Most (but not all) aluminum rims offer sharp hole edges to nipples. If the rim hole is not chamfered that edge can carve into a nipple, through its protective coating. Corrosion loves to exploit this situation. One technique that can help is carefully chamfering sharp nipple holes.
Use a multi-flute chamfering tool with a 90º angle to match the nipple contour. It takes only very light hand pressure. This is not countersinking like is done for flathead screws. You just want to knock off the sharp edge. If the chamfering makes a too-deep shape your nipple loses its ability to align to the spoke incoming angle.
Our bit is nitride coated, 6mm diameter, 90º angle, 5 flute, and 1/4" hex drive. You can use it barehanded or with a holder. Remember, very little pressure!
