spiral router bits and router technique

[Doug]

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?

[Leon]

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.

[BillyBob]

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.

Bob

[TheNewGuy]

Wouldn't burn affect glue adhesion?

-Chris

[TWS]

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.

TWS

[bluemax1811-newsgroups]

I just get some burning at the very ends of the mortises. I don't worry about it, whether it affects gluing or not.

[max]

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