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Last time I posted about this old nylon italian guitar (Monarch label), I had just strung it up and the next morn the neck pulled out of the dovetail a bit, mostly at the bottom of the heel. Put it aside til just recently. Took neck off, 15 degree sanded the walls in the headblock for fresh wood and started working with shims, starting from the bottom third, the top still seemed to fit fairly tightly with reasonable clearance and centering. When I got it back to a reasonable set-up dimension I added shims in the middle to get continuous 'mating' walls, also sanded to 15 degrees. Slow work, not sure how many little shims I aded and sanded partially thru, but finally got it to fit tightly (I think) along the side walls. So I strung it up and it's held fine for a few days, just the dovetail fit, no glue at all. It plays and sounds really nice, Im surprised with all the torture Ive done to it, but the attachment is not quite good enough, action too high up the neck, and treble E string is too close to edge of fretboard. So not really knowing how this should have been done, I have a few questions....
1. Can I just glue a veneer shim to both sides and restudy John Hall's dovetail fitting youtube? ie, if I have quite a few Titebond
joint/shim layers underneath the new shim, will they hold? I didn't have chalk when I was working, the substitutes I tried were
only fair. I'm hoping to get better look at the contact areas with a single shim surface and some better chalk.
3. I did a pretty poor job pulling the fret and drilling a steam hole. Where might I find good info on how to repair that without it
looking like a hackjob?
3. I had tried flossing the sides of the heel, but it was defacing the original body finish, so I stopped trying to make it fit the body
perfectly. Is there a better technique y'all probably know? I was just using sandpaper strips, probably 220.
Thanks in advance for any inputs. Roy

The answer your questions.
1. Shims are required for fitting a dovetail to a new neck angle. I personally use maple veneer as my shim material since it's easier to see the contact points with carbon paper on a lighter wood. Chalk works great too. Don't attach your shims before you fit the neck to the body as it'll make it harder to do a good fit since you can't slip the neck in/out easily.

However you mentioned that your high E is too close to the edge of the fretboard. That means your neck is out of alignment and that needs to be corrected before you set the new neck angle. The high E being too close means you need to remove material from the low E cheek side of the neck. Once the alignment is fixed you can then set the new neck angle.

2. Use superglue for this. The smaller the hole you can get away with the better. If it's too big you can use some wood filler and pencil/draw in the grain lines and color you need to blend it.

3. Get low tack tape and attach it to the sides right up the cheek line of the neck. To make it easier and not rip sandpaper get some 1" wide sanding belts and cut them into 8" pieces. Use these strips to floss the heel and get a perfect fit. I use the Klingspor stuff, you want to use sanding belts because they won't rip when you pull them through and the tape lets you do it without fear of nicking up the finish. I use 220 to get the angle set and then 320 to get a flush fit.

1). Yes or make your own shims we use mahogany and super glue them in place. An uber sharp chisel is your friend and the chisel is what is used to do the fitting of the dovetail not sand paper. The shims are not going to come loose in so much as they are functioning as a gap filler not a glue joint that is in sheer as one might think. So long as the dovetail fits firmly and needs a slight "tonk" to set it all the way down AND as long as the bottom of the joint, where the heavy lifting is done in countering the neck's desire to fold into the body is tight you are good to go. Anything from John Hall is top shelf and highly recommended by me. He the man! . He also helped me learn this stuff too. Our friend Dan who posted above knows his **** too and I would not hesitate to take his advice.

3) (2) Repair the fretboard with matching wood, rosewood or ebony, match the grain, color and piece it in and then recut the fret slot(s) if necessary. It may show but do your best to color and grain match.

3) We tape off the guitar body all around the dovetail joint with quality 3M masking tape (don't overlap the tape so that it is constant thickness). Do it full height so that the flossed fit that you achieve remains snug when the tape it removed. To give you a visual the backing of the sandpaper will only contact the masking tape on the body and never the finish.

Make sense?

Also now you are into the realm of doing a neck reset. This is difficult and involved and setting the angle requires very high precision and anything less will result in issues of an over or underset neck. Take your time and generally speaking with the neck flattened out with the truss rod and a quality straight edge on the fret board you want the neck angle to be such that the straight edge just kisses the top of the bridge being over the top of the bridge by the fret height. There is further refinement too but that can depend on a host of other factors.

Neck resets are difficult, time consuming, rarely profitable and prohibitive on anything other than guitar with some real value or personal value to someone who wants to pay for it.

And lastly a dovetail joint is a beautiful thing and so perfectly well suited for this application. Good luck.

One more thing. It's entirely possible to reset a neck with zero finish damage and we do it all the time. Finish touch-up around a reset neck joint is not uncommon though and likely because more people are not taping off the body first.

Appreciate the inputs, they will definitely help. I probably should mention that since it's nylon and didn't have one originally, (the original neck was twisted quite badly) I did not add a truss rod, just filled the slot with mahog. I expect that was a mistake, but hopefully not such a big one. Being cheap, I thought buying a few junkers and using their repairs to learn something about what I'm doing would be a good way to see if I like this 'hobby'. Turns out I'm enjoying building new too much to want to do repairs, but there's always one still around that needs a redo to chase away the feelings of being a hack. I'll keep at it with my usual speed; glacial. Nice to know I can ask que here when I get stuck. Thanks again, Roy

Hesh, I'm curious. Do you use super glue for the shim attachment because titebond can cause problems with 'blushing' when finishing with lacquer? I'd typically prefer titebond just because it can be slightly repositioned while still wet, OTOH my first guitar has major blush around the end wedge where I know I used titebond. Thanks Roy

To glue on a shim only we use CA for expediency only so we can glue and back back to chalking the joint, trial fitting, and carving and then repeat until the fit and angle(s) are correct.

Update.....After rewatching John Hall's videos about how simple a dovetail joint really is, I started out with two new hickory shims, plenty of chalk thinking I could just ease my way into a decent fit using my chisel to gently remove the chalked portionsof the tenon after each fitup, and then sanding for a smooth mating surface on the tenon. A week later, I had removed the new shims completely, thought I had it close enough to string up and see whether I might could think about glueing. It's worse now than before I started; treble string almost comes off the fretboard, seems the string tension moved it from where I thought it was unstrung, and the foot of the neck is not held snug against the body at all. Made all the measurements I thought might be helpful, and took it off for inspection. I had started out using 15 degree angle sanding blocks. Looking closer at the mortise angle (I can never remember which is which), but I'm talking about the inside of the neck block, it turned out that 10 degree fits the angle better, so I made new sanding blocks halfway thru the process. I also noticed the shims I had added along the way had offset the entire tenon to the base side, which is obviously not right.
So now I'm starting over after removing all the shims on both sides, and cutting two shims that both only go about a third of the way up from the bottom of the tenon mating surfaces. I'm thinking if I start trying to fit only the bottom and get it tight, I can add and shape my way up the interface, hopefully keeping the tight fit while checking neck angle and centering as I lower. I don't mind doing things over if I am learning from the effort, but right now I'm stabbing in the dark a bit. But I'm still working on it. Slowly. Thanks for any advice. Roy

After spending ridiculous amount of time (again) with various shims, I had a tight fit, correct centralizatiion, and neck angle. Strung it back up again with no glue, and the bottom toward the neck cap pulled out just enough to mess up the action in the upper fret region. So it wasn't as tight as I thought, at least down toward the bottom of the heel. I've been letting it sit for a few days while I wait for inspiration re how to put in the correct shim at the bottom that fits well enough to keep the neck angle solid when strung. The best idea I've had is to use some sort of play dough type material to show where the gap(s) still are.(?) I can't seem to tell with chalk. Surely some of you have better ideas.....Put in an insert toward the bottom and make it a half bolt on dovetail, glue it up and move on? Took me awhile to post due to frustration. A few days away from it seems to have helped my state of mind. Thanks for any suggestions. Roy

Instead of gluing on large shims, you could take some standard wood veneer (0.032" thick) and make tiny squares about 3/16" square. Put them in the place on the bottom of the dovetail with a small drop of glue. Then see if the neck will insert fully and stay tight against the body. If that works then you can remove the test pieces and replace them with a full piece of veneer and taper it down to nothing at the top. If the small pieces of veneer are too thick you can quickly sand them down to the correct thickness for a good fit.

I'll give that approach a try, been trying to decide where along the dovetail face I should expect the gap to be since it's puling out from the body only under string tension. (I've been using partial length shims for some time now.) Thanks for the suggestion. Roy

The very bottom of the dovetail is where you need to concentrate your attention to because that is where all the string pressure is concentrated. Any gaps there is what results in the heel coming away from the body.

Yes, I've been working on the bottom 1/3 of the mating surface...your idea worked better than anything I've been able to do before, but it still pulls away a bit, mebbe 1/16" It's playable now, but I should be able to do better. I think the dovetail should pull the bottom of the neck down tight and hold it there against the string tension. Since it still isn't doing that perfectly, I've been thinking the most inward edge of the male (neck dovetail) might need to be built up a tad. But I'm really guessing as to where the gap is worse. I have been very reluctant to do any sanding on the female dovetail edges of the neck block, but my chalk wants me to think I see a little recessed area there I could try to build up and then sand flat... I really do appreciate your inputs. It's always hard to teach a newby remotely. Roy

Frustration abounds....After re-shimming and going thru the chalk, chisel and sanding processes, I'm right back where i started, (the bottom at the neck cap won't stay locked in, and the treble E string is too close to the fretboard edge. Only other thing is the fact that I can't post pictures right now (I get upset everytime Smugmug makes 'improvements'). But I did notice (finally) that the female neck block part of the dovetail has almost no V shape. It looks totally vertical on both sides. Measurements show a very slight taper, but nothing like a 'V'. I'm inclined to slant the female sides into more of a V shape and start all over with more shim that's heavily top weighted on the male neck tenon (if that's the right term). As long as I'm going to that much trouble, I think I'll change the sanding blocks to 15 degrees instead of 10 which I thought matched the current edge taper in the neck block. Seems like it would give me more bite. Wonder how much of a V shape I should be trying for? Guerss I could start shimming the inside bottom of the female neck block if I can't get enough of a V by widening the top. If anyone has better ideas, I'm all ears. Roy

How about this: cut the dovetail into a tenon, fill and cut the mortise to conform, and install a couple of bolts. Anathema to dovetail worshipers, but I'd rather have a working M&T neck attachment than a lousy dovetail.

_________________
Peter Havriluk

Yes,, I could certainly do that, which is how I've done all three new builds I've done, but I'm working on this old guitar solely to learn something about dovetails while isolating from covid. And I'm stubborn. I'm not giving up on this as long as I have ideas that seem reasonable. What with the new top and the new neck, I'm already way past doing much more than it's worth. And I have learned a good bit. But thanks for the suggestion. Normally it would be great advice, and if I run out of ideas, I'll do that. Roy

So the dovetail is not tapered but parallel? That may be the source of your problems. A dovetail like that are not really made to be reset. And I think that trying to convert it into a tapered dovetail is not a good idea either. You will have to create new angled surfaces on both sides of the mortise and tenon. It would be difficult to do that freehand.

Thanks, Barry. I was thinking the lack of a V shape might be the problem. So I decided to try making it a V of sorts anyway. Half shims in the bottom of the neck block and the top of the neck itself. Then open up the top of the neckblock so I have a straight edge line that makes a noticeable, though not large V. I used 0.150 shims and sanded/chiseled so the top of the neckblock shim was flush with the side and the bottom of the shim was still about 0.15, and did the opposite on the neck itself. Chalk shows good contact all the way down the neck 'V' sides, but as I started sanding to lower the neck, I still can't get the treble side of the fretboard to move further in the treble direction as I lower the neck. I'm sanding mostly on the bass side of the neck tenon, and it seems like it's going the wrong way. Is that wrong? I also changed to 15 degree sanding blocks. Not sure what I'll try next, mebbe let this sit for awhile. It's getting frustrating. And I've got two new builds that I should really be working on, one at wet sand and polish and one at binding.
An aside, my son has my late Mother-in-law's 1930's mahogany Martin and says it's in miserable shape. Haven't seen it in 20 or so years, and not at all sure I'd feel competent to work on it, but that's partly what drove me to wanting to try working on a dovetail, plus this old guitar actually sounds pretty nice when I have had it strung. Roy

To move the neck sideways you have to remove a little meat off the backside of the heel, not the dovetail. Remove it from the opposite side of the neck that you want it to move in the direction of. So it sounds like you should take it off the bass side. Do that first because it will affect the fit of the dovetail.

Thanks, I kept getting confused, thinking I should work mostly on the dovetail (tenon) on the neck. Roy

I think (and the word is think) that an untapered dovetail is what a cabinetmaker uses while fabricating drawers. These are one-and-done unadjustable joints. All the dovetail advice here was in reference to a luthier's tapered dovetail, which I think doesn't have much relevance a cabinetmaker's dovetail. OP has a nonstandard joint which won't respond to luthiers' adjustment techniques. I think.

_________________
Peter Havriluk

I made an arch top using Benedetto's book and he uses an untapered dovetail. It is very strong, but I think that it is not made to be taken apart and reset.

Roy, have you seen John's video on youtube explaining the process and where to remove material to get things aligned?

I got it! (finally). Thanks for all of your patience and advice. Yes, I've watched Johns videos on fitting a dovetail a few times. I think one thing that threw me was him saying never touch the neck block, do all your work on the tenon. And I kept getting confused which side of the tenon to sand to get the neck to move which way. Telling me to work on the heel side of the neck block to get the alignment under control helped keep me straight as I lowered things. Then I just had to chisel and sand equally to bring it down. Of course, John's working with matched angles, and I was just trying to fit a neck I bought as a rough out from ebay to a 60 year old body that had a lot of issues. I still have some problems, but at least the alignment is right....need to take the fretboard off and install a truss rod, I didn't think I'd need one on a nylon guitar, but it's showing signs of twisting. And I have a spot I'm gonna have to fill where my rough sanding knocked out a little hunk of mahogony. And flossing. It'll be some time, but it feels so much better to get past this one thing that I didn't understand. Roy

And as a last comment, I can't imagine working on repairs completely. Too hard on the state of mind when things don't go well.

Glad it worked out.