Tuesday, December 11, 2007


Wiping up

The nozzle oozes a bit for a few seconds after the extruder motor's been shut off. Naturally the dribble spoils the build a bit, so I thought I'd try building in a wiper to clean its noze before each layer. The framework comes off the diagonal, and looks a bit like an intergalactic spaceweapon. Things under test so far are razor blades and car windscreen wipers.

I'll keep you posted.

Excellent work, but the design in the current picture is relying exclusively on the strength of the locknuts to stop it rotating out of position about the diagonal rod. I'd suggest a more solid mounting, just in case it tends to work loose over many cycles of operation - the sort of bug that can cause a lot of misinterpreted drift in results before it's spotted.

Also, might it be worth trying the razor blade perpendicular to the plane of motion of the nozzle, or some angle in between so that it slices off the excess rather than scraping? Not sure which might work better, probably a matter for experimentation.
Am I right in gathering that you are extruding HDPE?
Make sure you review nophead's research on this. Especially relevant was his observation that a brush worked better than a knife: http://hydraraptor.blogspot.com/2007/10/brush-off.html
Tom: Thatnks, yes the current bracket is currently widly under constrained. This is because of a lack of structure anywhere near a feasible wipe zone. More solid mounting would be great, but so far the wipe force has been so low that the nuts are catering with safety factor to spare. Also, yeah, angled wiping seems to work well too.

Forrest: We're doing capa this end

Beaglefury: Thanks for the lead. I've bought some toothbrushes today with similar intentions. Smokers to the rescue: the hardest bristles!
Why the elaborate mounting, why not fasten it to the table?
Because, if I'm not mistaken, the table would then have to traverse back up from wherever it was every time the wiper was needed. This may not even be possible if whatever work in progress is so shaped that it crashes into the extruder in moving back up again, and it also means you'd have to accurately return the table to its working position every time. That would add a lot of unnecessary runtime overhead as the table traversed for each necessary wipe, in addition to the potential collision/allignment problems that might arise.
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