Thursday, April 05, 2007


Getting the drift under control

I went back and programmed the PIC 18F4610 to do the things it ought to have been doing instead of depending on the overshoot hack like I was before. This is MUCH nicer than before.

The drift pretty much went away. I put in the maths to keep track of the absolute position of the extruder head and I'm down to a 5 pulse overshoot correction now. I set the first layer to smear, which seems to provide enough of a footing for the perimeter I'm printing to keep it from peeling.

I'm getting blobbing at the corners, but that is because I'm not turning off the polymer pump when I reach the end of an extrusion path and I'm pausing for 100 milliseconds between line segments. Otherwise the layering is looking very good.

The extrusion thread as put down is right at 1 mm wide and 0.5 mm high which is just about right for a 0.8 mm extrusion thread. The HDPE is pigmented white and looks just like toothpaste being extruded from the Tommelise Mk 1. It's a pleasure to watch in operation.

I'm getting to feeling really good about HDPE as a polymer for 3D printing.

Looking good. I am glad the HDPE looks promising as I am surrounded by milk bottles at the moment.
Figure out how to build a grinder than can turn them into granules that will go into a filament extruder and we're home free.

We pretty much know how to make the filament extruder, but nobody has worked on a plastics grinder yet.
very nice! i was thinking about the problem of adhesion last night and was going to suggest having the first layer smear on the print surface. seems like you got to it before i said something.

good work!

how about tweaking the code to not pause / stop the extruder? seems like its worth a try =)
I have passed some HDPE milk bottles through a cheap crosscut paper shredder. I cut them with scissors first so they are reasonably flat. After the first pass they form strips but they are held together by thin transparent webs. I think stretching a polymer can make it get stronger.

Multiple passes results in small chips but it hard to do because the throat of the shredder is too thin for safety reasons. When I get a chance I will open it out and see if it is practical to pour shredded bits back in. I suspect the shredder may not last long with this kind of abuse, but you never know. Paper is very abrasive so may actually be more wear on the blades than HDPE although I expect the plastic takes more mechanical effort to shred.
Nice going Forrest! Looks real good.
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