> Would it help if I scaled up when creating the knurl - before I get to any of the cutting?

So, to answer your question - no I don't think that this would help since the main difficulty is more about grazing conditions between the cutting surface and the edges of the knurls.

Grazing conditions make for a lot more difficulty in getting a clean intersection - in general when things punch more clearly through each other rather than grazing along each other for some shared area it is easier to generate clean intersections.

In your case here, I know it looks like you've got the cutting surface punching clearly through the object, but remember your object is not just a cylinder even though it has that general shape, you've got a lot of little edges on the knurl pieces and when some of those edges come very close to aligning with the direction of the cutting surface it causes a grazing situation where the edge skims over some common surface area with the cutting object rather than the cutting object dividing the edge neatly into 2 pieces.

- Michael