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Prusa hot-end extrusion woes

Posted by Thingy 
Prusa hot-end extrusion woes
March 21, 2013 03:26AM
So I finally got around to fix my prusa.
Bought a new hot-end and a new glass bed that had broken.

I got the budaschnozzle v1.2 from ebay.
No instructions so fist I put it together all wrong and melted some parts trying to print with ABS.
But the extrusion wont work right.

At first it printed a few layers allright, but every now and then a layer or part of a layer get's no plastic extruded at all. It's as if the plastic get clogged in the hot-end. Aborting the print and trying to extrude spaghetti works without problem.

I have the 0.4 point printing at 0.2 mm layerheight.

I have tried different extrusion multipliers but none works for a whole print.
IU ma considering going back to my home made hot-end, atleast there it is easy to remove filament if the extrusioin is problematic.

I tried with blue painters tape first and that worked okayish, then I tired with ABS-juice, but that just made it print the first two layers, and would put plastic on the third. Still spaghetti is extruded.

I checked the temp and that stays correct even when it stops extruding.

IT seems as if the filament melts and it get deposited where the ptfe tube is.
Extruding slower would be the solution, but how do I find the optimal extrusion rate. I don't see when it is too much before it gets clogged. And taking the hot-end apart and clean it between each try would make that operation take a week nonstop work.
Any ideas?
Re: Prusa hot-end extrusion woes
March 22, 2013 11:48AM
exactly the same problem here..

while I have had very good prints for a while with the same hotend..

If I raise the extrusion temp, the clogging in the pfte tube gets worse.
Lower temp makes it mess some layers up.

Re: Prusa hot-end extrusion woes
March 25, 2013 01:29PM
I reverted back to my home made hotend.
Which works fairly well when I stole the heating element and thermistor from the budashnozzle.
I have a variant of the North90 hot-end which was the simplest model I could find.

I guess I had to somehow fit the included fan, blowing air on the copper heat sink, surrounding the ptfe so that it keeps from melting the filament that high up.
Or try to find an extrusion rate that's optimal, but neither of those seemed feasible, running an extra cable to the extruder for that fan seemed like overkill, and I don't know if the sanguinololo has power out pins for a fan.

The only problem left now is levelling the bed and finding out if the bed thermistor is faulty, it feels much hotter to the touch than the temp it reads.

Dirk, did you try with the 0.5mm tip? I never tried that one, maybe it flows easier and clogs less.
Re: Prusa hot-end extrusion woes
April 05, 2013 10:42AM
Nope, it's the next thing to try I guess. Pity, I like the resolution of the 0,35mm..

I hope to see other ideas before I pull out one of my tungsten PCB micro-drills smiling smiley
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