I'm planning to put new tuners on the Regal tenor. So I figured I'd go ahead and enlarge the old tuner holes while the neck was still off the guitar.
There was some sort of white powdery material inside the holes. You can see it in the picture. I'm not sure what it is, but the drill just went right through it.
You can see remnants of that white stuff. It may have been glue.
You may recall we measured the top deflection at the bridge (the amount the top went down - deflected - after after removing the strings, relieving the tension) at a whopping .019 of an inch (maybe .45mm).
When I went to jack the top up to compensate for that .019", I found that the jack was pushing the top and the back out.
To prevent the back from moving out, I clamped a piece of birch plywood onto the guitar.
With the back held down, only the top can move now.
Then we raise the jack it up .019 inch, and measure it with our deflection gauge.
Now we have the top set to where it would be if it had strings on it. We're compensating that amount so when we look at the neck set, it should be more accurate.
This will give us the amount of material to remove from the bottom of the heel to set (or pitch) the neck to the correct angle. That amount is removed from the bottom, and gradually less is removed as we go up the heel, until nothing is removed where the heel joins the fingerboard. This should be clearer when you see the cut line on the heel.
We need three measurements: 1) the 'difference' that a straightedge laid on the frets parallel to the strings falls below the top plane of the bridge; 2) measurement "A," the distance from the center of the saddle slot to the point where the neck joins the body, and 3) measurement "B," the height of the heel. Note that "B" is NOT the depth of the body at the heel - it's the height of the heel itself, which may be different than the depth of the body.
The formula, which is on the sheet also (click for a larger view), is the difference times B, divided by A.
If you follow my calculations, you'll see how I came up with .024 inches to take off the bottom of the heel.
Of course, the formula would work using metric measurements (and probably be easier to work with).
I didn't create this formula - I'm nowhere near that smart. I originally learned it from Dan Erlewine's guitar repair book. It's also on his neck reset DVD, which I highly recommend if you're contemplating doing a reset yourself.
I set my trusty Starrett dial caliper to .024" so I can mark that measurement on the bottom of the neck heel.
That green arrow in the picture shows how wide .024" is on the caliper jaws. It's really small. Almost tiny, in fact.
In the picture, you can see how the point at the bottom of the heel (arrow) is .024" and that the line goes up the heel, the space getting smaller, until it's zero at the fingerboard. That's the triangular-shaped slice we'll remove from each side of the heel and from the bottom.
The neck will then be angled up that amount, which will give it the correct set. It's geometry, actually.
You can see there really isn't much to take off. Just that small amount will correct the neck angle. We need to be careful not to take too much off...we've all been there.
This is where you really need high-quality chisels that are sharp. This is a precision cut for sure. Your hardware-store chisels really won't...ahem...cut it.
It's a paint stick which has been turned into a sanding stick. One side has 220 grit paper, the other has 320 grit. I use 3M '77' spray adhesive for a temporary bond. When the paper wears out, take it off and glue a new piece on.
I generally do a few strokes, then fit the neck on the guitar and check the set. We check the set the same way we did way back at the beginning - with a straightedge laid on the frets.
Remember: you can take wood off, but you can't put it back on! Your line should be accurate, but you can't blindly rely on it. We're working with such a small amount to remove that just a few strokes of the sandpaper will do it.
Only the outside edges of the heel need to touch the body of the guitar, and their angle will determine the set of the neck.
The neck itself will be held in place to the body of the guitar by the dovetail. The sides of the neck don't hold the neck on; again, they just (a big just...) determine the neck angle.
The process is: sand some material off, then test fit onto the guitar to check the set of the neck. Then sand again if necessary. I did 3 sand-and-test rounds this time.
The bridge is held on to the guitar with double-stick tape.
That set looks good! Right at the top of the bridge.
The dovetail is very loose at this point. Don't panic! This is normal - we've changed the relationship between the dovetail and the neck block.
To make the dovetail tight, we'll need to glue some shims onto it and adjust the fit.