Remnants after boole cut is made.

 From:  Michael Gibson
3217.3 In reply to 3217.1 
Hi Leonard, so your profile for your sweep is quite small in size, you may want to scale all this stuff up by 10 times so that you are not working on sweeping such a small object that is getting close to the 0.001 fitting tolerance.

But that does not seem to actually be the main cause of your problem - it seems that your threads you created actually runs into itself:

The booleans cannot process objects that have pieces of their surfaces running into themselves, I think you need to have some more space there so that you don't create that kind of self-intersecting object in order for the booleans to work properly.

- Michael