UDFT5152 Flush Trim Compression Cut Spiral Router Bit 1/2" D X 1-1/2" CL 1/2" SH 4-1/4" OLUse a bit that is very efficient at evacuating chips from the hole or the slot it is cutting. Up cut router bits are designed for deeper cuts while down cuts are better for shallow cuts. The upward direction of the flutes while rotating prevent debris from building up, binding, or even breaking the bit in those deeper cuts. The downward direction of the down cut flutes leave a cleaner edge than their up cut counterparts, but would bind on deeper cuts.