Leaking hotend?

Hi folks,

I just finished building a Prusa I3 MkII printer kit and I'm having an issue I can't seem to figure out. This is my first experience with 3D printing, so please excuse my ignorance if this is something obvious. I believe I've gotten everything set up and pretty much calibrated the way it's supposed to be, but the problem I'm having is that the hotend is leaking filament pretty much constantly whenever it's hot enough to melt the plastic, at least until all the plastic has leaked out. It's leaking out the hole it's supposed to come out of (I'm sure there's a term for it, but I don't know what it is), not anywhere else.

I can insert filament and feed it manually from the Manual Control tab in Repetier, and it will extrude a good bit of plastic quickly, but when I stop feeding, the plastic keeps slowly leaking out of the hotend tip for several minutes. It will leak out several centimeters of plastic, enough to make a real mess. I can retract the filament several millimeters, but the stuff keeps leaking out the tip until it's empty.

I was under the impression that the printer would have very fine control over the flow of plastic out of the tip, but whenever I try to print something, the plastic flows out pretty constantly and doesn't stop even when I'd think it should. It makes a mess of pretty much everything. When I get it to print something simple, like a small cube, it will kinda work, but it looks to me like there's too much plastic flowing and the cube will end up misshapen. Anything more complicated, it will just print a glob and start dragging it around the bed.

I'm using PLA, temperature varying anywhere between 190 and 215 with same kind of behavior. I've verified that the filament feed and retraction are happening by marking the filament and watching it move. I'm thinking I might have a defective hotend, but I'm not sure what kind of defect would cause this. Any thoughts?

Thanks in advance,
Rodney

Filament will ooze out of the nozzle when hot, especially with a bowden setup.

Edited 1 time(s). Last edit at 12/18/2016 02:15PM by stephenrc.

Welcome to Ooze
What you experience is normal, especially for PLA. ABS and many other filaments will show it as well, but to a lesser degree.
It varies from hotend to hotend, but it happens with all of them. The larger the amount of plastic that can be molten at any time, the larger the amount of ooze. This means that big hotends, like the vulcano, that are build for high speed printing, will show it more than for example a Merlin.

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[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

I figured a little oozing would be normal, but this seems excessive, like when you stop feeding filament, it keeps flowing until everything in the nozzle has flowed out. If I start a print from cold, by the time everything heats up and the actual print starts, there is a huge tangle of plastic strands around the nozzle, plenty to mess up anything I'm printing. If I wait until it stops and clean it up before starting a print, it seems like the nozzle is empty and takes a few seconds to start flowing after the filament starts feeding, so the first layer or two don't get printed. Is this normal?

I print PLA with a Bowden setup with my flsun Cartesian and I'm not experiencing oozing anywhere near the degree described here. I'm just a newbie myself but I would think that this problem isn't normal and isn't something to just be lived with. My experience is about 10mm of ooze at extruded diameter, not filament diameter, as it warms up to temp before a print start. My first ASSumption is that heat is traveling too far up into the extruder body. What sort of heat sink and fan does your setup have?

I don't know how you'd describe my setup, I think it's a Bowden. It's what came with the RepRap I3 Mk2 kit. Picture is attached.

Also attached is a pic of the amount of filament that came out AFTER I canceled a running print job. It took this about a minute and a half to finally stop leaking, then after I cleaned off the tip and started the next job, it took about ten seconds for any material to start flowing after the print started, so the first layer was completely skipped and the print was ruined.

It is a direct extruder, not a bowden. A bowden setup has a teflon hose (bowden) between the extruder and the hotend, in your setup the hotend is directly mounted on the extruder.
You can't prevent the oozing completely, but you can add outlines at the beginning of the print to make sure the hotend is filled up with filament again.

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[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

I can tell you that on my setup the heat exchanger is literally right next to the heater cartridge and nozzle. Your setup looks to have about 10-15mm between the heater and heat exchanger. I can see that whole section getting hot enough to melt filament making it available to oozing. If there is any way to get the heater / nozzle closer to the heat exchanger it will probably help. Here's a pic of how close my heat exchanger is to the nozzle.

If the oozed string you showed in one of the images is all that gets out it is quite normal.

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[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

Duckmang, I think you may be on to something. The whole extruder motor/fan/hotend/nozzle business came pre-assembled, but I actually had to take it apart and turn the heatsink around because the filament didn't line up with the hole initially, which could indicate some quality issues in the kitting process. There is a lot larger gap between the heater and the heatsink than in the pics in the assembly guide, so I'll try screwing it in closer and see what happens. I think it's affecting my print quality as well because there is so much melted plastic in the nozzle that the extruder is unable to stop and start the flow as quickly as it needs to (I'm an EE so I'm thinking in terms of too much capacitance). It seems like I'm getting more plastic than I should, and any small details just end up as globs. Thanks for the pointers.

Insulating the hotend may help as well with something like this
[www.ebay.co.uk]

"Too much capacitance"

I like the analogy.