Why does Simplify3D want to start a circle in mid-air?

[deonb]

I guess the picture tells it all - this is a cavity for a nut, and all goes well until it hits the layer just above it. The sides are printed correctly in one piece as a bridge, and then it starts with the screw-hole again, but it starts in mid-air.

Needless to say this doesn't work:
https://www.dropbox.com/s/oay1imi0vvuio ... y.png?dl=0

Is there a "obey gravity" setting or something that I'm missing perhaps?

This is using the standard TAZ 5 profile on medium, except with the Nozzle Diameter changed to 0.5

[dkightley]

There is not an "obey gravity" setting that is missing......your part obviously needs some support to ensure it prints correctly. And with the decision to include/exclude support in the hands of the user, the software does as it is told....even if the print will ultimately fail!

Bridging will only work where there is a straight and uninterrupted line between the supporting part at either end of the free space. Where you have an edge....like you have ....then bridging is not possible, and the printer will print whether or not there's any support.

[deonb]

There is not an "obey gravity" setting that is missing......your part obviously needs some support to ensure it prints correctly. And with the decision to include/exclude support in the hands of the user, the software does as it is told....even if the print will ultimately fail!

Bridging will only work where there is a straight and uninterrupted line between the supporting part at either end of the free space. Where you have an edge....like you have ....then bridging is not possible, and the printer will print whether or not there's any support.

Ok, but this is again one of those cases where Cura does the correct thing - it bridges the sides before starting to print the outline of the hole. It can do this part without any supports required (repeatedly so).

If Simplify3D just started printing the outline of that hole over a side instead of in mid-air it would already work better.

[horst.w]

...

Ok, but this is again one of those cases where Cura does the correct thing - it bridges the sides before starting to print the outline of the hole. It can do this part without any supports required (repeatedly so).

If Simplify3D just started printing the outline of that hole over a side instead of in mid-air it would already work better.

About this I'm not very sure!

I had to print today a small cylinder with a hole in the bottom for a nut.
For testing your statement I have turned the bottom of the cylinder to top. You are right, S3D does print the (new) top layers in the plain air. Without support it is not possible to print this object as Doug has written.

But Cura (the last red pic, importe Cura-GCode in S3D) has an other very grave fault - it forgets to print the complete hole and fills up the space with infill. That cannot be the solution.

[dkightley]

At least its comforting to hear that S3D is not the only software with undesirable features!

[moggie]

I purchased s3d yesterday to test it out, and a hollow cube without support was the first thing I tried as I wanted to see how forgiving the material could be so that I could consider this in future designs. Reviewing the layers before printing I found the same issue as you, layers in mid air. If the slicer had sliced horizontally between the existing sides of the cube when reaching the top, the 25mm or so open span would have barely sagged at all and printed ok. I let it print anyway, and even with the faulty slicing the front and back sections were almost perfect, but the sides much less so (the saggy bits in the photos and other detritis that isn't visible), which was inevitable for the way the slicing infill worked out.

Would be great if the slicer could handle this, and/or give the user the option to adjust slicing over a specifc set of layers plus the ability to add and remove tool paths because successful unsupported regions within reason are totally possible.

[CompoundCarl]

Moggie - I've printed that cube many times before and never had any issues with how the software sliced it. Can you post your factory file (File > Save Factory File)?

[moggie]

Sure. See attached zip with the freecad source, stl files and factory file for the second cube. I made two cubes, the second with a top without being inset internally. The images reveal the middle skirt created in mid-air, and on the second image, the infill was ok for the top front and back, but not suitable for the sides so that the outer layer didn't adhere. The top sides did form with subsequent layers, but had the first layer all curled up and stuck to them makng a cleanup difficult. I also tried different infill percentages and algorithms.

[CompoundCarl]

Honestly, I'm not sure how you would print that any better.. I think you need support material to get good results with that one. It isn't suitable for bridging, since there is nothing to bridge between on all of the inside perimeters.

[coolbloke1324]

The cube can definitely be printed without supports. It seems obvious to me. You bridge from one side to the other, then bridge from another side to the existing bridge.

Same goes for circles in mid-air. Bridge the edges of a square first, then print the circular section using the bridged square as "support" for the circular section. Circles are obviously going to be more difficult but it's still possible without printing completely mid-air.