Crawls Backward (When Alarmed)

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Gluing Acoustic Guitar Neck to Body - Regal Tenor Neck Reset Continues

In the last post I mentioned that I'll clean up the gap in the joint between the neck heel and the body of the guitar.

The way to do this is with a narrow piece of sandpaper.  In the past, I've cut strips from a regular sheet of paper.  Which works fine, but the paper tears easily.  So this time I'm using cloth-backed 120 grit paper, which is pretty tough and doesn't tear.

Hold the neck down to the guitar and pull the paper through.  It really just takes a few pulls and the heel will assume the shape of the body.

Here's one side.  Looks pretty good.

The other side looks the same.

This is where having a good fit on the dovetail pays off.

I restrung the guitar and brought it up to pitch - in this case it's CGDA tenor tuning.

The dovetail will stay in place so you can tune the guitar.  If you whack the joint, yes, it will come apart.

I did this to check the set.  As you can see, it's really close.

I probably could have left it, but I went ahead and took a touch (.011") off the heel so it lined up perfectly.

I forgot to take pictures of the re-re-test.  Sorry.

Now to reglue the neck on the guitar.

I scraped the surface under the fingerboard extension to get a 'fresh' wood surface for the glue to adhere to, and I did the same on the guitar body where the extension will be glued down.

I have this rectangular caul which is ideal to put inside the body parallel to the brace that runs just above the soundhole.  I'll use that as a spot to clamp the fingerboard extension down...that will be clearer in a minute.

I don't always heat up the mating parts, but in this case, where the areas to be glued are fairly large, I do heat them up.

Just a regular heat gun pointed at the dovetail and fingerboard extension area enough to warm them up and give a little more working time for the hide glue.  The glue is heated to about 140°F (60°C), and begins to gel at about 90°F (32.2°C), so we have a couple minutes maximum to work with.

Brush the glue onto the body, and just on the sides of the dovetail.  We don't need glue on the 'cheeks' of the neck.  Only those sides of the mating parts of the dovetail.

We put the neck into place and clamp it down.

I had all of my cauls and clamps ready to go.  I do a dry run without glue so I can get the clamps adjusted closely to where they'll need to be to save time once the glue is applied.

The caul I showed above is inside the body and the two c-clamps are attached between it and a second caul on the fingerboard extension.   You may be able to see that the fingerboard extension caul has 'fret slots' cut out of it.  It's not critical, but does help get some clamping pressure right on the board rather than the frets. 

Then a bar clamp on that same fingerboard caul and a third caul under the heel/body joint.

There is some glue-squeeze out of the fingerboard-to-body joint, and I get most of that now before it sets.


Guitar Neck Reset Continues - Shimming the Dovetail on the Regal Tenor

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.

I used some scrap maple and sanded it down on the ROSS to about 0.90 of an inch or so. You can see the test-fit on the dovetail in the picture.

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).

Now we just brush some glue onto the sides of the dovetail.

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.

We put the shims on the dovetail and grab the cauls to clamp them up with.

Here are our Crawfish Instruments™ custom dovetail shim gluing cauls.

The sides are tapered to fit the taper on the dovetail and sit square in a vise.

Here they are in use in the wonderful guitar 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.

This is my box o'cauls. Some are purpose-made for specific jobs, and some are just random hunks of wood to use for protecting guitar bodies or necks from metal clamps.

I think I need to start a second storage box. This one is overflowing!

Now the tedious fun part of the job begins.

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.

The paper highlights where the shims are contacting the female (guitar body) part of the dovetail.

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.

After a number of passes, the joint has closed down to just a couple of millimeters.

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.

As the neck got further down and the fit got better, I noticed it was not straight - perpendicular - to the body of the guitar. It was angled toward the bass side of the body by a couple millimeters.

So I put some thinner shims on the body side of the joint to compensate.

Now we're there.

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.


Neck Reset on Regal Tenor Guitar

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.

I used a 3/8 inch Forstner bit on the drill press to enlarge them.

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.

The holes after being opened up.

You can see remnants of that white stuff. It may have been glue.

Now on to The Main Event.

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.

You can see the magnet for locating the jack, as well as the ratchet to raise the jack inside 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.

On the left is the drawing I did for the neck set calculation.

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.

Next we take our measurement and lay it out on the guitar.

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.

I've used tape in the past to lay out the line, but it's not that accurate. This time I marked the cut line by scratching a chisel on the heel.

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.

Here's the mark laid out on the heel. I used a corner of the chisel to scratch the line on the wood. This is better than tape, because I was able to follow the ruler exactly with the chisel. Plus we have a mark that can't shift like tape.

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.

I like to shave the end cap down to the line as a reference point. I think you may be able to see the line in the picture - I'm almost 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.
Here's the Specialized Luthier Neck Reset Removal Tool™ we need to work on the heel.

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.

Carefully sand the sides and bottom of the heel.

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.

After removing some material from the sides and bottom of the heel, you'll get a ridge on the center of the heel. Use a chisel to take it off.

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.

And since the outside edge of the heel is the only critical part for the neck set, we can undercut the dovetail a bit. This will help in fitting the dovetail later.

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.
Last test fit.

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.


Fingerboard and Top Seam Reglue on the Regal Tenor Guitar

Final couple of fixes on the Regal tenor before I do the neck reset.

The fingerboard on is separating from the neck near the nut.

Should be an easy fix.

The separation is so large that I can easily slip my removal spatula into the joint. I can slide it down to about the 3rd fret or so.

I need to be able to get glue into the whole joint.

Originally I figured I'd inject hot glue into the joint, but then it occurred to me that I could also spread glue onto the spatula and then slide that back into the joint and get glue down into the tighter end that way. Then I can inject glue into the wider opening.

Here we have the spatula covered with glue about to go into the open joint.

And I hit it from the other side as well.

Imagine how hard this would be if the neck wasn't clamped up in the amazing guitar vise. I'd be chasing it all over the workbench.

Then I injected hide glue into the larger opening nearest the nut. I injected almost all of the glue you see in the syringe.

Pressed the joint down, wiped off as much excess glue as I could, and then clamped it up.

Here we see the fingerboard clamped up...or actually down.

The caul under the neck is one I made a while back for just this sort of job. I have a box full of semi-custom cauls now, and it's great to just be able to find one that works without having to make another one.

Another angle of the clamped-down fingerboard.

Two cauls under the neck and one on top, with 2 bar clamps.

After the glue is dry, I have some squeeze-out to clean up. I'm actually glad to see some, because that means there was plenty of glue in the joint. I don't want this thing to come apart!

The last fix is to reglue the center seam on the top. From what I can see, the split isn't all the way through, but it is separating.

You can see the separation after I put the brace jack under the top and raised it a bit to open the seam to get glue into it. You could also use one hand to press open the joint or crack from inside - I've done that - but that's more awkward. With a jack, both hands are freed up to work on the repair.

This is pretty common on older acoustic guitars. It probably causes the owner a lot of consternation, but it's easily repairable. The top was originally made from 2 halves glued together in the middle, and in essence, we're just doing that again.

I had to work quickly before the hot glue began to gel (set), so I didn't get in-process pictures. But I'll describe what I did and you can use your imagination to visualize it.

With the seam opened, I spread hot glue with a brush into the seam. Then I lowered the jack inside the body, and moved it out of the way. The seam mostly closed at that point.

Then I wiped the excess glue off, and clamped the seam flat as you see here.

There's another caul inside the body. Using 2 clamps puts nice even pressure on the joint. I use waxed paper on this kind of repair so the caul doesn't stick to the guitar!

The finished repair. You can press down on it and it doesn't open up, and it looks good.

One thing you may notice on spruce tops like these is that the two bookmatched sides look like they're different shades of color - one appears darker than the other. In this picture, the left side looks darker.

That effect is because of the way the grain fibers run - one half of the top runs one direction parallel to the grain, and the other half runs the opposite direction. The way the light is reflected off each side makes one look darker than the other depending on the angle you view it from.

Now that those repairs are done, I can do the calculation for how much material to remove from the heel and get the actual reset started.


Fingerboard Crack and Separation Repair on the Regal Tenor Guitar

I have a couple of small things to attend to before I can begin the neck reset on the Regal.  Better to take care of them now rather than later.

First, I cleaned up the dovetail.  You may recall there were bits of shims on the male part.

A couple passes with a chisel takes care of it.

I recently sharpened all of my chisels and now they're ready to go.  I have read that it takes a while to get the hang of sharpening tools such as these.  I'm getting a lot better.

I've also read that the test for 'scary sharp' is being able to cut the hairs on your arm (if you have hairs on your arm).  Yes, the chisels passed that test!

The other part of the joint on the guitar is really ugly.  More chiseling/cleanup ensues.

It looks to me as if the dovetail was a bit rough, and Regal just depended on shims to make a tight joint.

I'll be interested to see if my May Bell guitar looks the same.

The dovetail after the cleanup.

Looks better I think.

I've already scouted The Dungeon for new shims.  I found a small hunk of maple that should work well when it's cut up into shim-shape.

So I spotted this crack on the edge of the fingerboard.  I don't know if this was already there or if it happened during the neck removal.  I suspect it was an old crack which got worse.

In any event, I need to glue it up.

Another repair is on the neck heel.

The green arrow points to a corner of the dovetail that's cracked.  I want to save that piece, so I'll inject some glue in the crack.

The blue arrow points to separation between the dovetail and the fingerboard.  You'll see this a fair amount when you take a neck off - usually the steam and use of the separation knife will open this joint up.  Just a side effect of using steam to get the neck off.

Not a big thing, and easy to fix.

I cooked up a fresh batch of hide glue.  This time I'm using some that is 196 gram strength - I had been using 164 previously (and still have some of that).   The 196 will set a bit faster.  And I really just wanted to try something new!

We inject the hot glue into the crack with a 0.7mm needle on the syringe.  I gently pushed the end of the fingerboard down to help open the crack.

You can see the glue squeezing out of the crack - this ensures the joint will have the proper amount of glue in it.  The excess wipes up easily with a hot, damp rag.  (I just dip it in the water I'm using to heat the glue jar in).

Quickly clamp it up with a caul and a small c-clamp.  Use a caul on the fingerboard side unless you want to put a round divot in the board.

You can see the repaired crack will be almost invisible.

That clamp, by the way is quite small - it's only about 1.5 inches (maybe 37mm) across.  The wide angle lens on the camera makes it look huge!  I bought the clamp at a yard sale for 10 cents.  I probably should dunk it in Naval Jelly to de-rust it, but it works fine as is.

Next up, I inject the seam between the dovetail and fingerboard the same way.  And I got that small piece I mentioned earlier glued as well.

I really like injecting the glue this way.  Lots of fun! 

You need to work quickly before the hide glue begins to gel.  It's heated to about 140 degrees F and will gel when it cools to about 90.

But I had time to take this quick shot of the joint before I clamped it up.  Notice the glue coming out of the joint - A Good Thing. 

Again, you can give it a quick wipe with a damp rag to get up the excess.  Any that's left after the glue dries will come up easily with a hot rag and a bit of scraping.

Isn't hide glue wonderful?

Another caul on the fingerboard and we clamp the joint down tight.

After these 2 repairs dry, I have a couple more to work on.