I was asked to do a quick and dirty cavity mod for a client who wants to swap the pickup positions on his P-bass. His remarks were to make it usable, and don't worry about a fancy clean cavity - it gets covered with a pickguard for goodness sake
So, should you ever decide to do this mod yourself, here's how I do it (althought usually much, much tidier)
The first step is to lay out where the cavity needs to be expanded. I usually like to make one large cavity in a case like this, providing the option for the owner to swap out to a regular P pickup orientation in the future - this client preferred to have ears for some additional support
Once I know where I'll be cutting, I then step to the drill press to rough things out. I first drill out the ear tabs utilizing a Forstner bit
and then I follow-up by removing the remainder of the cavity area
After things are roughed out, I utilize a routing template and pattern bit to clean things up
Definitely not the cleanest route I've ever done, but it's functional and will work fine when the pickguard is placed
After all the routing is completed and the cavity has a uniform 5/8" depth I paint it with three coats of shielding paint, letting it cure 24 hours between coats. Once it's all cured I'll assemble this bass back together and get it back to the client.
Total working time on this mod, not counting major disassembly: 45 minutes
all the best,
R