Straight and spiral carbide bits can be honed on the flat inside face with a fine diamond card, which restores a surprising amount of edge. Profiled bits need a proper grinder and a service — honing a profile by hand changes its shape.
Most router bits people throw away are dull rather than damaged, and dull is partly recoverable at the bench.
What you can do yourself
On a straight bit, the cutting edge is formed where the flat face meets the relief behind it. Lay a fine diamond card flat against that inside face and stroke it a few times, equally on every flute. You are not reshaping anything — you are removing the rounded-over edge. Count the strokes and give each flute the same number, or you unbalance the bit.
Never touch the outside of the cutter. That is the diameter and the relief, and altering it changes the size of the cut and can remove the clearance that stops the bit rubbing.
What you cannot
Anything with a profile: ovolos, coves, rebate bits with shaped edges, panel raisers. The profile is the product, and a hand-held stone destroys it. Those go to a sharpening service with a profile grinder, and on a large bit that is worth doing.
Before you sharpen anything
Clean it. Resin on carbide behaves exactly like a blunt edge, and a soak in resin remover with a brass brush recovers a lot of bits.
The one to check first
The guide bearing. A seized bearing burns the edge it rides on and is a cheap replacement.
Last reviewed 2026-08-12