Can't stop heat creep - please help

3d ers,

I've been trying for months, but always end up at the same spot.

In short, I can't print pla due to heat creep in the tube. My da Vinci with official nozzle from xyz that supports it, as well as my i3 build. On the i3, I have been through different nozzles, including j head, mk7, and my latest purchase of a Pico extruder.

This happens at all temps, 185-205-230, etc... I can get it flowing, but it will always expand in the tube and cause clogs. Fun, right?

Even when trying to isolate the tube with this:
[www.thingiverse.com]

It doesn't matter. What am I doing wrong? -and thanks for any help.

have you got a fan cooling down the upper part of the hotend?

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Thanks for jumping in.

For my i3, I'm using a print of the fan shroud on Thingiverse for the Pico hot end. I also have an additional fan that I mounted directly to the left of it, and am directing it's airflow towards the extruder.

For the DaVinci, it's just using the stock fan assembly that comes with it. *When you purchase a hot-end from XYZ, they send it already assembled in their quick-release carriage.

So, yes on both counds. The i3 has 2 fans that I wired in, while the DaVinci has one - Unfortunately, neither seem to be able to stop the PLA from expanding in the tube and getting blocked.

Up next, I may try this: [www.thingiverse.com] - Looks promising.

Make sure you have your i3 hotend fan wired directly to the power input on the control board and bypass the fan control. The hotend fan needs to be on all the time, and also need to be left on after the print completes to allow the hotend to cool off without heat traveling up it.

Can do... but I've already done this in software. In Cura, I edited the G-Code for prints.

It had a M107 (disable fan) - and left it off for the first layer. I changed this to a M106 (enable fan). At the end, I also put a M109 60 (set temp and wait until temp is reached *60c) before disabling the fan. Both commands do what they're supposed to and the fans stay on throughout the entire print.

Edited 1 time(s). Last edit at 05/17/2015 10:36AM by usslindstrom.

I've seen forums adding PTFE tape to the throat in order to fight leakage. You guys think this would also help to keep some of the heat transfer at bay?

I use glass matt with kapton tape around the heat block and I use a e3d style tip with a fan shrowd, never have heat problems any more.

Ehhh.....
A better cooling fan is the only option if you're using an all metal extruder. Glass and/or ceramic connections would also stop alot of that sorta stuff but neither has been well developed for some reason.

With regards to heat creep, it's possible that retraction is the issue here. As the printer feeds filament down into the hot end, if it pulls back some semi-molten blob, that would carry heat with it. If you're machine does allot of retracting, that could cause the heat to steadily creep up the metal extruders, even with a fan.

As far as leaking PLA, use clear RTV silicone.
It's heat stable, chemically resistant to just about everything out there, and it's excellent for preventing liquids from seeping through stuff. After it sets, I've found it to be trouble free, but it does require a small amount of insight to use.

Qcks, you win the RepRap interweb!

Looks like it was 100% related to retraction. I calibrated everything under the sun on both of these machines, but didn't touch the retraction settings. After your comment pointed me in that research direction... I ended up taking the default Marlin setting of retraction acceleration from 500, and setting the value down to 300. (There's a formula that would get the exact number, but in all the forums/related posts I was able to see on the topic everyone pretty much settled at the same number - or very similar).

After slowing that bad boy down, it looks like the blockage issues have been resolved. Much apprecated on the assistance here guys.