Aïe : I have swept a rectangle along a helix and wanted to chamfer just the 4 "long" borders, but not the two faces.

I could have chamfered the rectangle before sweeping, but for the sake of understanding, can someone help me out with the correct way?

Attached file has the solid after the sweep of the rectangle on the left, and my unfortunate chamfer on the right. I don't understand why MoI is doing what it's doing (on the right).

TIA,
Ditto

Hi Ditto - that result is from some bug in the filleting engine where it couldn't figure out how to cut the ends of the chamfer pieces off. I'm not sure why in this case that failed, since it seems to be a pretty simple intersection with the end faces there.

When a fillet or chamfer had some error in its calculation, MoI will try to still spit out all the surfaces that were able to be calculated, with the hope that you may be able to salvage the result with some manual steps.

In this case it is possible to finish the model from the fragments you have there - to do that select all the pieces on the right-side object there, there are 5 pieces there the main body piece plus the 4 chamfer surfaces, select all 5 of those pieces. Then run the Construct > Boolean > Merge command.

That will then slice the solid with the chamfer surfaces, cutting it up into 5 pieces - select the 4 corner pieces and delete them and you'll be left with the chamfered result that you were trying to get.

I'll put this on my list of test cases to try and examine in the future to see if I can figure out what the bug is in the fillet system that is making the trimming part to fail.

- Michael