Advice for Routing Cavities on a Finished Body

[nervous]

I have two smallish routing projects I plan to embark on over the next 2-3 weeks. A battery box in a bass and a third pickup on a guitar. Both are on factory painted bodies. I have everything I need from tools to new, sharp bits to templates but the one thing I can't find a consistent answer on is for techniques to insure that I don't have any finish chipping or damage along the finished edges when complete. I had a J Pickup rout 'professionally' done in a P Bass body a couple years ago and and wasn't thrilled with the edges. Not so noticeable in use but not quite the finishing I'd hoped for, especially at the cost. I have read that scoring finish the perimeter of the cavity with a razor knife is one method. Another free-handed the straight lines with a Dremel cut off wheel. Both of my current jobs have some small margin of error as the battery box has a lip and the pickup will have a pickup ring. But not so much that a larger chip wouldn't be catastrophic.

What tips or techniques can you offer that you use to avoid edge finish chip out when routing a finished body?

 

[Beej]

I typically score along the lines of the rout with an exacto blade a few times to ensure it cuts into the finish. Then i tape it off and rout. So far, knock on wood, I've not had any chips or breakouts. I've done this on polyurethane, polyester and nitro finishes.

 

[nervous]

I typically score along the lines of the rout with an exacto blade a few times to ensure it cuts into the finish. Then i tape it off and rout. So far, knock on wood, I've not had any chips or breakouts. I've done this on polyurethane, polyester and nitro finishes.

Thank you. This seems to be the method I will use. Am I looking to cut through teh finish or simply significantly score the finish on the perimeter? I'm thinking teh scoring will create enough of a weak spot/break point in the finish to be just fine.