Tips & Tricks: Shop-made bottoming bit

Shop-made bottoming bit

I turn a lot of small, lidded boxes. One of the challenges is shaping the end grain surface at the bottom of the cavity. To make this onerous task easier, I make my own bottoming scrapers by grinding spade bits to conform to the shape I want. Start with a bit that matches or is a little bigger than the inside diameter of your box. Grind off the tip, then shape the bit as shown. I find performance is best if the cutting edge has a negative rake, so grind the underside to a 45° bevel and the topside to 25°. To use the bit, first drill out the bulk of the waste with a Forstner bit chucked in a tailstock-mounted drill chuck. Then swap that bit out for the bottoming bit and finish the cavity, eliminating the dimple from the Forstner bit and rounding the outer corner. As you cut, advance the bit slowly—otherwise it may chatter and overheat. 

—Jeff Peters,
Redgranite, Wisconsin
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