Monday, June 14, 2010


Extruder Problems

Scott and I had our first RepRap session this evening. First off, we made sure the extruder was connected up correctly. When James and I were building Kurzweil a year ago, we lost the "12 Way Connector" that came with our BfB kit. We fudged a solution to get the extruder connected, but it's fragile, and got messed up during transportation across campus for the end-of-year poster session a month ago. Printing a new 12-way connector is an excellent candidate for a future project.

Once we were sure the extruder was connected properly, we performed the tedious but necessary rituals of bed-leveling and z-axis-setting (thus further fueling my desire for one of those well-constrained Mendels...).

We started noticing problems while printing the test rafts. The extruder was clicking, and I could see the filament jumping back, so I released the pressure bearings a bit. I may have gone too far, because the flow from the extruder became pretty feeble, so I tightened them back up half as much as I loosened them. That seemed to make the extruder run more smoothly but the flow was still pretty weak resulting in this test raft:
test raft

I think the problem is either in the tension of the pressure bearings, or some kind of clogging in the nozzle or the insulator, which, if you were wondering, looks like this:
bulgy insulator

I know that the bulge is a problem others have run into. The Bfb kit called for us to cut off a ring of the nozzle to restrain the insulator, but we didn't have the tools to do that and Ian at BfB assured us we'd be fine without it... I'll look around for solutions but if anyone reading this has a take on the situation I'd really appreciate the input.

YIKES! Is that plastic exploding out of that insulator?
That looks completely totaled!

Your insulator has bulged so far I cannot imagine it ever working at all.
I solved the minor (less than 1mm) bulge I noticed with a copper pipe connector (straight) and a pipe clamp.

Leaking from around the insulator is a surefire way to waste plastic and increase the force needed to push more through.

I think it is initially caused by increasing the temperature of the insulator too far, which allows it to expand, and molten plastic creeps up into it. Once in the insulator, it leaks into the threading on the heater barrel and may leak right out in a flange shape.

If plastic cools down in the insulator, it forms a plug, and this tends to make the plastic feed stall, stripping the filament. It may also permanently damage the insulator.

Looks like that's what happened here.
No, no plastic leaking (you may be seeing fire cement at the base, or a bit of the insulator the was scraped off by some pliers), but your description explains pretty much all of the problems we are having. Looks like we need an new insulator...
There should have been a BROWN PEEK-TUBE that should have been put around the white PTFE there.

Also your temperature must have been way too high for the PTFE to deform like that.
What was the temperature?
Can you make a detail-photo of the placement of the thermistor in the hot-end?
The deformation is after about a year's worth of VERY intermittent use, usually around 235C. Detail photo coming soon.
Oh wait, a detail photo of the thermistor? That's totally covered in fire cement... but Scott has Kapton tape and it's probably worth redoing to make sure it's right.
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