Why Are My Mortising Cuts Leaving Burn Marks?
Issue: Issue 316
Posted Date: 12/18/2012
When I try to mortise a 3/8 or 1/2 inch x 1/2 or more inch deep, I burn and ruin my bit. I have tried different speeds but no luck. I am using a Bosch router with a Kreg lift. What is my problem? I would appreciate any help that you can give me. Thank You -- Earl Purcell
Chris Marshall: Earl, if you are starting with a clean, new bit and you are still getting excessive burning, one possibility is that you are mortising wood with a high resin content like pine or cedar. Or maybe it's a species that's just prone to burning, like cherry. Try mortising some oak or maple and see if you get better results. A 3/8- or 1/2-in.-deep mortise is also too deep to make in a single plunging and feeding pass. Make sure you hog out the waste in stages no deeper than about 1/8- to 1/4-in. with each pass. Otherwise, routing out too much waste material at once is hard on the bit and router. Things heat up as the bit slows down, and burning is the result. On the other hand, if you are having bad results with the same bit, it might simply be dull. Buy a new carbide bit and try again. Hope these suggestions help!