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Another support material miracle?Saturday, May 19. 2007
While
I was doing some practice prints last night to get used to printing on
duct tape something very unexpected happened. Recently, I've been
working to get the polymer flow rate coordinated very closely with the
extruder head velocity. Last evening I accidently managed to do that
with a heretofore unencountered precision in a peculiar situation that
produced some very interesting results.
I had laid down an HDPE raft and was trying to print a layer of the Mk 1 polymer pump on top of that. I had had trouble getting the layering interval right and managed to get it about 0.75 mm higher than it should have been. Ordinarily, that would have just made a mess of squiggled extrusions instead of a print.  All the same it made for a rather messy print as you can clearly see. It had been a long day and I had demonstrated that I could successfully print on HDPE, so I nearly just packed it in and went to bed. As I was shutting Tommelise down, however, I reached over to turn off the worktable light and in doing so noticed a very consistent shadow under the right hand side. I'm very used to seeing that sort of thing when the extrusion doesn't adhere to the raft. In this case, however, the shadow was long and even rather than short and humped. I hadn't seen something like that before, so I used a small metal rule to see if I could determine the extent of this gap.  If I was intrigued before I was astonished when the rule easily slid fully 7 mm under the extrusion.
Further probing revealed that I had spanned a gap just short of 50 mm long and 7 mm deep with a horizontal extrusion.
 You can see the extent of the span outlined in blue. Now the question arose as to how this happened. I haven't got perfect on/off control on my extruder. When the firmware pauses just a fraction of a second between extrusion tracks that leaves a bit of a blob.  You can see two diagonals where these blobs formed when I turned a corner with the exturder circled in red. In this very peculiar print I built the extruder layer from the inside to the outside perimeter by following a track around an initial "t" till I had the section finished. You will recall that the print layer was accidentally set 0.75 mm high. The cornering blobs were big enough to touch down onto the HDPE raft and weld to it while the regular extrusion wasn't. Because I had the flow and the extrusion speed just about perfectly matched for this section the new extrusion track welded to the cold extrusion track beside it instead of falling down to the raft and welding to that. What I wound up with was a completely horizontal span across nothing but air for an astonishing distance. Think what this could mean in terms of printing things if we could do this regularly. Mind, I suspect that if I tried to put another layer on top of it I might well soften the span to a point where it slumped to the raft. What it demonstrates, though, is that we can span gaps at angles considerably shallower than 45 degrees if we are carefull. Trackbacks
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"I suspect that if I tried to put another layer on top of it I might well soften the span to a point where it slumped to the raft."
Only if you laid the second layer down in the same direction. If you fill it in with tracks perpedicular to the existing layer, you shouldn't have that problem.
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