Chapter 59: In Which An Unreasonably Long Compass Is Deployed
I love hollow body instruments, but I do not love the hard corner where the top meets the side and digs into my forearm. The arch in an arched top goes part of the way to relieving that by elevating the plane of the strings away from the corner, but typically doesn't go far enough to serve the same function as a Fender-style forearm contour. You could arch it higher, but that would require carving away and wasting more and more material. Instead, I'm going to just bend the top.
This is a view from the tail end, showing how the top will follow a 16 inch radius across the width of the body. The back will arch across the bass side, providing a belly carve, while remaining flat on the treble side to leave the cavity high enough for the controls and battery box. (Pardon the visual mess, it's drawn on the back of scrap paper which shows through more in the photo than in person for some reason.)
The centre remains at almost full thickness across the string path leaving the central beams to carry the string tension load. Due to the wedge shape of the body, the sides will be nearly their original height toward the neck, while tapering down toward the bridge, with the bass side disappearing entirely at the corner. This might look cool or just really weird. We'll see.
I'm not sure this is really enough of an arch to accomplish the goal, but it's as much as will fit on the body without pushing the thickness past 50mm (2"). I had also sketched arching the top all the way to the back and leaving the back flat, but it just looked weird. So we'll go with this and see what happens.
To create the arched shape on the internal frame, the solution is of course a router jig. There are at least two ways to do it, either with the router [Invalid or Expired Link Removed] or
with the whole 'bridge' moving back and forth like this. For better or for worse, I decided to go with the second type.
So out comes the Unreasonably Long Compass and a quick-and-dirty circle routing jig to cut the bridge rails. I cut this in a few steps. To keep the rail from shifting away in the last cut, I plunged a little way in from the edge then came back and cut it flush later.
It's about 90% done at this point, just needing the box where the router sits to be permanently attached to the bridge. To minimize the length of the bridge rails, I've sized it to be able to cut from the centreline to one side. Then I'll flip it end-for-end to cut the other side.
You can't really see it in this picture, but the tops of the lengthwise rails have a 1/2" roundover so the bridge contacts a flattish surface instead of the 90 degree corners that the rails would otherwise have. That's probably not necessary for the amount of wear this is going to get, but it was easy enough to do.
One last step on the body before routing the arch will be adding lining at the side-to-top joint. I could do it afterwards and then trim it flush, but doing it at this point will help reinforce the sides for the upcoming routing job. When I was thinning down the body from my earlier mistake, the sides were vibrating pretty heavily as the router bit passed across their edges, causing some splintering in one location. Adding the lining now will help stiffen the sides, hopefully enough to make the vibration go away. If not, I'll hot glue some additional supports.
