How can a table saw cut a curve? Dan Erlewine has a neat tip and a jig you can make in your shop. The result is a precisely curved truss rod channel just like the one in an original Gibson neck.
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00:00Today, I'm installing a truss rod access hole in this Gibson-style neck.
00:14It's as easy as that, and it didn't take long, did it?
00:18Something I'd like to show you is my slot in here is curved.
00:23It's not a straight flat-bottom slot.
00:25I cut it on a curve.
00:27I can show you that exact curve on this cut-in-half Gibson neck.
00:31The reason you want a curved truss rod slot is because when the neck pulls up, which they
00:35do, you string up a guitar neck and it pulls up over the years and you get high action,
00:40you tighten that curved rod and it comes back down again.
00:43The first thing we'll need for making a curved channel are the measurements off this Gibson
00:48curve.
00:49This little point sticking into that glue line, that's where I measured from.
00:53That's the joint between the mahogany and the rosewood board.
00:56The deepest part was at the seventh fret.
00:59As I went down, it got shallower, and that gave me the basic depths all along the curve,
01:04which I was able to copy.
01:06I took all these measurements and I transferred them to a stick, connected the dots like that.
01:13I sawed this out and got my curve.
01:17Now this is just a template for making a jig to go on my table saw.
01:22A table saw is made for cutting straight lines, and if you cut a truss rod channel like this,
01:26it will be straight, not curved.
01:29But if you add a curved piece of wood to the table saw, you'd get this jig.
01:35The secret is to put a shim on the beginning and the end of your neck block so it will
01:39raise up as it comes onto the curve and cut shallower, and as it passes over the blade
01:45onto the other side, it's cutting the deepest part of your channel.
01:50Then as the other end with its shim comes over the curve, it starts to raise it back
01:54out again, and the result is a curved channel.
01:58So let's make that jig.
02:01This is a piece of 2x4 Douglas fir, and I have my template, curved side down, flat side
02:07right flush with that board, and I'm just going to draw that out.
02:13This is my arc.
02:17And I keep moving the arc along.
02:22Now there's a long curve, but cut off on the bandsaw.
02:37Okay, here's my long curved board.
02:40I'm going to pull out this throat and fasten it to the bottom of the board.
02:46That's how I mounted it.
02:49Now I'm going to cut right up through it with the saw blade.
03:03The next step is to put little shims at each end that raise it up off the curve as you
03:08cut.
03:09I'm going to superglue these shims down.
03:12They pop right off with a chisel.
03:15Set that there.
03:17Let that dry a second, and I can make a cut.
03:21Wish me luck.
03:31The teeth aren't that wide, so I'll make three cuts, one right on the center, one I'll move
03:36the fence over a little bit, it won't take much, like a 30 second, then I'll move it
03:41back the other side, and I'll get a 3-16ths slot.
03:56That's it.
04:01So, there we have it.
04:04We have a professional slot cut right through this mahogany blank for a Gibson style 3-16ths
04:11diameter truss rod, and it's got a curved bottom, and it's very cool.