I have the exact same issue. Did you find a solution?
RE: No extrusion after filament change?
it may be a silly question but are you changing the type of filament, i.e from PLA to PETG or vice versa. The temps for these materials are different and I could see putting PETG in at PLA temps causing it to not be able to extrude. Like I said, probably a silly question.
I have two MK3S+ printers with one of them upgraded to MMU2S and I've not seen this kind of issue. The only real issue I've seen remotely like that is with TPU, but that's usually the idler screw being too tight, or trying to print too fast.
RE: No extrusion after filament change?
The first occasion was actually when I was changing PLA to PETG. But it also happened to me when I was changing from PLA to PLA. The strange thing in this is that when you are filling in the new filament it extrudes fine, you can keep selecting the "not printing with the correct color" option and it will keep extruding the new PLA. Then you start the print in the next minute, and it won't extrude at all. I canceled the print, unloaded the filament, opened the bondtech gear part, and tried to see if there is any issue. I pulled the PLA out and retried the whole process and it worked fine. This has happened 2 times already.
RE: No extrusion after filament change?
@tap82
I've only been printing since november so I'm not sure sure based one what you're describing. Hopefully some more experienced folks might have an idea.
RE: No extrusion after filament change?
Good for you! I'm only printing since last week. So might be something very basic thing I'm doing the wrong way.
RE: No extrusion after filament change?
@tap82
Lord knows I made my share of mistakes in the beginning! Wait until you try to print TPU and you end up with it wrapped around your extruder gears!
RE: No extrusion after filament change?
Since the OP is new ...
when choosing to change filament - are you talking about a user initiated filament change, a run-out initiated filament change, or a slicer planned filament change?
On a user initiated filament change - sequence is click knob, select unload filament ... at that point you should be prompted to pick a temperature range - you should select the temp range for the filament you are planning on changing to to help the process. Changing from PLA to PETG and still running the head at 210 to 220 is going to make some PETG such as Prusament PETG unextrudable. It can change and you see the color change, but Prusament needs 240/250 head temp to extrude in a print. That is why if you select prusament in the slicer as the filament type, the resulting GCODE will start the print head at 240, and then after first layer, move to 250.
On a run-out initiated filament change you do not get to select a temp range - so if you decide mid-print during a run-out (either spool or cut filament) the problem you describe can happen if you move from an in-print PLA filament profile to an PETG material - some PETG will extrude at 200 to 210 just fine. But a lot won't - like prusament.
In a color change planned filament change, you will not get to choose a new temperature either. You will need to know what the planned filament change is expecting - since you can have the slicer lay down PLA on the first 20 layers and then switch to PETG - as long as in the layer change in the slicer settings you relate the next color to your planned PETG profile. Switching from PLA to PETG just because you like the color is gong to give you the symptom you describe.
RE: No extrusion after filament change?
Hey Dan,
Thank you for the explanation it makes sense. I've been doing the user-initiated filament change using the knob and unload filament option. Probably selecting the PLA as PLA was in the printer that I unload. That's the logical way how I would think. Unloading a filament? What kind of filament? Anyway, so it unloaded the PLA. Then I loaded the PETG that is automatically loaded without selecting anything, just inserting the filament.
I see the flaw in the process as it's not asking me what kind of filament I'm loading. So I need to make sure the temperature of the hotend is either preheated for the PETG or I select PETG when it's asking what kind of filament I'm unloading. I'm wondering what happens when the machine is cooled down and I randomly insert a filament into the empty extruder.
Anyway, thank you for the help.
RE: No extrusion after filament change?
yeah, I wouldn't even thought about doing pla and petg since I don't believe the two bond particularly well together.
RE: No extrusion after filament change?
@tap82
One more piece of info that will help you. Your question about "i wonder what would happen if I loaded a random filament"...
The printer does not know, nor keep track of the filament you load. It has no way to do that - there isn't some magical digital stripe inside of the filament that would tell it.
The thing that controls what filament temp, speed, cooling, etc is the sliced GCODE file. So if you leave PLA in the printer overnight - the the printer only knows it has some filament. If you then load a PETG print (temp specified in the GCODE you choose to print), it will probably print - but might be very stringy since the temp profile of most PETG is a little too high for PLA. If you have PETG loaded, same gig - in the morning, the only thing the printer knows is you have something blocking the light beam in the filament sensor - hopefully filament, not a screwdriver or something. So it will happy start printing any GCODE you choose.
It is up to YOU to make sure that the GCODE you load and the filament you load, are copasetic. Sometimes even that can be iffy. Take the sit where you slice for generic PETG but then load high temp PETG like prusament. Result? Might be balky extruding, and the print will be brittle because layer adhesion will be low.
This is why if you download a GCODE, you are mostly blind unless you open it up to see what temp it prints first layer and then changes to second layer. If you download a .3mf file, you'll pick up the choices that someone else made when they orginally set up the file in a slicer. If you don't know what those choices are, you could experience the same kind of balky extruding - because you didn't check!
I say it often - it's not a toaster. It's a complex robot that has been tamed with sophisticated tools that require quite a bit of attention from the human that is attending to the robot. There may be lucky times when you get a gcode file that is using the same filament profile you happen to have loaded when you happen to choose to print it - but the printer doesn't know what you have loaded - ever.
RE: No extrusion after filament change?
Thank you Dan.