Friday, April 4, 2008

Rework

Having a lot of trouble getting a reliable extrusion. I had two PTFE barrels, both of which are distorted too much to be useful. I had two extruder clamps (one quick-fit, one regular). Both have suffered heat damage.

See, here's the problem I'm running into. Plastic, when subjected to heat and pressure, tends to sag. This means that, under normal operation for extruding HDPE, the nozzle tends to edge downward. I've had a couple tests so far where everything started out fine but ended up with the nozzle grinding into the bed.

I'm beginning to think that the current extruder design just can't do HDPE reliably. It wasn't really designed to do it in the first place.

Current plan: Rebuild extruder using stronger components. I've got a 1" diameter piece of PTFE on order. I might end up making an extruder clamp out of MDF. I think I'm going to buy some CAPA to see if it's any easier to use.

3 comments:

nophead said...

Hi Steve,
You have to allow for the PTFE expanding ~0.5mm when hot so you need to calibrate the z axis when it is at the temperature you extrude at and has been running a while, because it creeps a lot to start with.

I managed to make it reliable with 16mm PTFE plus the pipe clip and limiting the temperature to 220C. Ideally it should be 240C and have a fan blowing but that is too much for the PTFE and JB Weld.

Insulating the nozzle and leaving the PTFE uninsulated should help.

CAPA does not stress the PTFE, I found it stresses the motor more than HDPE though.

Regards, Chris

nophead said...

PS, if you are damaging the clamp perhaps the temperature is higher that you think it is. I published temperatures here http://blog.reprap.org/2008/03/extruder-temperatures.html

and the top end of my PTFE is only 47C. I assume you clamp is PU, not PCL.

Webcam said...
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