I mentioned in the last post that after removing wood from the sides of the neck heel to get the set correct, the fit of the dovetail was now loose.
Hopefully you can see in this picture just how much of a gap there is between the male and female parts of the joint. The blue arrow points to the big space there.
I'd guess it's about 3 to 4mm. You can wiggle the neck side to side in the joint, and it won't stay in place at all - it just falls backward.
This isn't unusual on a neck reset. It's a bit larger than usual on this particular instrument, since the original dovetail wasn't cut too well.
However, it's relatively easy to fix.
What we're going to do is fit some shims on each side of the dovetail and trim them so the joint will be tight.
If you look closely you can see the Hatch Green Chile Salsa jar I'm using for this batch of hide glue. Good stuff. (The chiles...well, the glue also).
You can see one of the shims has a sort of angle at the top. This was not by design. The scrap of maple I made these from was an odd size. Not a big thing.
The sides are tapered to fit the taper on the dovetail and sit square in a vise.
I have a bit of waxed paper over the joint so the glue squeeze out won't stick to the cauls.
The vise, by the way, comes with unfinished jaws. I didn't like the idea or the look of unfinished wood, so I put about 12 coats of Tru-Oil on them. Every time I use Tru-Oil, I'll just give them a little wipe to get even more on them.
I think I need to start a second storage box. This one is overflowing!
Stick a piece of carbon paper over the dovetail and press it down into the joint.
Note how high the neck is sitting up in the joint at the beginning - probably about 1/4 inch, or maybe 7 or 8mm.
I suggest you cut up a bunch of carbon paper, since you'll go through a number of pieces.
I use a scraper to scrape those marks. There will be marks on both sides, as well as the front and bottom as you progress.
Then repeat the process until the neck sits further down into the joint.
I may have made my shims too thick, but I'd rather start with thicker shims and work my way down.
I had probably done over 20 passes of fit, scrape, fit, scrape at this point. When you feel like it's taking forever and you may lose your mind, stop and take a break and begin the next day.
This isn't a race and we want to be accurate.
So I put some thinner shims on the body side of the joint to compensate.
The neck is straight and it's super close to being perfectly fitted!
That tiny gap at the top will close up when I clamp it down to glue it.
At this point, the dovetail is very tight and takes a bit of effort to get apart. This is exactly what we want. The joint should be tight enough that it stays together under tension. You don't want to rely on glue to hold it together. The joint should just have a small amount of glue on the sides to keep it in place.
When you take an old untouched Martin apart, you'll see how accurately cut the dovetail is, you'll rarely, if ever, see shims, and you'll see very little glue. Of course, you will likely need shims on a reset, but you should be working to get a good-fitting joint that doesn't have to rely on a lot of glue.
If your dovetail fits together easily and won't stay in place on its own, you'll need to shim it so it takes a bit of pressure to fit, and then will stay in place and take some effort to take apart.
Next, I'll clean up that gap between the heel and the body of the guitar, clamp the neck into place and test the neck angle before gluing it up.