burnt material oozes out of heat block

Hi, I made n Core XY printer with chimera dual nozzle, I use Clear PETG at 250 Celsius, and a very sticky burnt clear material oozes out of the aluminum heat block at the entry of the heatbreak and pours downwards to even cover the nozzle. it happens every time, and oozes on the print as brownish plastic blobs, can anyone tell me why is this happening...thanks

This usually happens if the hotend parts are not screwed together tight enough. They basically seal by deforming slightly. Depending on the hotend it is a delicate act to find the point where it is tight enough without ripping the heat brake.

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[www.hackerspace-ffm.de]

thank you very much, appreciate your answer

Ah the bane of my 3D printing experience.

This is very difficult to clear up. I basically had to replace all of the hotend parts, heat break, block and nozzle before I could clear this up.

[e3d-online.dozuki.com]

If you disassemble the existing parts, you can probably clean them up adequately by running a thread tap through the block, and a die over the nozzle and heat break, then carefully cleaning the mating surfaces of the heat break and nozzle so that they will fit together with no plastic whatsoever between them. Very fine grit sandpaper (5000+) on a block or a lapping block will be required to get a proper mating surface. Honestly, it's easier and more certain to start with new parts, there.

The parts in that wiki that you do need to pay attention to are the part that deal with the heat break and nozzle, up to where you hot tighten it. Anything outside of that will depend on what you're using.

From a mechanical engineering perspective, this is a terrible way to seal a joint, but it's what we've got. I'd feel much better if the nozzle and heat break were one piece, and the heat block were just run down the threads to the end. Or if there were a high temperature gasket between the pieces to seal it, but this is what we get.

On one of my printers, I've resorted to high temperature silicone [www.permatex.com] to seal the heat block. The other is now adequately sealed as per the E3D instructions. You shouldn't need the silicone, but the one printer that I have just wouldn't behave without it.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Also... Tightening the joints (nozzle-to-hot end, hot end-to-throat, throat-to-heat sink, etc.) while the hot end is hot makes a difference.

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-David

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everything else will result in what you have now and/or damaged parts.