Hi Dave,

That used to happen to me a lot. Slot milling over 8mm risks poor chip evacuation and clogging of the tool. I've seen people machine the outside material completely away (i.e. an outer pocket to leave the central island, not a perimeter slot). But then you need to be able to hold the part in the middle which isn't always possible.

Another option is to use something like adaptive machining to mill a larger width slot than the tool.

I tend to reduce the DOC when over 8mm into a slot and that works OK. I vacuum out the slot on every pass and give a quick spray of WD40.