spiral router bits and router technique

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?
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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.
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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
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BillyBob wrote:

Wouldn't burn affect glue adhesion?
-Chris
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I just get some burning at the very ends of the mortises. I don't worry about it, whether it affects gluing or not.
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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
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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

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