Custom Pickguard

My J Bass kit won't be coming in until May, but I thought I would get started on planning the custom pickguard.

How would one go about getting the nice square edges of a P bass pickup cutout using a standard router? I have a template already, but looking at my bit choices, it seems like I could only get rounded corners with an 1/4" bit and I would have to maybe use a razor blade to clean it up (not ideal). I might try a 1/8" bit, but it's going to take some modifications to my template.

Does anyone have any tips?

You could make a template or use another pickguard as one, rout the main hole and use a file with a square edge in the corners

I've done a fair bit of pickguard customisation over the past couple of months - and I have to say it's my least favourite part of building! I've been using a hand-held dremel (no router attachment) and taking it very very slowly and carefully to cut away the large areas, then switching to files to finish it. On the long flat lines a large fine toothed file is good, and for the corners I've been using a set of small jewellers files. It's slow work but you can get a good result. I know others use a router as stan says and I may look at one in the future. Getting a consistent bevel around the edges is also a challenge that I'm sure the right router bit would solve but I've been going at it with the files too. Sorry to not have an easy magic solution! I hope, for your and my sake, others might!!