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Sli3er settings for overhangs

Posted by Squags 
Sli3er settings for overhangs
January 29, 2014 03:05PM
Hello all,
I've been trying to print a few parts with moderately significant overhangs and was wondering whether I'm missing a trick as I've not had much joy.

This thing: [www.thingiverse.com]
for example has a flange at right angles to the tongs half way through it's thickness. Thanks to recommendations on this forum I've stopped the part from warping (195/70 down to 180/65C for the following layers), but the flange is still very stringy and unpleasant looking.
The one time I used 'supporting material' setting on sli3er, it made something so robust it was too difficult to remove. All suggestions welcome smiling smiley
Re: Sli3er settings for overhangs
January 30, 2014 04:42AM
I would try reducing the fill density of support material in slicer
Re: Sli3er settings for overhangs
January 30, 2014 12:05PM
I can't see how a pure overhang would work, and the only times I have printed pieces with overhangs, they have come out stringy. So when I design parts, I stick to the 45 degrees rule. Bridges are a different matter, they can work OK as long as they are not too long.

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Sli3er settings for overhangs
January 31, 2014 08:18AM
A 45 degree overhang means that the perimeter at the overhang extends out by the layer height every layer - usually 0.24mm for standard Slic3r settings. With a perimeter width of .5mm (also standard), that means that just over 50% of the extruded width overlaps the previous layer's perimeter. In my experience it doesn't require that amount of overlap - in fact for many shapes it works absolutely perfectly with no overlap at all (the infill will subsequently provide the support), which means that going out by .5mm every layer is fine - that's a slope of .5mm out every .24mm up, or about 2:1 - more than 60 degrees from vertical. By keeping the same perimeter width but reducing the layer height I suspect you could do a lot better.

I designed a part where I overlooked the fact that it had an unsupported 5mm square 90 degree overhang. I realised after I had started the print, but decided to allow it to continue. To my amazement the overhang did not print too badly at all. As the head moved to lay down the perimeter of the section that hung out in mid-air, the extruded filament (ABS) cooled and set fast enough that it held the shape of the rectangular head movement quite well, and ended up with three sides of an open 5mm square loop of plastic thread suspended from the wall of the part, which drooped down only slightly as it was subsequently filled. The following layer thus had a loose, droopy support, and did not sag very much, and the third and subsequent layers did not sag at all. I reckon that if the overhang was just slightly bevelled so that each layer extended out by 1.7mm (just over 3 times the perimeter width), it would have worked out fine. At .24mm layer height a 1.7mm overhang works out to a slope of almost 82 degrees from vertical ( ATAN(1.7 / .24) ).

Of course, the above assumes that the overhang is a relatively short section coming out from the body - you couldn't have a long section of perimeter hanging in mid-air with no solid support at either end. A short pin or ledge coming out of one side of a part would be OK, but not a ledge around two adjacent sides of a block, or around a cylinder. (From observation a short square section prints in mid-air with support along just one side, but not a curve). You could possibly print a hanging curve by setting Slic3r to print the infill before the perimeter, and setting only one perimeter so it touches the infill when printed.

The above is theoretical based on observation, and when I get a round tooit I'll do some experiments to see how the theory works out.

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