Scarfed headstock joint question

[Brian Evans]

With a traditional scarfed headstock joint you cut on an angle, flip one piece over and glue the two pieces together. One piece always is glued to side grain, and the other piece is always glued to end grain. Not perfect end grain like a 90 degree cut would give you, but end grain none the less. Why is this OK and what are the strength implications on the joint?

Thanks as always! Brian

[Bryan Bear]

One side is "endgrainish" but as you point out it is not 90 degree endgrain more like 15 degrees which makes a lot of difference. That joint is probably a lot stronger than the risk of breakage due to short grain with an unscarfed neck. I (almost) always have a front and back veneer that helps reinforce the joint and sometimes use long grain ears on the side of the peghead (depending on how I made the neck). With all that going on, I don't worry about the glue joint one bit.

[Beate Ritzert]

The headstock joint gets additional support from the fingerboard. It should be possible to make this thick and strong, shouldn't it?

BTW: it is also possible to make a 3 piece neck where the central section uses the inverse version of the scarfed headstock (central stripe longer, and headstock glued from below). So the headstock and the neck have an increased glueing surface with nearly parallel grain.

[Rodger Knox]

There's two ways to do a scarf joint. One has the joint on the neck shaft under fingerboard, the other has it in the middle of the headstock.
I like the first, but the second is easier to hide.

[Alan Carruth]

I've always made scarf joints with the neck shaft extending into the head, and the added piece on the bottom. With the large glue surface, the low angle, and a head veneer, it's actually pretty strong. I have seen badly done production ones where the scarf itself let go, but the head was still held on by the face veneer. I'm not saying those are easy to tune, mind you, but they do stay together...

At one point I worked on a lot of low-end import solid bodies with the other arrangement: the scarfed piece was glued on top, so there was a segment of the neck that had grain running parallel to the head surface. This meant that the fingerboard was glued to the semi-end-grain. There tended to be a hump in those necks around the area where the scarf ended. I didn't like them.

As Bryan says, a scarf joint with a back strap is just about bullet proof. When I do that I like to extent the strap up the neck for some distance, tapering it out to nothing around the 3d to 5th fret. This is a nice cosmetic effect. If you make the neck with a center stripe, and use the same material for the back strap it looks as though you meant it. I've seen a lot of old banjos done that way. It's especially effective with those V-profile necks. Make the back strap about 2-3mm thick, and bend it to match the headstock angle. Then fit it onto the back of the head and neck. I glue them with Titebond and a caul.

[Brian Evans]

Alan, with that method you are more scarf jointing the head stock than the neck, would you agree? The joint is not really in the neck shaft or even the angled transition portion, it is extending the "stub" of the headstock. How thick is a typical backstrap and headstock veneer? I normally use a piece about 1/8" thick for my top veneer. If I used a similar thickness for the back, there wouldn't be much headstock left!

Brian

[Alan Carruth]

Brian Evans wrote:
"Alan, with that method you are more scarf jointing the head stock than the neck, would you agree?"

Certainly. I suppose having the scarf up in the head incurs the problem of weak short grain above the nut, at least in theory. A lot depends on where the scarf is, of course: I've never had problems with it.

1/8" for the face or backstrap veneers is about right, although I'd make them thinner if I used both. You're right that there's not much head left when you do that, but the assembly is certainly strong.

With all of that said, on my own work I pretty much just use a traditional through V-joint; not the modified bridle joint Martin used. IMO this is the best way to put on a head. It takes some skill and a bit of time, to do, of course. My students mostly use either laminated necks or one-piece ones unless they take the plunge and do a V-joint.

[Bryan Bear]

Alan (and others) may correct my assumptions, but a few of my thoughts. . .

The scarf does end up being in just the peghead if you glue it in that fashion. The thicker the blank, the further out there it will end up once it is all shaped. I like to thin that part of the blank so the scarf is closer to the nut instead of way out in space. My reasoning is that the short grain area is smaller and in an area that is getting less leverage that it would halfway down the peghead. I also like to use a volute which makes part of the short grain area thicker. Also truss rod access through the soundhole.

IMHO, the veneers don't have to be super thick if you are doing the front and the back. My back veneers are nowhere near 1/8" and I still feel like it offers a lot of support to the vulnerable section of the peghead. Drywal is pretty brittle, but holds up surprisingly well with only a paper layer on each side. Score one side of the paper and you can snap it easily. . . I could be wrong, but that is how I see the back veneer. Without it, a sharp hit from the front of the peghead could split the short grain easily just like scoring the back of a sheet of wallboard and hitting it from the front to break it. With even a thin long grain veneer, you get a whole lot of extra support.

[Dan Smith]

I Always put the joint in the head and apply a top veneer and sometimes a backstrap veneer.
I don't like seeing the joint in the neck shaft.
If I'm using figured wood, I don't flip the head and glue, I recut the angle so the same face of the wood is on the same side of the neck. This can help hide the joint line on the back.

[Dan Smith]

Alan (and others) may correct my assumptions, but a few of my thoughts. . .

The scarf does end up being in just the peghead if you glue it in that fashion. The thicker the blank, the further out there it will end up once it is all shaped. I like to thin that part of the blank so the scarf is closer to the nut instead of way out in space. My reasoning is that the short grain area is smaller and in an area that is getting less leverage that it would halfway down the peghead. I also like to use a volute which makes part of the short grain area thicker. Also truss rod access through the soundhole.

IMHO, the veneers don't have to be super thick if you are doing the front and the back. My back veneers are nowhere near 1/8" and I still feel like it offers a lot of support to the vulnerable section of the peghead. Drywal is pretty brittle, but holds up surprisingly well with only a paper layer on each side. Score one side of the paper and you can snap it easily. . . I could be wrong, but that is how I see the back veneer. Without it, a sharp hit from the front of the peghead could split the short grain easily just like scoring the back of a sheet of wallboard and hitting it from the front to break it. With even a thin long grain veneer, you get a whole lot of extra support.

Bryan, thanks for the tip! Took me a while to understand that thinning the head from the top side will put the joint on the backside near the nut. I made a neck this weekend, and the joint line on the back of the head is near the nut rather than the center of the head. I won't need s backstrap to hide the joint line. Thanks!
Dan

[Bryan Bear]

Dan, I'm glad it worked out. I hope you planned accordingly and you didn't end up
With your nut too close to the heel.

[Clay Schaeffer]

"With all of that said, on my own work I pretty much just use a traditional through V-joint; not the modified bridle joint Martin used. IMO this is the best way to put on a head. It takes some skill and a bit of time, to do, of course. My students mostly use either laminated necks or one-piece ones unless they take the plunge and do a V-joint."
Alan Carruth

I like the modified bridle joint. In some sense it can be viewed as a hidden scarf joint with an integral back strap (the volute). With the peghead veneer I would think it has more gluing surface than almost any other construction method.
Some of the old romantic guitars and also Hauser's guitars used a V joint that does not come through the face of the peghead. It can look pretty cool. I may try one some time.

[Christ Kacoyannakis]

In the Benedetto book, he uses flat sawn wood and turns it into quarter sawn by cutting out 3 sections of the neck, headstock, heel section and gluing them together. Of course this results in endish grain on the top of the headstock and grain lines that run across the headstock angle, but he does use front and back veneers. Do you guys think this is not as solid and stable as using the scarf joint. If you use a scarf join, do you then glue on heal block laminations? Either way you end up with glue lines somewhere on the neck. Just wondering, not saying one is better than the other.

[Barry Daniels]

I went though about 40 necks made with Benedetto's approach to lamination and grain orientation. They make for a very strong and stable neck. We did front and back veneers, but the back would look fine even without it. To cover up curly maple seems a bit odd in retrospect.

[Beate Ritzert]

Barry's and Chris' remarks motivated to check how the necks of my guitars are built. The majority of them does not have a neck joint:

Three necks are made of laminated birch with a laminate thickness of about 2.5 mm - that's the multi layer variant of Benedetto's appoach.

One (made by an experienced luthier) is 3 piece like Benedetto's proposal. 3 other (all my archops) are the 2 piece variant with a narrow stripe in the middle. This approach would allow to cut the truss rod channel with a saw and avoid a posteriori routing of the channel. (And the theoretically ideal parabolic shape of the channel can be done easily...)

A few others including a neck through bass use a scarf joint where the headstock is glued on top of the neck - my main motivation of doing this was to compensate for the lengh; i could not obtain wood of suffient length.
Two other bass necks have the headstock glued from below and convered by some thin veneer.

all approches work equally well. I found the necks without a scarf easier to make. Especially if the headstock angle is small the amounf of necessary length increase is the headstock is pretty small. So i do not see the real use of scarfed neck joints except in some special cases like ultra-long necks of e.g. neck through designs or open head stocks like this one:

[Alan Carruth]

The modified bridle joint is fairly easy to make on the table saw, and that's one reason Martin used it, I'm sure. With good jigs you can make all the cuts accurately enough on the saw and fitting process just involves thinning the headstock until it slides home. The through V-joint is actually a bit harder to make and fit.

The main advantage of the through joint IMO may seem like a drawback to some: it breaks easily and cleanly along the glue line when shocked. When the guitar falls off the stand and hits the head all that happens is that the glue line breaks, assuming you used hide glue. It's an easy fix; clean off the old glue and re-glue it. When the bridle joint breaks it breaks wood, as does the Taylor finger joint. Scarf joints can let go by peeling up, in which case often enough the face veneer will hold things together until you can get it to the shop (it's hard to tune, though....). I fixed enough broken heads back in the day that I really appreciate something that holds fine in normal use, but is easy to repair when somebody gets stupid.

[Beate Ritzert]

Alan and all the other pros: may i ask what joint you would have used for the headstock i showed above?

I actually did a scarf joint with the headstock rising above the neck (and in the past i have had trouble arising from creeping PVA glue which seems to be gone after the repair, it is stable for meanwhile several years). That bass tunes really well, and it also stays in tune very well.

[Alan Carruth]

That open bass head would not have been a good candidate for a V-joint; there's not enough distance between the nut and the 'slot'. Other than a one-piece or a vertical laminate, which is essentially the same thing out of built-up wood, I'd have gone for a scarf joint if I was stuck with a neck piece that was too short, and used both a face veneer and a back strap. I'd have been very tempted to use the back strap to close the box in back in any event; that goes a long way to stabilize the cheeks. I made open backed heads on my 5-string violas for a while, but that makes the walls of the pegbox more flexible and contributed to difficulties in tuning. Also, I worried about the strength.

[Greg McKnight]

There's two ways to do a scarf joint. One has the joint on the neck shaft under fingerboard, the other has it in the middle of the headstock.
I like the first, but the second is easier to hide.

[Alan Carruth]

I learned the method you call #2, and from what I've seen that has been the standard until fairly recently. The first time I saw it done the other way was on some slick, but cheap, imported solid bodies. I used to do repairs for a local store that brought them in, ad they were fertile ground for corrective work. One problem they had was the tendency to develop a bump in the fingerboard above the joint. Admittedly, that layout should enhance the strength of the headstock, since the grain will be running along it, but it does seem to reduce the stiffness and stability of the neck.