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Mendel 90 J-Head heat creep

Posted by ad7u 
Mendel 90 J-Head heat creep
March 23, 2018 02:14AM

I have a Mendel 90 that I built a few years ago and I am still having trouble getting consistent prints from it. I'm using the J-Head MK-V with 0.3mm nozzle.

J-Head MK-V 0.3mm nozzle
Pronterface 2015.03.10
Slic3r v1.2.9
Verbatim PLA @ 190C

It will print for a while, but as the print extrusion speed slows while printing the honeycomb layers it stops extruding. Pausing the print and reversing out the filament shows the filament expanded at the end.

I've tried a few recommendations from forums and googing:
  • switched from ABS to PLA
  • tightened the bearing that presses against the hobbed bolt for extruding
  • wrapping EZ-Fuse tape around the extruder head

I'm starting to wonder if this might have to do with either the extruder (got it on Amazon about 4 years ago, maybe not legit?). Or if the slic3r/Smoothieware might be extruding the filament too slow?

Before I get another extruder (E3D or J-Head V8 0.5mm?) and associated mounting stuff I wanted to see if there are other ideas?

Thanks in advance!
Re: Mendel 90 J-Head heat creep
March 23, 2018 03:29AM
You can set a minimum printing speed in slic3r.

Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Re: Mendel 90 J-Head heat creep
March 23, 2018 09:18AM
What are your print speeds ?
Is that honeycombe the infill ?
The honeycombe infill creates a lot of jerky movements so it seems sensible to print it slower than rectilinear.
If you change to rectelinear infill you can increase the speed. I typically print rectilinear infill faster than perimeters.
So you can try using rectilinear infill and printing faster. That reduces the amount of time the filament is in the hot nozzle and so reduces heat conduction up the filament.
We need to remember you have a 0.3mm nozle so all your speeds are likely to be slower than with the more common 0.4 nozzle.
Is this a bowden? Retraction distance can be an issue with bowdens and PLA.
I guess it can also depend on the filament and water absorption. How much does the filament expand when heated but not melted. Ive noted on home builds theres some variations on bowden tube diameter - some people are using 1.8mm bore with 1.75mm filament while others are using 2mm (generaly recomended).
Which does beg the question what size filament are you using? 3mm filament will feed a lot slower than 1.75mm with the resulting increased heat creap. IMHO small nozles need small filament diameter.
Re: Mendel 90 J-Head heat creep
March 24, 2018 05:22AM
You should definitely put EZ fuse tape over the heater block of the hot end. That makes a big difference to the amount of heat rising.

One user has had success mounting a tiny fan under the carriage to blow across the top of the hot end.

The normal nozzle size for Mendel90 is 0.4mm, so the filament will be moving slower with 0.3mm. There is a minimum flow rate with PLA, where no matter how well you cool the top of the hot end the heat creeps up the filament itself.

Re: Mendel 90 J-Head heat creep
March 24, 2018 10:38PM
It's a direct drive 3mm extruder with the EZ fuse tape.

I tried using the rectelinear infill and that didn't make a difference. I think I'll try getting a larger extruder. Any recommendations on .4mm versus .5mm?
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