Leaking Nozzle

[jesse]

The threads on my stock nozzle are leaking black (burned?) plastic.

I've probably switched between 0.5mm and 0.7mm nozzles about 10 times.

The problem only occurs with the 0.5mm nozzle which I cleaned with a blowtorch.

Anyone else have this problem?

[bubbasnow]

so, around the brass nozzle and the alum hot end you have plastic coming out?

if so, i would pull the nozzle and ensure the plastic tubes that guide the filament towards the opening are installed correctly.

[GarageBay9]

I was having this issue with my hotend as well before it busted. Was getting a slow-growing curl of leakage from out of the nozzle threads.

[jesse]

I was having this issue with my hotend as well before it busted. Was getting a slow-growing curl of leakage from out of the nozzle threads.

Was the problem on the Nozzle or the aluminum heat block?

[GarageBay9]

I was having this issue with my hotend as well before it busted. Was getting a slow-growing curl of leakage from out of the nozzle threads.

Was the problem on the Nozzle or the aluminum heat block?

If I had to take a wild guess, iit looked like one of the hex faces was milled down just a little too far, leaving a gap between it and the aluminum body when at operating temp for ABS (230c).

[jesse]

Here's what the problem looks like.

[img]http://i.imgur.com/IyEltvUl.jpg[/img]
[img]http://i.imgur.com/9FVai9dl.jpg[/img]

Hopefully the new nozzle I ordered will fix it.

[626Pilot]

If you try to push filament through this hot end, but there is too much backpressure (often caused by PLA that's "melt creeping" up the inside - it degrades into brownish gunk if it's kept hot for too long) it will either make the extruder drive motor skip or take the path of least resistance, and sometimes both. The path of least resistance is to ooze up and around (and between) the PTFE liners inside the top of the hot end, out the place where the PEEK (plastic part) threads into the aluminum, and out the threads between the nozzle and the heater block. It happened to me a lot. I would bring the hot end up to about 200C, unscrew the nozzle, use pliers to pull out the PTFE liners, clean them off as best I could, then use my stove (which has an undocumented "blow torch" mode) to burn all the ick off of the nozzle. It worked alright, but after I had done it a couple dozen times I decided to try something different.

The problem with PTFE and PEEK is that they're insulators. They transfer heat, but only slowly, and they are susceptible to becoming heat-soaked over time. I've had any number of prints with hot ends using these materials that failed, but not until 15 or 20 minutes in, because that's how long it took the PTFE or PEEK to get heat-soaked.

I got a J-head from http://hot-ends.com. It's better than the stock hot end, but not by much. Heat sink fins are milled into the PEEK material. However, being PEEK, it doesn't want to be a heat sink. It wants to do the opposite! So while it performed better, it would still occasionally jam, usually in the middle of a print that I thought was going to succeed. (However, I really like the heating resistor they use. It's quick!)

Then, I tried a Budaschnozzle. The cooling design is novel - a PTFE tube with a bunch of aluminum heat sinks force-fit around it. At least they aren't using PEEK, but PTFE has the same problem as PEEK. It was better than the J-head, but I still had to spend more time figuring out how to run it just right than I thought should have been necessary.

Finally, I ordered an E3D all-metal hot end. This is the hot end to get. The heater block is stood off from both the heat sinks and the flange of the print nozzle, meaning that both of these touch the heater block with the minimum amount of metal required. As a result, the fan-cooled heat sinks are cool to the touch even when the heater block is at 230C - even the bottom one! - and the nozzle, whose flange doesn't touch the heater block, doesn't get heat soaked. Because there is no PEEK or PTFE anywhere, there are no thermal reservoirs to slowly accumulate heat and eventually screw up your print. It's now in its 5th revision and to my knowledge people who've tried it don't usually find a reason to go back.

[jesse]

Thanks 626Pilot. I tried a new SeeMeCNC 0.5 mm nozzle and the problem still occured. The hot end will be taken apart for investigation. The E3D seems pretty good, which bowden length did you order? Is it a good deal for about $100 USD ?

Do you think teflon tape on the nozzle threads would help?

[626Pilot]

I ordered the shorter of the two Bowden lengths. You already have PTFE tubing that will work with it. If anything I wish they had an option for no tubing, since ours is clear and theirs isn't.

Wrapping the threads in PTFE tape is a trick a lot of hot end makers seem to recommend. However, that stuff is a band-aid. If the design has heat dissipation problems that are bad enough to require PTFE tape, adding the tape may only slow down the problem, and again you have the problem with prints that start out great - and then 15 or 20 minutes in, you hear your EZStruder going thunk-thunk-thunk and the print is ruined.

N.b.: I actually wrapped the threads of the nozzle on my E3D with PTFE tape out of habit. It actually screws up the printing to do this!

[jesse]

For some reason, the problem only occurs for PLA. Probably from premature melting

[626Pilot]

PLA likes to enter a sort of gooey transitional phase between solid and liquid. Ideally, the melt zone is short as possible in order to limit this effect. What happens is that as the inside of the hot end heats up more and more, the zone where it's hot enough to turn into goo expands. As the filament heats, it expands as well, to the point where it grips the sides so well that the extruder can no longer push it through. That's when you start getting brown ick everywhere.

[jesse]

I stumbled across a solution. Run some ABS through the printer and switch to PLA. The ABS acts like a plug before the PLA can leak out from the threads.