Blobbing on overhangs w/ ABS

Filament
1

I’ve tuned my TAZ (1.0) to the point where I get really nice prints in just about every case except one: overhangs.

I’m printing with the Lulzbot stock 3.5mm draft Slic3r config other than changing the filament diameter to 2.84mm, layer height to .2mm instead of .3mm and first layer height to 150% instead of .35mm. I’m using natural 3mm ABS from Ultimachine at 220C.

I’ve printed an ooze/retraction test from Thingiverse (http://www.thingiverse.com/thing:15087) at least 6 times with retraction settings ranging from .5mm to 5mm and nothing changes. Some prints are slightly better or slightly worse, but they all have significant blobbing on any of the overhangs.

I also tried printing the little Maker robot (http://www.thingiverse.com/thing:40212) Make Magazine used in their 3D printer tests this year. I’ve attached an image of it. You can see in the shadow under the left arm how bad the blobbing gets. This was the default Slic3r config I mentioned earlier (default retraction of 1.6mm as well).

Photo Nov 15, 9 18 21 AM (HDR).jpg
Photo Nov 15, 9 18 21 AM (HDR).jpg2448×3264 1.25 MB

I know I can print with support, but it looks like plenty of other printers can make this work without support, so I have to think I’m missing some type of tuning/configuration somewhere. Does anyone have some suggestions that might help with overhangs like this other than using support?

  • Adam
2

My 2 cents:

  1. Cooling the extruded plastic immediately after it comes out of the nozzle should help with this. I know some users have attached a fan to blow on the part as it prints. This is especially useful when printing with PLA, but the same idea applies to ABS.

  2. You could also try lowering the extrusion temperature from 230c a little bit so that the temperature of the plastic coming out of the nozzle is closer to the temperature at which the plastic is solid (you may have to slow the print speed a little when you do this).

  3. The development version of slic3r has a ‘start perimeters at non-overhang points’ checkbox that might help, too.

  4. If all else fails, you can try opening the file up in your favorite CAD software, cutting the model in two such that there are no longer overhangs, printing each half separately, and gluing the two halves together with lulzjuice.