Dovetail vs bolt on

[tahoeguitar]

I use bolt on necks with a shallow mortise. I think the bolts are plenty to hold the neck on, but I worry that a sharp lateral blow to the neck heel might cause the bolts to split the neck block. The mortise and tenon adds sheer strength, and ensures accurate centering of the neck at assembly time.

Here's a link to one of my build threads the neck construction begins near the end of page 3.

[Alan Carruth]

This is a place where careful design and work make a big difference. Any time you put hardware into wood it's a stress riser, and that brings up the possibility of failure if you're not careful.

Over tightening a bolt on can be a real issue, with the details of the design being important. A few years ago one of my students made a bolt-on using cross dowel nuts in a M&T heel. We had drilled the holes across the heel, parallel to the plane of the fingerboard. He put the neck on, and when he lifted it up off the bench he hit a low beam in the ceiling. It was not a very hard blow. The heel broke across through the upper dowel hole, and the body fell on the floor. If the cross dowel is even slightly loose in the hole it puts a lot of splitting stress on the joint when it's tightened because all of the load is on a line, instead of being distributed across the width of the dowel as it should be. These days we drill the holes perpendicular to the fret board plane, so that, if the bolts are over tightened the heel will split vertically. The two halves of the neck are captured in the mortise, so it can't go any place. This is known as designing so the it 'fails well'.

I read years ago in a homebuilt aircraft publication that any time a bolt is used in a wooden aircraft structure it must be a force fit to ensure good contact all around. On a guitar you should get away with flooding it with CA.

I have an old but joined Taylor neck that split through the heel at the threaded insert. I can't say, of course, what it took to do that, or whether the bolt had been over tightened. Unless the hole was tapped for the insert (and who does that?) it would have put a fair amount of pressure on the wood when it was put in, though, and that probably didn't help.

There's nothing inherently wrong with a bolt-on, and it has real advantages. However, you do need to pay attention to the details, as always on guitars.

[Quickstep192]

I read an article once where a guy used a mortising bit in a drill press to drill a square hole from the top of the neck into the heel perpendicular to the plane of the fingerboard. Then a square steel rod with threaded holes was inserted into the square hole and captured between the fingerboard and the heel cap. This seems like it would help alleviate the point load caused by using a round rod.

[Bruce Sexauer]

Dovetail construction is not getting a lot of love in this thread, it seems, but do not imagine that it does not have it enthusiasts. We live in a hardware world where most people are more familiar with a screw driver than a chisel, but for those of us with actual edge tool skills, a dovetail is not particularly challenging to fit. There is a elegant beauty and efficiency in the dovetail connection which I do not find in the bolt on, and which for me is an essential part of why I truly love my work. One may work as well as the other, but that does not make them equal.

[charles Tauber]

Originally Posted by Bruce Sexauer

Dovetail construction is not getting a lot of love in this thread, it seems, but do not imagine that it does not have it enthusiasts.

I continue to use a dovetail and like it. I use a dovetail with no glue, though the fingerboard extension is glued to the top. The dovetail is preventing from sliding apart by a single wood screw through the neck block, from inside the guitar, into the male part of the joint on the end of the neck. I've done it that way for 30 years.

In a recent visit to Grit Laskin's shop, I was surprised to find that he still does it that way. It was from him that I learned to do it that way.

[Alan Carruth]

With over forty years as a solo luthier, I don't consider myself to be bereft of hand tool skills. I've gone over to using bolt on necks for the simple reason that it's a lot easier to do the reset.

If you're using a screw to hold the neck on, why do you need to fit a dovetail?

[murrmac123]

Originally Posted by Alan Carruth

If you're using a screw to hold the neck on, why do you need to fit a dovetail?

The screw isn't holding the neck on, the dovetail is holding the neck on.

Think of the screw as being a continuous threaded metal dowel , and the hole in the neck block and the heel as being a continuous pilot hole, same diameter all the way, so the screw just serves to prevent any rising of the tenon in the mortise... exactly what the glue does when the joint is glued. The screw is not fulfilling the same function as a bolt in a bolt-on neck.

Grit Laskin told me all about this joint when he was over here last year.

[charles Tauber]

Originally Posted by Alan Carruth

I've gone over to using bolt on necks for the simple reason that it's a lot easier to do the reset.

If you're using a screw to hold the neck on, why do you need to fit a dovetail?

The purpose of not gluing the dovetail is to make it easier to do neck resets.

The sole purpose of the screw is to act as a retractable pin. The pin prevents the two haves of the joint from moving laterally, preventing them from separating. A tight-fitting mechanical joint is what holds the neck on. The pin is what keeps the joint from separating when you don't want it to.

It isn't "better" than a bolt-on neck, just a different approach, one that pre-dates the modern bolt-on joint. Would I recommend that someone new to building learn to make and use that joint? Probably not. But it is a joint I know well and have used successfully for a long time. I think the best joint is one that allows the neck angle to be adjusted without having to take the neck off: that is what I'd recommend to just-starting builders.

[MC5C]

I do a mortise and tenon with two bolts. The tenon is a tight fit in the mortise, so no lack of fitting skills, and the bolts let me take it apart easily. I do a quite shallow heel, about a half inch.

[Halcyon/Tinker]

A bolt on neck system should not be considered as a workaround for an absence of skill.

It is a pragmatic design decision to counter some of the drawbacks of a dovetail joint.

[tahoeguitar]

Tinker's got a point... the bolt on just requires a different set of skills and is as hard to do well as a tapered dovetail. I sometimes wonder if the joint I use isn't actually a little more work than a dovetail.

The bolt on is easier to remove for a reset with virtually no risk of finish damage, and that is its main advantage IMO. Steaming off a dovetail almost always leads to at least a small amount of finish touch-up where the steam leaks onto the body of the guitar.

[murrmac123]

Originally Posted by tahoeguitar

Steaming off a dovetail almost always leads to at least a small amount of finish touch-up where the steam leaks onto the body of the guitar.

I don't doubt that you are right.

I haven't reset a dovetail joint guitar yet, (although I have reset a couple of bolt-ons successfully) but when the time comes (and it will) that I reset my first Martin, I am going to make darn sure that when I steam the dovetail joint, the guitar will be supported in a fixture which will hold it upside down (at an angle of 45 degrees) , so that gravity ensures that the steam and water drops back down through the second drilled hole in the 15th fret slot, and doesn't dribble on to the finish, which is what happens when the guitar is lying on its back.

Steaming the joint with the guitar lying on its back, which seems to be the universal modus operandi as far as I can gather from the videos, forum posts and blogs that I have seen and read, appears to me to run totally counter to common sense.

[redir]

Originally Posted by murrmac123

I don't doubt that you are right.

I haven't reset a dovetail joint guitar yet, (although I have reset a couple of bolt-ons successfully) but when the time comes (and it will) that I reset my first Martin, I am going to make darn sure that when I steam the dovetail joint, the guitar will be supported in a fixture which will hold it upside down (at an angle of 45 degrees) , so that gravity ensures that the steam and water drops back down through the second drilled hole in the 15th fret slot, and doesn't dribble on to the finish, which is what happens when the guitar is lying on its back.

Steaming the joint with the guitar lying on its back, which seems to be the universal modus operandi as far as I can gather from the videos, forum posts and blogs that I have seen and read, appears to me to run totally counter to common sense.

That would probably help a lot. Is that something you have seen before or just imagining? It's a good idea.

But none the less, steam is hot and forced into the joint so it will have it's way. I have done some neck joints that were a piece of cake but I just did an old Guild which are notorious for toughness and am now faced with finishing chores. Not sure such a jig would have helped in this case but again, it sounds like a pretty good idea.

[murrmac123]

Originally Posted by redir

That would probably help a lot. Is that something you have seen before or just imagining? It's a good idea.

But none the less, steam is hot and forced into the joint so it will have it's way. I have done some neck joints that were a piece of cake but I just did an old Guild which are notorious for toughness and am now faced with finishing chores. Not sure such a jig would have helped in this case but again, it sounds like a pretty good idea.

I've never seen or heard of such a fixture, but I have a design in my mind's eye as to how it would be constructed.

[John Arnold]

I have done well over 1000 resets, and steam damage to the finish is very rare on a Martin style dovetail. Lacquer will turn white with steam exposure, but no touchup is normally required. Wiping it with denatured alcohol will remove the white by drawing the moisture out of the finish.
I drill two holes through the fret slot. The larger hole is for the steam needle, and the smaller hole is for release of the steam. Normally, it takes less than 5 minutes to remove a dovetail neck that is glued with hot hide glue or Titebond. White glue is even easier.