What’s Causing This Forstner Bit to Burn?

This woodworker is using a carbide forstner bit and having trouble with the speed. He’s getting burning if he runs it faster than 600 rpm (on pine) and chipping if he runs it slower. What’s up?

Simon Watts:¬†Forstner bits are notorious for this: the cylindrical cutter head is not relieved, so it tends to heat up because of friction with the wood. I’d suggest experimenting with different rates of feed. Usually, the faster the feed, the rougher the cut but the less heat generated. Try to find the best balance.

Rob Johnstone: While Forstner bits are wonderful for boring large diameter flat bottomed holes and drilling accurately at an angle, they are really fairly complicated cutters. However, the problem discribed seems to simply be a dull bit. Carbide cutters stay sharp longer, but in my experience, do not take as keen an edge as high speed steel. Once dull, a carbide bit burns and chips with the best (or worst) of them.

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