They make up cut and down cut spiral bits. Up cut will clear a blind mortise
of chips, down cut will move the chips in to the hole. Each has it's own
uses. A downcut will work well trimming veneer on the top of the board you
are cutting, an upcut works well when you are routing on the back of a piece
and the finished surface is on the other side. I think the burning is from
the too large a feed. I would rough out the hole with something else and
finish with the spiral bit.
max


I'm making a bunch of mortises in oak and burnt out a straight bit in
the process. Picked up a Freud 1/4" spiral bit that's supposed to
clear material more easily and be good for such applications??
However, I am finding that I'm getting a lot of burn, easily. I slowed
down the router speed and took very small passes, and this improved the
situation somewhat, but I still have to proceed slowly. Is this to be
expected with these bits? Am I doing something wrong?