2 issues: Multiplexer block/PTFE interference and possible heat creep
Hi all,
I was wondering if anyone else had a similar issue with this during assembly. Basically the PTFE tube that goes into the hotend was a tad too long and would not let the multiplexer block seat all the way down. See the pictures below. I trimmed the tube a little bit so I could seat it and insert the bolt through the side. I made a few single color prints and everything was fine.
Then during my 2nd multi color print (doubt this is related) the hotend became plugged. After disassembling the hot end I found that it had plugged up just before the heatbreak, in the cooling side of the hotend assembly. Not really sure how this happened, I am assuming heat creep up into the cooling side. Maybe inadequate cooling? I reassembled everything using the heatbreak coupler from the old hotend and will test tomorrow. (not sure if heatbreak coupler is the name, but it screws into the heating block and heat sink.
Re: 2 issues: Multiplexer block/PTFE interference and possible heat creep
the old heatbreak tube has different dimensions to the MMU one, slightly larger bore on old one, not internally polished.
was your PTFE liner flared and chamfered as recommended?
PJR, has shown a picture in the thread below
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
Re: 2 issues: Multiplexer block/PTFE interference and possible heat creep
Was the PTFE tube too long or was it not seated correctly in the heat break?
I would suspect the latter, thereby leaving a small gap for the blockage to occur - see my thread regarding blockage troubleshooting: http://shop.prusa3d.com/forum/original-prusa-i3-mk2-multimaterial-f26/blockage-troubleshooting--t4643.html .
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: 2 issues: Multiplexer block/PTFE interference and possible heat creep
The PTFE tube was fully seated into the heatbreak. But I did describe the position of the blockage improperly. It occured where the cold zone starts, not where the PTFE tube seats. The tube I shortened was re-chamfered before installing.
@joan.t - I'm curently soaking the heatbreak in acetone to help loosen the ABS that's jammed in it. I will try and clean it out and re-use that one before using the one from the old nozzle.
Re: 2 issues: Multiplexer block/PTFE interference and possible heat creep
It appears the heat break tube has a step inside the hole. I believe this is what caused the jam. The filament feeds into the side shown and gets caught on the step.
I'm going to try and smooth this step out while maintaining the same diameter on both ends.
Re: 2 issues: Multiplexer block/PTFE interference and possible heat creep
Yup.
The heat break is drilled from both ends and when drilling from the second side it may not be mounted in the chuck as accurately as it should be; the drill can also go off course a little.
E3D say the tolerance is 0.1mm, but I think it could be as much as 0.5mm.
This really does need burnishing or reaming after drilling; (note this is the only time I would suggest using a drill) with a 1.8mm drill bit, you can try to burnish the hole. Insert the drill bit fully into the heat break, turn on the drill (not too fast) and move the drill bit around the inside for a few seconds. The flutes on the side of the drill bit will hopefully reduce the step, effectively polishing it away. Use a light machine oil and stop the drill before removing the bit from the heat break.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: 2 issues: Multiplexer block/PTFE interference and possible heat creep
Thanks for the tips PJR. Though I am a machinist by trade, the detailed suggestion should be good for those who are a novice to metal work and run into the same issue.
I was able to get 99% of the step taken out and re-polished with some 600 grit sand paper twisted up and one end loaded into a cordless drill.
I'll get this thing installed late tonight and hopefully try some more prints tomorrow.
--HD
