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