The other day I designed a 3D printing project, set it up on the Ender 3 and left it to print. It was about three-quarters finished when I suddenly remembered that I’d been messing around with the settings in Cura and turned off supports. As the object I was printing had a two-inch-wide rectangular cut-out going right through the middle of it, it didn’t need a lot of imagination to work out how that was going to turn out: When the Ender tried to run a line of filament over the top of the cut-out it would simply collapse into the hole where the supports should have been, and I’d end up with yet another tangled bird’s nest.
Except that didn’t happen.
When I retrieved the finished 3D print, a couple of strands at the top of the cut-out had drooped slightly – and that was it. The rest of it had printed just fine. A quick scrape with a knife pretty much cleaned up the droopy bits, and while the top edge isn’t the neatest thing I’ve ever printed it’s perfectly acceptable for what is, after all, just a spool stand.
Now, here’s the thing: Why had I added the cut-out to the design in the first place? To save filament and printing time. And I was going to fill it in with a support that took time and filament to print, then went in the bin. It made me think, I can tell you.
Of course the support wouldn’t take as much time or filament as just omitting the cut-out; I print supports at 10% density, while the spool stand has 40% infill and thick walls. Still, it takes more than empty space does. Have I been printing supports where they weren’t actually needed? I decided it was time to do some testing.
Testing Without 3D Printed Supports
The first thing I did was download a 3D printing test file. This is an interesting little thing with a lot of challenges built into it, and it probably deserves a post of its own at some point, but why I printed one is that it has a series of bridge tests. These range from two to 16mm long, and clearly the test’s designer thinks it’s worth testing a printer’s ability to do that.
But even allowing for the rounded corners of the cut-out in my spool stand the Ender 3 had, sort of, managed a bridge forty millimetres long. Yes, the slight drooping tells me 40mm is too much, but what about 25mm? And can circular or semi-circular holes be printed without supports? I had a shot, and yes they can. They’re a little rough in places, but nothing collapsed.
While I was at it, I did another spool stand on a second 3D printer – a small, very cheap printer. The drooping turned into some loose stringing at the top of the cut-out, and I get the feeling it wasn’t far from totally collapsing, but it didn’t. A £90 3D printer managed a rough but workable print with an unsupported two-inch hole in the middle.
Finally I printed the inevitable 3D Benchy on the Ender 3, without supports. It came out just fine – the overhanging bow and complex wheelhouse showed no sign of collapsing (or even drooping) at all.
Sometimes you need supports when you’re using an FDM 3D printer; there’s no getting away from that. Even when they’re not essential, sometimes they’ll give you a better finish. Have I been overusing them, though? I suspect I have, and from now on I’ll be a lot bolder about eliminating them – and saving myself time, filament and electricity.