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?
You want the bit to move at a pace that will keep it from heating up the
wood and burning it. This often requires shallow passes but not necessarily
a slower spin speed with a bit that small. Secondly a 1/4" bit will heat up
much more quickly than a larger bit. You might also consider using a single
flute carbide bit . You should be making relative shallow mortises with a
bit that small.
I think burn is a fact of life when cutting mortises with a router. I never
worried about it because its going to be inside the joint anyway. Its an
obvious question, but I assume you got a spiral bit that spirals to pull the
shavings up. How small are your cuts? I usually cut about 1/16" at each
pass. Actually I just set the depth near the final depth I want to cut and
then move back and forth with light pressure on the top of the router. It
cuts lightly in each direction when I do that. I've never used a 1/4" bit
for mortises. I was doing larger stuff with a half inch bit. I used a
straight bit and had no problem, but my router has built-in dust collection
that is very effective for this application.
If you drill out the inside of the mortise to remove the excess your
router bit will just be working on the outside edge of the mortise and
your router bit won't get so hot. It is a problem if the bit is
completely surrounded - it won't have a chance to cool.
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.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.