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That's a good point that there are other forces acting on the neck then just string tension... Two bolts it is!

Yes, the static load. For dynamic load, would you be thinking of an added load coming from playing the guitar?

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That’s what I use, works great. I could see getting a dedicated mortiser if I was making 20+ guitars a year.

At my current rate, the drill press attachment is fine - only need to drill one hole per guitar so the chisel rarely needs resharpening either.


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The more I think about the 1 bolt idea the more I am convince a second bolt is worthwhile. A single bolt in the low part of the heel would resist the strings pull trying to rotate the neck just fine. If the bolt starts to loosen, it will still be able to do a good job in that direction. But, if there is only one bolt, it starts to get a little loose and you inkowingly art it around by the neck and hang it from a strap, you are stressing the rest of the structure. A second bolt is a nice backup.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Not sure how easy it would be to calculate the input but yeah, I was thinking of the players who do the neck vibrato thing, loads if the guitar is dropped and so on. Probably just academic. The only guitars I've seen with a failed neck joint were in some kind of accident far beyond normal wear and tear.

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Steve Smith
"Music is what feelings sound like"

joshnothing wrote:
"at least theoretically, a round rod has somewhat of a wedging effect as the bolts are tightened. The concern being that it could split out the heel/tenon if overtightened. How likely this is in practice, I don’t know. "

I addressed that in a prior post: it's a real problem alright. I also spoke about the remedy.

I've been using only one bolt of late. The main issue I can see is that it might work loose, but the furniture bolts with the wide heads should resist that. We'll see.

Alan, what I took from your earlier post was that a tight fitting wooden dowel glued in place would not be an issue. My dowels need to be firmly tapped in with a hammer. I took your comment to be more about putting metal hardware in. I may have misunderstood.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Apologies Alan, I had misread your earlier post.

I too make the bolt bar a very tight fit in the heel - I find nominal 3/8” brass bar will not fit in a nominal 3/8” square mortise-chisel hole without some light filing - this let’s me sneak up on a good fit.

Regarding the chance of a bolt loosening, I follow Gilet’s recommendation and use a couple Belleville washers under the bolt head, in the hope it keeps the bolts preloaded if wood movement would tend to loosen things.

It’s cheap insurance, but for years I never used Belleville washers and I never actually experienced a bolt just working itself loose in normal service. Has anyone had that happen?

I like the furniture bolts too for their large head and if for any other reason they look good on the inside guitar. I would imagine for a loose square bar you could epoxy it in place and it would be super tight. That goes for anything. I typically have to use a hammer to get the dowel I use to fill the hole.

I have used the Cumpiano barrel nut with a reinforced tenon and furniture bolts the last 17 years. The only loosening I was aware of were one or two that got severely dried out. I was thinking the headblock probably shrunk.

That is probably flawed data though as have probably only seen maybe 20% ones out there back for follow up.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I guess we hope that since we're not hearing about problems, we're not having problems...

I had bolts loosen a bit on a very early effort. That one was most likely my poor workmanship at the time. I use the furniture bolts too and feel like there is probably plenty of surface area to help out. I haven't had a bolt come loose since. I have read several questions about loose bolts on Martin necks. I'm not familiar with that specific design but I think it is a single bolt. I also think that the bolt might not be intended to be the only connection. These might be glued as well.

So, my answer is yes and no. Yes, I have experience with bolts coming loose but no, not in my modern instruments. Yes, I have seen people discussing bolts coming loose but no, it is not first hand evidence.

Still, I'm pretty comfortable wasting a bolt and insert that may not be strictly necessary.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

I use hanger bolts and furniture style hex drive cap nuts. They've worked very well for me. Belleville washers can be used to help prevent the bolts loosening over time, but I haven't found them to be necessary at least so far.

Dave

Don't know if the Belleville washers are necessary, but I use them anyway.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Same here. I need to add the cross grain dowel to the mix though. Right now I’m putting hanger bolts with epoxy into the end grain and using the cap nuts.


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I had done hanger bolts in banjo necks for years, and with the addition of a neck tenon, I think there's plenty of meat there to hold even without the dowel. Could be wrong--banjo necks aren't under as much pressure as guitar necks, but at least so far so good.

Dave

A glued in dowel should be fine. What counts is the contact all around the insert. If the drilled hole is not tight around a cross dowel nut I flood it with CA. So far, no problems.

I have seen loose bolts on older Taylors, where they used a socket head cap screw.

One thing I like about the furniture bolts is that they use the same size Allen key that the truss rods I get do, so that you can cover both bases by throwing one tool in the case pocket.

Hopefully, all your customers are sharp enough to know the difference between the truss rod and a head block bolt. I'm pretty sure there are people out there who would look in the sound hole to see where to insert the truss rod wrench and see a head block bolt and then finding that the truss rod wrench fits it, think it must be the truss rod.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Good point; as soon as you make something idiot proof a more complete idiot steps up...

I had thought about that too especially since once on one of my very own guitars I was tightening the truss rod and it would not budge and I thought hmmmm... Then realized I was tightening a furniture bolt

So now I drill a little hole in the UTB just big enough for the right Allen key that guides it right to the truss rod. That's at least a bit of error handling.

Random thought: Why use metal hardware (threaded inserts, barrel nuts, Gore-style square bar, etc.) for the female threads in the first place? A lag screw into wood can hold plenty of tension. Glue a dowel vertically up the heel to provide some good grain to bite into.

Fair point and purely from a structural perspective it would probably work well. For me there is some aesthetic appeal as the guy building in a joint made with hardware I have at least some hand in fabricating myself, and custom made/fit to a specific instrument.

And then there’s the marketing side of things … I can’t see a customer getting excited about lag screws on a luthier-built acoustic guitar, many already have a hard time accepting anything other than a dovetail.

For whatever reason, end users of guitars have long since decided that neck attachment method (dovetail, bolt, long tenon, short tenon, through neck) is an element that they should think about when shopping for a new instrument.

I tell people all the time to buy the guitar that sounds and plays the nicest regardless of manufacturer, species of wood or construction method but few really take this advice to heart …

That would be hanger bolts. Lag screw on one end and, machine threads on the other, lag screwed into a vertical dowel.

True, they are almost the same thing. I was just curious why I've never seen the regular kind used. All I can think of is that wood is easier to cross-thread when screwing back into it, and not as wear-resistant as metal. But it only takes a couple seconds to find the existing thread, and it's highly unlikely that a guitar's neck will be removed enough times for thread wear to be an issue. Josh is probably right and it's just a matter of marketing. But I'd bet it's the terminology, rather than aesthetic. Taylor managed to make the term "bolt-on neck" acceptable, and hanger bolts can hitch a ride on that popularity, whereas lag screws cannot.

EDIT: Actually it looks like lag bolt is an acceptable term for them, so nevermind that reason. And I thought of a real advantage, which is that they'll stay in place even if the neck becomes a little loose due to humidity shrinkage or whatever, whereas metal hardware will tend to migrate down the thread unless it's fully tightened.

That’s true and at least round these parts Fender-style electric guitar construction is referred to as ‘bolt-on’ too despite the fact they’re clearly wood screws [FACE WITH TEARS OF JOY]