Wow, great tutorial Edwin!

@Lish - that definitely looks like a bug but unfortunately a difficult one to fix.

There is a very small mis-alignment between the closing seam of your cutting object and the closing seam of the base object. MoI is getting confused when trying to process this area with nearly overlapping edges.

If you take your cutting object and rotate it by 90 degrees, then that moves these edges away from one another so they aren't overlapping anymore and then your boolean will work.

- Michael