Printing Convex Overhangs

[RobH2]

To be honest I've never tried printing these features without support. I think its about time I print a few tests without support to dial in the optimal settings. I think a sphere is probably the worst case scenario so it'll be a good model to test with.

Thanks for the pics RobH2. After your second test finishes, if you could post what speed/ temp you're using, it would be much appreciated.

I used ABS at 230C and 30mm/s. The bed was set at 110C. I had two fans on it, one in front and one in back the whole time.

Wow... That came out much better than I would have expected!

I'll try one later today or tomorrow with the new code you sent. I have a 12-hour print to start right now. I did do a new test last night after my first one. I created some small supports to stabilize the sphere but the ones I created were still too small and they eventually broke loose. But I did get about 75% of the sphere. The first few layers did curl and get a bit fatter than the others like you speculated. It was interesting to see how faithfully the printer captured the facets of the sphere. The sphere didn't have enough geometry to make it smooth. I want to try to print a golf ball with dimples. That would be a good test.

Here are the photos from my second test last night. I had a jam last night and was able to mostly clear it without having to pull my head but I don't think it was totally clear when the print started. You can see the first few rings of the bottom of the sphere are messy. I think those would have been nicer if I hadn't had the jam. But, still, I got very good results.


y95-03.jpg y95-04.jpg

[Roxy]

It was interesting to see how faithfully the printer captured the facets of the sphere. The sphere didn't have enough geometry to make it smooth. I want to try to print a golf ball with dimples. That would be a good test.

The code at the bottom has the fineness of the sphere turned up so you will have a better approximation of the sphere. It will take a minute or two to compile.

y95-03.jpg y95-04.jpg

And adding that second sphere(r=20) command will save you a lot of plastic and print time. It will hollow out the sphere which will give you an extra data point. At the start of the print you will be trying to bridge out at almost 90 degrees and you will see how well you can do that on outer perimeters. Once you get up halfway, you will be trying to bridge out on inner perimeters. I have more problems with outer perimeters, but inner perimeters have their own set of issues. And that is why I cut a corner into the sphere. Corners cause me a lot of trouble on both inner and outer perimeters but in different ways. I suspect you are going to see a difference in behavior once you get past the half way mark.

z=83.75; difference() { sphere(r=25, $fn=100);
sphere(r=20);
translate([0,0,-30]) cube([40,40,60]);
translate([-20,-25,-z]) cube([60,60,60]);
}
translate([-25/2,-25/2,-(z-60+1)]) cube([25,25,1.1]);


If you want to see what the changes to the code do, take a look at the attached .STL