Design for No-Support: 45 Degree Rule
The MakerBot and RepRap machines don’t have support plastics like the expensive 3D printing machines from Dimension, and while Skeinforge does have a “support gridding” option, at the moment you’re much better off altering your model so you don’t need it. Today we’ll discuss making shapes more print-friendly with a minimum of impact to the shape of the final object. The basic design rule is: no overhangs greater than 45 degrees. If you always obey this, odds are you will never have a problem with dangling plastic noodles.
This, however, is a rule that can be bent, and occasionally even broken, if you think ahead and in terms of 3D printing technology. One key: overhang is size dependent. A 2mm circular hole will print just fine with no teardropping, but a 2 centimeter hole will start to get droopy loops:
Droop is also a function of how long the overhang goes on for. If an edge of a layer is resting almost on thin air, but the noodle marking this perimeter only dodges briefly out over the abyss, it’ll likely hold firm, whereas a long trek can cause the whole thing to sag in the finished print. You can even get away with short horizontal jogs out into nothingness if they’re brief, especially if they have someplace to go. Note the test part with a square(!) horizontal cavity here:
The truth is that both holes will probably be usable, although you’ll have to file off a bunch of ugly hanging plastic on the cavity to the left. Horizontal overhangs shorter than a centimeter will often hold up just fine! Thingiverse has a few examples of print jobs that bend the rules but still come out okay.
And this is all well and good for mechanical designs– you’re going for function, not form. But what about your character designs? How are you supposed to effectively design a figurine or a fantasy structure if you’re worrying about the mechanical limits of the plastic deposition? The answer generally is: cheat! If your character has arms that hang by its sides, put them up on posts. If you have a dome, support it with pillars you can snap off after printing, like this:
If you’re really pressed, break your model up into pieces that can be glued together:
It’s best to think ahead from as early as possible when preparing these tactics of course– it can be a real nightmare to pick apart a model and add support structures or cut it apart.
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bogdan kecman Said,
May 18, 2010 @ 9:11 pm
I designed and made this test some time ago:
http://www.thingiverse.com/thing:1169
http://www.thingiverse.com/image:6156
http://www.thingiverse.com/derivative:858
It test overhang from 60degrees up to 20degrees (or if you count from another side, 30 to 70 degrees), and if your machine is properly calibrated (feed/flow and temperature) you can easily get 20degrees working properly. The very important part play the material temperature, for e.g. 235C ABS will print 20 degree overhang without a problem while 255C ABS will not even print 55 degree one (you can use fan to get it go up to 40 but that’s about it).
Erik de Bruijn Said,
May 19, 2010 @ 2:01 am
It mostly depends on how well your extrusion rate (material deposition) is calibrated with the feedrate (movement on XY).
I found that with thinner layers in general you can have higher-degree overhangs. Also, segments that are “overhung” (is that a word?) should be printed at half the height once and then normally because otherwise it will hardly touch the material below it. AFAIK there’s not feature for this in skeinforge or any other toolpath generator yet. You can combine several G-Code files with different layer thicknesses though (I use vi to search for the right Z-offset and remove the sections I don’t want and later ‘cat’ the files together into one).
If you want to know more, Bogdan and I discuss a wrapping effect possibly allowing much higher degree overhangs in some circumstances:
http://www.thingiverse.com/thing:1169
Printing with supports – more than one way to skein a cat - MakerBot Industries Said,
October 14, 2010 @ 6:03 am
[...] every printable thing on Thingiverse adheres to the “45 degree rule” for fused deposition modeling. There are some very clever ways around such problems – such as Zaggo’s treasure [...]
repair print head Said,
February 5, 2011 @ 4:42 am
It’s best to think ahead from as early as possible when preparing these tactics of course– it can be a real nightmare to pick apart a model and add support structures or cut it apart.
And They’re Off! Said,
January 30, 2012 @ 12:49 pm
[...] * Avoid “overhangs” of greater than 45 degrees (except when you can get away with them) [...]
MtDon Said,
January 30, 2012 @ 5:42 pm
Just to confuse newcomers to 3D printing some more, here are two more test things from thingiverse for checking how well a 3D printer prints overhangs and “bridges.”
http://www.thingiverse.com/thing:12925
http://www.thingiverse.com/thing:16503
And They’re Off! | 3D Print Plan | All about 3D Printing Said,
February 2, 2012 @ 7:09 pm
[...] * Avoid “overhangs” of greater than 45 degrees (except when you can get away with them) [...]
3D Printing Plan | 3D Printing News and Updates» Blog Archive » And They’re Off! Said,
February 5, 2012 @ 2:02 pm
[...] * Avoid “overhangs” of greater than 45 degrees (except when you can get away with them) [...]