Simple bolt-in neck joint for solid-body electrics?

[breezy]

Hello all,

I've been reading the adjustable neck joint thread with great interest although this is only tangentially related - I'm trying to figure out a bolt-in neck joint for solid-bodies where the curvature of the body at the neck joint makes a mortise and tenon too difficult. So far I've mocked this up in Illustrator





with the neck pocket routed at a 1.5 degree angle, but I'm concerned that because I've arrange the bolts side-by-side (body is only 38 mm thick so not deep enough to accommodate bolts over-under) I might be able to push or pivot the neck towards the face of the guitar. I'm also not too sure what will occur when I tighten the bolts - will the angle of the back wall of the neck pocket force the neck into the floor or push it upwards? Any help is appreciated.

[Nick]

Hey Breezy firstly welcome to the forum (brief intro possible?),great to see you thinking outside the box on this one . One slight problem I see with your design is there's nothing,apart from the rear vertical face of the pocket, to stop the string pull from pulling the neck up & out of the pocket. To put it in aviation terms, your bolts are on the same horizontal plane so there's less "up & down" (pitch) strength to the joint but the neck certainly wouldn't move sideways (Yaw). To provide mechanical strength the bolts need to be on a vertical plane but solid bodies don't provide enough depth for a suitable vertical pitch which is why, for many moons they've either screwed in from the back (ala Fender) or glued in the tenon.
But keep thinking though, maybe even some sort of brass dovetail block near the front of the pocket with the male part screwed to the pocket & the female inlet into the bottom face of the neck. You then would 'slide' the neck into the pocket & then secure it with one of those bolts you show.It would certainly be an 'invisible' joint from the outside once the pickups in.

[jeffhigh]

Not a good design, I agree with Nick.
Those bolts will just act in bending and try to pull off the section of body they are attached to
In this case, I would just extend the neck shaft to the pickup cavity (the full length of the fretboard) and you can then use screws with ferules from the back of the body without a rectangular plate.

[Matt Bach]

Aside from the aforementioned issues with string tension pulling it up and snapping bits off, and possible weirdness when tightening relating to the scale length (not by much but could be enough to annoy), I think having an adjustment point hidden in the pickup cavity will be pretty annoying down the track. Let's say the bolting arrangement did actually work fine, every time you want to adjust the neck angle you'd have to take off the strings and remove the neck pickup which wouldn't be much fun. If the name of the game is to never adjust the neck angle, just glue the sucker in if you can't make bolts work in the traditional way.

[Trevor Gore]

Hi Breezy,

I'd be a bit more optimistic than some of the other respondents.

What you're showing bears a number of similarities to the well tried and successful Gilet neck joint (acoustic guitar, bolted tenon, two bolts one above the other) doubled up sideways. It's illuminating to investigate the key differences.

First, the position of the bolts. The Gilet neck joint is still stable with the bottom bolt loose, even without the fretboard glued down. Clearly though, it helps to get the bolts as low as you can.

The bolt block in the Gilet design is a square bar of brass, not round barrel bolts. When you torque up barrel bolts they can act as a blunt wedge and split the neck wood; not so with a square bar. A square bar could be inserted from the side, just one long bar, but you need a mortiser to drill the square hole. Don't worry about needing a "roller" for angle alignment. Over the range of adjustment you'll need, the angle change for the bolts is too small to worry about (same as in the Gilet design).

The furniture barrel bolts you show are made of a fairly soft steel, with a small hex socket in a fairly large diameter head, and the socket tends to round off when you apply torque. So use socket head cap screws and a "washer plate" to spread the load and you avoid that risk and can get the bolts lower.

To answer your specific question, as drawn, the bolts will pull the neck down into the socket, more so the steeper the rake of the back of the mortise.

However, the real problem with your design as drawn is that you won't be able to get the bolts in.

With a few changes, I think you could make a mock-up, load it up and see how it performs. I think it could probably be made to work as a neck joint per se if you maximise the distance between the line of the bolts and the "pivot point" at the top of back of the mortise (no need to cut it down, there) and fill the gap between the underside of the neck extension and the top of the body to provide some moment constraint. The main question would be whether or not it was robust enough not to move around in a knock-about road environment. As the others have said, there's probably easier ways to get an adjustable joint. Wedges under Fender joints (and adjustable bridges, for that matter) have worked very well for decades.

[Nick]

the well tried and successful Gilet neck joint (acoustic guitar, bolted tenon, two bolts one above the other) doubled up sideways.

There in lies the rub I think Trevor, Breezy's drawing shows the bolts on an identical horizontal plane, no vertical seperation between them. After years of spending ages building things & bolting them together I value the integrity of vertical spacing as well as horizontal on a joint, saves me having to build another after a failure .
Also with grain orientation of a solid body the grain will be running along the same axis as the bolt's so not only will the neck try to pull up and pivot on the bolt's central axis but the bolts will be trying to split a bolts width worth of wood out from above them.
I can't see a problem at the neck end of things, it's at the body anchor I think the problems will occur with this design.

[jeffhigh]

I'd be a lot less optomistic about it than Trevor..
It's also not adjustable for angle because those bolts will just pull the neck into the angle at the end, whereas a standard bolt on neck is easily shimmed.
I think the OP was just trying to get around a rectangular bolt plate not fitting?

[breezy]

Hey everybody,

Thanks for all your replies, it's been really helpful. Yes, sorry I wasn't clear, it's not really meant to be adjustable (possible with wedges I guess), just trying to get around the bolts-through-the-body look.

One slight problem I see with your design is there's nothing,apart from the rear vertical face of the pocket, to stop the string pull from pulling the neck up & out of the pocket.

Right. That is my number one concern with the bolts side-by-side. I'm not too sure what hardware is available, but I might be able to fit one large bolt at the bottom and one with a much smaller head above it to prevent pulling, in conjunction with a washer plate.

But keep thinking though, maybe even some sort of brass dovetail block near the front of the pocket with the male part screwed to the pocket & the female inlet into the bottom face of the neck. You then would 'slide' the neck into the pocket & then secure it with one of those bolts you show.It would certainly be an 'invisible' joint from the outside once the pickups in.

That sounds interesting. How would the dovetail screw in, though? There's not much wood under the bottom of the neck pocket.

Clearly though, it helps to get the bolts as low as you can.

The furniture barrel bolts you show are made of a fairly soft steel, with a small hex socket in a fairly large diameter head, and the socket tends to round off when you apply torque. So use socket head cap screws and a "washer plate" to spread the load and you avoid that risk and can get the bolts lower.

Well that makes sense

However, the real problem with your design as drawn is that you won't be able to get the bolts in.

I didn't draw it correctly - I'm gluing on a 1/4" top so I can rout the cavity under it large as I need to, in order to insert the bolts.

[jeffhigh]

It's a good layout for a glued in neck, full width just like a Les paul junior.
Plenty of gluing surface if you run it back to the pickup cavity
I can't see a big advantage in a bolt on for electric unless you are using standardised mass production necks or have a bridge with very limited adjustability and get the neck angle wrong.

[Trevor Gore]

I'd be a lot less optomistic about it than Trevor..

I'd be a bit more optimistic than some of the other respondents.

...which, I guess, makes me a bit more optimistic than Jeff

I think the value in these discussions comes from understanding why some of these ideas may or may not work and particularly for the non-engineers, a lot of that understanding comes from building and testing with inexpensive mock-ups so that the reality can be directly experienced. I'd hate to discourage anyone from doing that.

For example, we could consider a simplified analysis of the proposed neck joint as shown below.

Basically, this sketch represents two bits of wood, end joined with an idealised furniture connector and subject to bending. What are the failure criteria and the failure mechanism(s)? Assume in the first instance that the connector rod and its anchors remain sound, then include them in possible failure modes.

BTW, I'm waiting for some paint to dry...

[Nick]

Your drawing would present sound engineering Trevor (as it should! ) with the fixing at the closest (& safest for mechanical integrity) position as is possible to get it near the bottom, in this case the furthest most position from the applied force so you have the whole face acting as a stop if you like & the fixing holding the faces together in close proximity. I'm a hammer & spanner engineer so I leave all the stress analysis stuff up to you guys but would the tensile load rating on the bolt in your drawing be less than if you shifted the bolt halfway up the face?
In Breezy's drawing the bolt (obviously for the physical limitations of fitting into a 45-50mm deep piece of wood) is halfway up the wall & not much wood above it, my money would be on the neck pulling those two small slivers of wood above the bolt shafts out once the strings are tensioned up. As you say though, if you did away with the gap under the extension & the fingerboard sat tightly along the surface of the top it could change the dynamics a bit.
By the way, I hope you aren't sitting watching that paint dry!

[Trevor Gore]

The paint's dry (enough) now!

No more answers? It's not that loaded a question!

[jeffhigh]

Crushing at point A or stretching of the connector bolt or yield at the anchorages.

But this is made worse because Breezy is trying to fit this into a total body depth of 38mm minus about 6mm top and bottom leaves you about 26mm to make the joint. So you will end up with the bolt centre not much more than 16mm below point A at most

[Nick]

Crushing at point A or stretching of the connector bolt or yield at the anchorages.

But this is made worse because Breezy is trying to fit this into a total body depth of 38mm minus about 6mm top and bottom leaves you about 26mm to make the joint. So you will end up with the bolt centre not much more than 16mm below point A at most

That's what I was trying to convey in my rather non focussed comment Jeff, thanks for conveying it more sucinctly
Doesn't leave much between point A & the bolt centreline & once point B starts seperating the joint is all but useless.

[breezy]

Crushing at point A or stretching of the connector bolt or yield at the anchorages.

But this is made worse because Breezy is trying to fit this into a total body depth of 38mm minus about 6mm top and bottom leaves you about 26mm to make the joint. So you will end up with the bolt centre not much more than 16mm below point A at most

So this venture is pointless and I should just glue it in?

[jeffhigh]

Crushing at point A or stretching of the connector bolt or yield at the anchorages.

But this is made worse because Breezy is trying to fit this into a total body depth of 38mm minus about 6mm top and bottom leaves you about 26mm to make the joint. So you will end up with the bolt centre not much more than 16mm below point A at most

So this venture is pointless and I should just glue it in?

I would, If I found bolts from the back aesthetically unacceptable.

[Nick]

Crushing at point A or stretching of the connector bolt or yield at the anchorages.

But this is made worse because Breezy is trying to fit this into a total body depth of 38mm minus about 6mm top and bottom leaves you about 26mm to make the joint. So you will end up with the bolt centre not much more than 16mm below point A at most

So this venture is pointless and I should just glue it in?

The glued joint is a tried & true method& has served Gibson well for many a year but that's not to say we can't re-invent the wheel to something better Breezy .

[Trevor Gore]

Crushing at point A or stretching of the connector bolt or yield at the anchorages.

Jeff has it exactly right, of course. I would expect the crushing at A to be the primary problem. How much force there is at A depends on the connector pre-load and the bending moment. And how much pre-load you have to put on to prevent separation at B under the bending moment depends on the separation between the connector and A; the more the better as practically everyone has said. So it comes down to how much separation is possible.

If the part called Neck Block in Breezy's initial sketch is left full height, I reckon the maximum separation between A and the connector centreline that you could get is getting close to 30mm (using a full width 10mm bolt bar let into an open slot on the back of the neck and a pair of M6 HT fasteners). There could be more separation if the 6mm cap is additional to the 38mm rather than included (my Strat has a 45mm body thickness, so 38 is on the thin side). To prevent crushing at A, you could inlay some brass bar, both sides of the joint, using the harder material to redistribute the stress concentration and so achieve a higher load before failure at A.

My guess is that you would now be getting close to a joint that would survive string loads and playing (provided you weren't planning on doing any back flips on stage) but it would still be rather fragile and not very robust.

But as others have said, if you don't really need a detachable neck, glue is a good option.

Back to that painting...