Routing a wider pickup cavity without chipping the finish

[MatrixClaw]

Hey guys,

Just a hobbiest woodworker here - I've routed a cavity wider on a guitar with an oiled finish and had no issues, but never on a painted guitar. I'm fixing up an old Squier for my daughter for her birthday and need the cavity slightly wider for full sized pots. I have some ideas on how to do this without wrecking the finish but am curious what someone with more experience would suggest?

Any advice would be greatly appreciated!

 

[poolshark]

With a thick, relatively pliable finish like the polyester on your Squier, a good router and any reasonably sharp bit should be able to cut without chipping. To put it in perspective, Warmoth cuts a lot of cavities post-finish. You could try some masking tape over the surface if you really want to be sure, but I’d bet you’ll be fine either way.

 

[Jack Daniels]

I use tape on the surface, but the real trick is to take the very first cut shallow. As in just barely through the finish with a sharp bit. This can be tricky if you use a long bit or a shallow set of templates. I have a 1/2" bit that has only a 1/4" of blade height that I use. With the template and bearings in place, my first cut is about 1/16" deep.

Then take your time going deeper (never more than about half the diameter of the bit at a time. IE: 1/2" bit, go 1/4" deep). This keeps the bit from Chattering. Its the chattering that does the most tearout of wood and finish etc.

 

[MatrixClaw]

With a thick, relatively pliable finish like the polyester on your Squier, a good router and any reasonably sharp bit should be able to cut without chipping. To put it in perspective, Warmoth cuts a lot of cavities post-finish. You could try some masking tape over the surface if you really want to be sure, but I’d bet you’ll be fine either way.

Interesting! Good to know, I'm not super worried about a little bit of chipping since the pickguard should cover it, but the finish does seem pretty thin, so hopefully it'll be an easy job, then!

I use tape on the surface, but the real trick is to take the very first cut shallow. As in just barely through the finish with a sharp bit. This can be tricky if you use a long bit or a shallow set of templates. I have a 1/2" bit that has only a 1/4" of blade height that I use. With the template and bearings in place, my first cut is about 1/16" deep.

Then take your time going deeper (never more than about half the diameter of the bit at a time. IE: 1/2" bit, go 1/4" deep). This keeps the bit from Chattering. Its the chattering that does the most tearout of wood and finish etc.

Yeah, I was just going to tape it but wasn't sure if I should clamp a thin piece of wood to it just in case to help, sounds like I should be good. I'll go slow and do small passes at a time, then. Thanks!

 

[Khromo]

When I used to install Badass bridges I used to very carefully scribe around the profile of the proposed cavity with an exacto, going very slowly, until I had pretty much cut through the finish. I took a lot of passes with very light pressure.

Working on more brittle finishes this could be a life saver, since you had to do the corners with a chisel!

 

[MatrixClaw]

When I used to install Badass bridges I used to very carefully scribe around the profile of the proposed cavity with an exacto, going very slowly, until I had pretty much cut through the finish. I took a lot of passes with very light pressure.

Working on more brittle finishes this could be a life saver, since you had to do the corners with a chisel!

Hmm, that's not a bad idea at all! Thanks for the tip!

 

[Alan Wolf]

If you needed to buy a bit to do this, one that has downward spiral (so that debris is pushed down, rather than lifted out) helps to prevent edge tear out.