Helical coupling without support material

I'm trying to print a helical coupling without support material. It's got a pretty wicked overhang (about 75 degrees) but because the overhanging edge is convex, on the last perimeter, the filament is pulled in against the previous perimeter and it more or less hangs together. The print in the image looks pretty raggedy, but seems structurally sound.

The problem I'm having is not that the leading edge of the overhand droops - instead it wants to curl up. As subsequent layers are printed, it mashes down the curl but leaves things pretty rough looking. I'm using a 0.4mm layer height with 0.4mm nozzle. If I use too much fan, it still curls up but hardens completely so that it can't get pushed back down by the next layer. My best luck so far has been with moderate fan speed so that the leading edge is still a little rubbery when the next layer comes around. The final perimeter is done at 30mm/sec.

Anyone had any luck preventing the leading edge from curling up?

try printing it on its side, then if needed add brim support (singe layer at base) you may have a little bit of part clean up but structure is more likely to be shaped correctly without strings.

Yeah, printing it on its side would be the sane thing to do. Mostly I was curious about how far you can push overhang geometry if you tailor the shape of the overhang for optimal printing. (I shaped the cross section of the flexing beam to create a convex overhang.) I was surprised that I got curl-up instead of sag. To me this would indicate that if I can get the temps and cooling right so that I end up exactly somewhere between sagging and curlling-up, I should be able to get a pretty decent print without supports.

up to 45 degrees under optimum condition. that is as far as i could push it repeatably. after 45 degrees the top layer is no longer supported by the beneath layer. some tricks may exist to flatten a top layer and support wider and more flat bridging in thin air, but i have not seen something other than manually crafted gcode to do this on a case by case basis.

Edited 1 time(s). Last edit at 10/03/2013 09:05PM by jamesdanielv.

I find that lower layer heights allow greater overhangs without problems. At 0.4mm I get very poor (almost useless) quality even at less than 45 degrees whereas at 0.1mm I could easily get some 70 degrees or so. However at 0.1mm I get all sorts of unrelated problems so not very useful for me (until I sort that out). I am speaking here of normal flat surfaces not convex ones (which work better with overhangs)

What I would do is use the minimum layer height that prints well and turn the temperature and also the speed way down. Not only for the perimeters but also the loops and infill. Turning down the temperature will probably reduce the strength somewhat so don't overdo it. Slowing it down should do no harm though I guess, except that it will take much longer to print. The lower temperature and slower speed should eliminate the curling and also the sagging.

I don;t know if you're using PLA or ABS but in this I think cooling fans would help in either case.

The trick for better/steeper overhangs is small layer heights, min temps and as much cooling as you can manage. Can you link to an STL for that coupler, I'd like to try printing it to see how I can do.

Here's the STL for the coupler. I'll be quite interested to see how it comes out for you.

Blimey, is that coupling really only 1mm high?

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Waitaki 3D Printer

Sorry - I'm an old school guy. It's 1" tall.