I have created solid object using the sweep command. It is the winding, rectangular-cross-section thingy in the drawing. I then created a cylinder using extrude. I want to subtract the cylinder from the thingy but when I do, it takes out the cylinder and the entire left side of the thingy. I don't know why. How can I get it to just take out the cylindrical portion of the thingy but leave the rest of both sides?
Thanks,
Mark

Hi Mark, if you re-load the file you just posted and try it again it seems to be working better now. There are a few cases where saving and reloading the file corrects some problem in the geometry.

But there's still a problem - you don't really have a clean intersection here, you can kind of see in this area here how the objects are just kind of barely skimming through each other:



You can kind of see there that the cylinder and the sweep have some parts where the cylinder is just barely sticking to the outside, and then other regions right nearby it where the sweep is actually the part that is sticking the most to the outside.

An inexact coincidence like that is very difficult for the booleans to resolve correctly, they may try to do something like make numerous intersection curves in that region and try to slice things up into really super thin slices with irregular boundaries, stuff like that.

You can have things that are coincident like that in booleans, but only when they are more exactly on top of each other instead of partially weaving in and out from one another like you've got here.

So to get a good result, you'll need to do something different to not get such a indeterminate and "paper thin" intersection zone like that, either have the cylinder recessed some more or punching all the way through some more.

- Michael

Micheal,
If I change the curve so that it is completely flat across the back of the cylinder before it curves away, will that work? If I can, I would like the cylindrical cut to be flat against the back of the curve.

Hi Mark, it's not quite clear to me what result you want - do you want to be a hole in the sweep left by the cylinder, but with a sharp notch left on one side, instead of it being cut all the way through the whole sweep?

One other issue you may be running into is that your pieces are getting to be fairly small in size, like that cylinder has a radius of 0.08 units.

Things may behave better if you scale up by 10 times instead of working at a smaller scale like that.

In the attached 3DM file I have adjusted things slightly.

I moved the cylinder slightly in this direction:



Which then makes for a cleaner non-skimming intersection.

Then I also scaled up by 10 times, and then the boolean produces this result:



- Michael

You may also want to do something like slice your sweep up into 2 pieces by drawing in a dividing line through the middle of that cylinder and using Boolean difference using the line as the cutter.

Then you may be able to work on each half of the sweep with some slightly different adjustments, like make the cylinder go all the way through the sweep on one side, but keep it in the notched position on the other half where it is not skimming.

- Michael