Purging extruder after filament change
After I change filament, I get blobs of the old filament on the first dozen or so layers of subsequent prints. The blobs can be on the first layer or following layers. If I quit the print and restart it, blobs of leftover filament still occur. The blobs become less frequent over the first 10 minutes of printing with new filament, but there is still old filament in the pipeline because I can see it in the new prints, even though it stops blobbing and looks like it just mixes in with the new filament in the course of the next few prints. Eventually, it works itself out completely and the prints start coming out color clear. This started happening after I upgraded to MK2.5 and then MK2.5S. I had an extruder clog and had to replace the PTFE tube . I had to man-handle the old tube a bit to get it out. To clear the clog, I used a heatgun, not a torch, so overheating the heat break isn't likely to be the problem. Over the past few filament changes, I've heated the extruder to 20 deg F over the temperature of the new filament and run the new filament through the extruder (select No when it asks if the new filament is color clear) a few extra cycles to try to push any old filament through, but the problem persists. Attached is a picture of a recent orange PETG print. You can see the previous black filament is present in the new orange part.
I want to avoid messing with the extruder at this point because it took a lot of effort to get the MK2.5S to work to this quality and I feel like any physical changes to the build would be rocking the boat. Cold pulling after every filament change isn't desirable either, since this problem didn't occur with the original MK2S and cold pulls are a PITA. Can anyone recommend any non-invasive procedure that might help purge old filament before loading new filament? Thanks in advance... Van
RE: Purging extruder after filament change
I've had good luck so far using "cleaning filament" (like this one from Amazon) to clear out remnants of old filament, either when changing filaments or after jams, etc. I've seen comments online that cleaning filament is not really anything special and doesn't do anything that normal filament wouldn't do, while others swear by it and claim it works much better at adhering to bits of old filament in the hot end and pulling them through. I don't know which opinion is true, but it was fairly cheap and uses such a small amount at a time that it will last a really long time, so I figured why not give it a try? So far, it has worked for me, but I'm new to this and can't really say if it works better than just pushing the new filament through in an equal quantity.
RE: Purging extruder after filament change
I've had good luck so far using "cleaning filament" (like this one from Amazon) to clear out remnants of old filament, either when changing filaments or after jams, etc.
I second eSun cleaning filament. It's flexible enough not to snap, doesn't create a stringy mess and does a good job capturing other filament remnants stuck in the hotend and nozzle.
I've seen comments online that cleaning filament is not really anything special and doesn't do anything that normal filament wouldn't do, while others swear by it and claim it works much better at adhering to bits of old filament in the hot end and pulling them through.
The big plus to cleaning filament is the wide range of temps it melts over. While it's true that you can use ABS or nylon for doing cold pulls quite effectively, the problem is if a bit of it gets stuck in the nozzle or hotend, itself contributing to problems when you try printing with lower (e.g. PLA) temps. A proper "cleaning filament" can work at 265C, but also be extruded at 200C.
I don't know which opinion is true, but it was fairly cheap and uses such a small amount at a time that it will last a really long time, so I figured why not give it a try? So far, it has worked for me, but I'm new to this and can't really say if it works better than just pushing the new filament through in an equal quantity.
One common reaction is to compare the price of cleaning filament to a 1 Kg spool of normal filament. The cleaning stuff comes in small quantities, but you only need 6in/15cm at a time, so it does last a very long time. I'm still on my 1st roll of eSun after 18 months and I use it with every nozzle swap and material change.
RE: Purging extruder after filament change
are the blobs coming thru the nozzle or are they dripping off the heater block. i suspect either you have a leaking nozzle/heatbreak connection in the heater block or a dirty heater block.
RE: Purging extruder after filament change
Image is not working for me. Try dragging & dropping it into a post here and be sure to set it to a large size for visibility.
RE: Purging extruder after filament change
are the blobs coming thru the nozzle or are they dripping off the heater block. i suspect either you have a leaking nozzle/heatbreak connection in the heater block or a dirty heater block.
The heater block or nozzle sounds likely. OP should raise Z and inspect both. Heat the nozzle up and use a soft brass wire brush to clean the block and nozzle, being careful to avoid the fine wires. If using a coated nozzle, a strip of cardboard can be used to wipe gunk off at temp.
RE: Purging extruder after filament change
There is gunk on the underside of the heater block, usually after a PETG print there's quite a bit of it, but I thought some ooze down there was normal. I remove the excess gunk from the bottom of the heater block regularly, there's always more after a PETG print. I disassembled the heater block assembly after the last major clog when I replaced the PTFE tube, but I don't remember removing the heatbreak.
It's interesting that this problem was much worse a few months ago, so bad that I couldn't get a good print at all. I put the printer on the backburner for a while and didn't do any printing at all. Just a few days ago I upgraded to the new firmware and Prusa Slicer, and was pleasantly surprised that besides this little issue with the unpurged filament, I am able to get good prints again without taking any hardware action.
Another possible cause is that when I replaced the PTFE tube, like I mentioned, I did some rather energetic pulling on it to get it out and mangled it up pretty good, not realizing that there was filament fused inside it that was preventing it from coming loose. Eventually, I heated the fused filament with the heat gun and got the mangled PTFE tube out, but I did not replace the retaining collet. In the meantime, I ordered a couple replacement collets but did not install them, as the prints are looking OK except for this non-purging of filament issue.
The reason I'm posting is that I don't know if the amount of previous filament that's stuck in my extruder pipeline is normal or if there is actually a hardware problem that needs fixing. The image is included (didn't know you could do that).
You can see the black filament residue in the orange part. That is the first finished part after the PETG color change from black to orange. Parts come out successively cleaner, until after about the 3rd one in this run of this part there is virtually no black residue to be seen. When switching from PETG to PLA I have to abort two prints after the 3rd layer due to blobbing of PETG residue, then the PLA prints come out OK.
So, folks that have used cleaning filament, does this describe the behavior that the cleaning filament helped you to fix? And if what you see here is excessive, could this behavior be explained by a damaged Bowden collet?
BTW, another interesting thing... when running filament through the extruder (i.e. when changing filament) I've heard it's supposed to curl. Mine doesn't, it just flows out straight all the way down till it hits the heatbed.
Thanks...Van
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RE: Purging extruder after filament change
[...] So, folks that have used cleaning filament, does this describe the behavior that the cleaning filament helped you to fix? And if what you see here is excessive, could this behavior be explained by a damaged Bowden collet?
Cleaning filament will help purging the previous material (provided you run it at a hotter temp) at which point there shouldn't be any remnants left in the hotend or nozzle to foul your print. Those sorts of blobs look more like something dripping off the exterior of the hotend. Next time you have the extruder housing off, look to see if there is any filament leaking from anywhere but the nozzle opening, particularly where the nozzle, hotend, heatbreak and heat sink are joined. If filament is collecting and burning, it'll drop off in little drabs throughout the print.
BTW, another interesting thing... when running filament through the extruder (i.e. when changing filament) I've heard it's supposed to curl. Mine doesn't, it just flows out straight all the way down till it hits the heatbed.
Good news: You've got it backwards. Filament curling back or flowing irregularly can indicate a partial clog. If it's flowing cleanly and straight out of the nozzle and forming a neat little coil at the bottom, that's a good sign.
RE: Purging extruder after filament change
Those sorts of blobs look more like something dripping off the exterior of the hotend. Next time you have the extruder housing off, look to see if there is any filament leaking from anywhere but the nozzle opening, particularly where the nozzle, hotend, heatbreak and heat sink are joined. If filament is collecting and burning, it'll drop off in little drabs throughout the print.
OK, I'll keep an eye out. What I don't get, though, is if it were leaking from somewhere other than the nozzle opening, how could the old filament it mix so cleanly with the new filament, such that the layering remains completely even? It seems like it's mixing in somewhere above the nozzle and extruding normally through the nozzle. Once the blobbing stops there's no sign of anything amiss, besides the strange filament color mixture.
That is definitely good news about the curling. That means that for the moment, I'm going to get some cleaning filament and get back to printing.
Thanks for all your help... Van
RE: Purging extruder after filament change
I've had strands of burnt filament drop onto a print, then get nicely blended in when the hot nozzle moves over it.
If it were truly mixed in above the nozzle, it wouldn't stay in one area and would be spread evenly throughout the layer being printed.
RE: Purging extruder after filament change
OK, I finally accepted that there were multiple issues here and contacted Prusa support. Looks like when I cleared the clogged hotend, I did not heat the nozzle when reassembling it. Also, the collet likely was damaged because after sending them this video, they are sending me a replacement. This shows the excessive of play in the collet.
Also, they pointed me to these hotend assembly instructions...
https://e3d-online.dozuki.com/Guide/V6+Assembly/6
They're also sending me a new thermistor because I've soldered the old one twice now because the micro-wire keeps chafing and breaking due to the uneven heatbed connection cover on the original MK2.5S kit.
So, thanks for pointing out that something was amiss. I've had a lot of trouble with this MK2.5S and I'm looking forward to getting all the issues cleared up. It's been quite frustrating.