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The bolts pictured above do not have a flat head or hex head on the end to remove them. I suppose if they did then you could simply remove them through the sound hole.

Otherwise the bolts would be in the way.

Great thread as I'm looking for a different neck attachment than the insert machine bolt, butt joint system I now am using. Getting everything squared up or even getting the insert to go in square is a nightmare.

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I take it this is the difference between flossing by moving the neck on sandpaper vs moving the strip of sandpaper?


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I’m confused too, but I think he means that on a butt joint with inserts you can pull the sandpaper across the whole heel in one swipe, whereas with hanger bolts you are flossing one side at a time, like a M&T neck.

Is that it?


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I think that is exactly it. With the bolts in it is a little more annoying to fit sandpaper strips in and keep the heel cap even. With the bolts out, it is a little more annoying keeping the neck in position while you pull the sandpaper through. Inserts give you both options, hanger bolts allow for a slimmer heel.

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Bryan Bear PMoMC

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

Although most of our bolt-on necks are done with the Cumpiano improved neck joint, we did butted threaded inserts for the Style 42 guitars and hanger-bolts and nuts for bolt-on conversions. We use coupling nuts to make neck fitting easy on hanger bolt-fitted necks, as well as in combination with a standard nut to drive hanger bolts to depth. Most of the coupling nut extends out from the nut, so it's easy to tweak things for neck flossing and fitting. Also an option to use the crown nuts shown in Mr. True's post - those sized for 1/4-20 hangers use a 3/16" hex wrench.

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I have flossed insert-bolt necks by just loosening the bolt(s) from inside and flossing the two sides, alongside the tenon. I am thinking of using hanger bolts on my next one and anticipate being able to do the same thing. I have never tried a butt joint as it seemed like your bolt holes have to be right on or the neck can move side-to-side. Up and down is governed by the fretboard extension. I make my boltholes slightly oversized just for ease of assembly.

Ed

I used to use brass inserts in the heel. Now I prefer to use plain ole 1/4" hanger bolts and the 1/2" maple dowel. Simple,
effective and easy enough to source. I think any of the systems mentioned here should be adequate but over torquing
is often, imo the reason for failure.
As for alignment while drilling the M&T parts I use a simple jig to get a perfect fit every time. One of the many tips I picked up here
on the OLF over the years.

One of my greatest early discoveries that simplified many lutherie procedures from centering the holes for tuning machine screws to marking drilling points for bolt on necks was transfer punches. Couldn't live without em!

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Don't forget, the vector angle force from the strings is very low on the hardware holding the neck in place. If there's enough strength in the 180-220 lbs pull from the strings to shear the threads off a 3/16 bolt of any sort, I hate to know what the top of the guitar would look like...

With probably a couple 100 thousand guitars (or more) built by Collins with the hanger bolt, I think you can be assured in the trust of the use of the hanger bolt. The first guitar I built with the hanger bolt was in 2005 and the neck hasn't moved at all on that guitar, and it gets played pretty hard by a semi-pro player.

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And as far as flossing the neck heal, I do that before I glue the heal cap on. And with the relieved heal, only a 1/8"+/- of the heal is being sanded so it goes quick, especially if utilizing a neck angle jig to get it very close already. Once the neck is set perfect, I then can attach the neck to the body with a piece of 120 sandpaper between them (along the entire heal to keep the angle right) and I run the edge of the heal cap along the sandpaper to get the perfect joint between the heal cap and the body.
Remove the sandpaper, replace with wax paper and glue the heal cap on with CA glue. Easy peasy.

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"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

Flossing - Rather than floss with the neck in situ, I have a piece of thick MDF, with a neck mortise cut out of it. The MDF face is covered with 120 grit. The MDF is clamped sticking out from the bench and I floss the neck on that - it's more stable, if I want to floss one side, I tape over the other side with masking tape. I do this with finished necks too. Because I outsource my spraying, I don't have control over the amount of lacquer that goes on the body. A fraction of a mm more on one side of the mortise than the other can change your angles. So it's come in useful a few times. And no chance of scratching a finished buffed body.

Have to say, this has been a very useful, well-intentioned thread. Very enjoyable.

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nigel

http://www.theluthierblog.com

This.

Realizing there's anecdotal evidence that sometimes these joints fail, that doesn't prove that a hangar bolt or threaded insert directly in the end grain is some massive weak point in the system.

If I'm remembering my free body diagram stuff correctly: 220lbs at say .4" above the top of the neck/body joint gives us .033' x 220lbs or 7.26 ft-lbs, let's call it 8, of torque on the joint. That's not a whole lot. The resulting force at the 'bottom' bolt is even less due to the distance from the pivot point.

A doweled or cross pinned or whatever type of connection could definitely improve the survival rate for trauma but it's completely un-necessary to live a long life under normal conditions. This is borne out by the millions of guitars with just such a joint out there that are living long and happy lives.

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For in situ work or where the fretboard remains on the neck shaft and the neck area is less than uniformly flat, we put a single layer of packing tape on the guitar and the same with the sandpaper used for flossing. Besides preserving the finish (tape removal is easy with naphtha on older, less stable finishes), the tape reduces friction and reinforces the flossing strips enough to allow A weight papers to be used.

Mr. Birko's point is well taken. On threaded insert, barrel nut, or hanger bolt failure modes, the push/pull and rotational loadings due to string tension or use are considered - at least in this shop - to be well within the range of what the unreinforced (e.g., no cross-grain dowels; no carbon fiber inserts) joint can handle. The failure modes that we design for are the ones outside of normal storage and use...essentially unexpected handling events or commonly-seen accident events which create an impulsive load several times higher than what the unreinforced system can comfortably handle. As a repair/build shop, we see these sorts of accidental or rough handling-related failures on a routine basis (e.g., failures of Martin's original mortise and tenon joints and Gibson-style necks), so have taken note and provisioned for them with appropriate reinforcement.

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Interesting. I did not realize the forces were so low.

Years back when I made a testing rig for the unreinforced Cumpiano joint I did use a torque wrench and although I can't find my notes I think the failure was rather low, like 7+ ft-lbs or so. I always worried about an overly aggressive owner or repair person leaning on the bolts.

I do know that the reinforced tenon could not be broken before the jig started to deform. I use Maple strips now as it is a lot easier than carbon and plenty strong.

I do have a few unreinforced Cumpaino joints out there although I always did saturate them with thin CA. Have not heard of any failures.

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One of the interesting discussions we have had of late was on design requirements. Apparently, it is not unusual for designers to fail to identify requirements outside of the intended use scenarios which end up driving key elements of the design. One of the examples cited was that what determines the minimum thickness of aircraft skin metal on smaller aircraft is nearly always resistance to dents or puncture during handling on the ground (e.g., being pushed back into a hanger or parking spot by hand), versus the loads applied in flight or even in landing.

So according to what passes for wisdom in this shop, the things that a guitar has to do when it's not fulfilling its intended purpose are more likely to fix key structurally relevant design requirements like neck joint strength and stiffness than when the guitar is actually being played.

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- Bob Dylan

As a slight aside, since flossing has been brought up, I'll mention one plus of using a tenon that's glued into the neck (as described on the first page of this thread). Since making the tenon and installing it in the neck is a separate operation from cutting the neck end to fit to the end of the body, I don't need to do any flossing to get a perfect fit. Since the tenon is out of picture when cutting the neck end, that step can be done with a single cut and the neck set angle and skew angle come out on the money right off the band saw using a simple jig to dial in those angles. I don't missing flossing cheeks at all. I think this would work for butt joints too.

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On a body designed with a flat neck area or for block heel designs with parallel sides, that is likely true, but for curved bodies and heels with any taper, the cheek curves, so will not mate properly with the side without some fitting - either Mr. Forster's fitting off the body or in situ fitting and flossing. We used butted necks with the Style 42's, but with that gracefully curved body shape on the 12 fret Martins and the well tapered heel with slight recurve, the fitting was about as much work as a tenoned or dovetailed neck joint.

While flat neck areas and block heels make fitting easier, they are just not an option on most vintage work, although it seems like Taylor and some other manufacturers took that route to simplify their production methods and avoided a skilled fitting task before opting for their current neck design.

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- Bob Dylan

If you go back and look at my post about the "floating tenons" I use, you'll see that the neck area on my guitars is not flat. It's curved, which was the reason I came up with the idea of using a separate tenon so that I could cut the end of the neck to a radius to fit the curve of the body.

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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

I actually read your post with interest, Mr. De Rocher...I collect ideas and concepts like some people collect recipes, and while I've used floating tenons in furniture and for uke neck attachment, it was an interesting approach to the task. I suspect that what confused me was your statement in that post that the neck is milled to a slightly smaller radius than the body, which would seem to suggest a need for some further fitting.

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The neck end is cut at a slightly smaller radius to ensure that the neck won't be "high centered" when fitted against the body. It is also effectively the same thing that people do when they relieve the face of the neck end next to the tenon to reduce the contact area of the neck end with the body to just the side edges of the heel. On my dreadnought body, the radius of the body through the neck joint is 8". I cut the neck-end radius at 7 3/4". That introduces a gap in the center of the neck contact area of less than 1/32". Here's a photo of the neck and body of the guitar I'm building now.




You mentioned that tapered heels would pose a problem for fit. If the the radius of the body varied significantly across the neck joint contact area, then I can see how some adjustment to the fit could be needed to account for that. The end of the body on my guitars is a vertical cylinder of constant radius and I'm cutting the neck end as another vertical cylinder of constant radius. Because of that, it wouldn't matter whether the heel sides were straight or tapered. The edges of the sides of the heel see the same radius along their length whether they are straight or tapered.

I'm making the neck for my current guitar right now so I just happened to have some relevant materials lying around and I did a quick and dirty test. I have a radiused offcut from the end of the neck that has straight sides. The first photo shows the offcut. (One end of the offcut is thicker than the other. This difference corresponds to the set angle of the neck.) The second photo shows it in place on the guitar.




Then, I cut a taper in one side corresponding to a heel width of 1" and put in place on the guitar. Tapering it didn't change the fit.

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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

I do the same thing as you do Jay. Then when I am done flossing the whole of the heal is flush to the head block/sides. I've always thought that it would be important for sustain and tone to have a nice flush mount. But that's probably not true. Kind of goes back to the old bolt on VS dovetail joint but none the less it's one of those things that I don't give up on and it's good for the marketing department

The best sounding guitar I've ever played and owned was my 1890s How Orme. And If you've ever seen a Howe Orme neck joint, you'll understand that the solidity of the connection between neck and body is not as important as people imagine.

But you're right - from a marketing point of view the closer your views to your customers, the better. Even if they are wrong.

The Howe Orme neck joint doesn't need much flossing.

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nigel

http://www.theluthierblog.com

That reminds me a bit of the adjustable neck on a couple National archtops made in the fifties that I used to have. On those, the neck had a metal piece that extended down from the neck at the neck body joint and fit into a mortise in the head block. It had three allen screws arranged in a triangle that extended through the metal piece. The tips of the screws contacted face of the headblock. Adjusting how far those screws extended beyond the inside of the block made it possible to easily adjust both the set angle and skew angle of the neck. Pretty cool and there was no heel, just a plastic cover plate over the mechanism.

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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

Fascinating stuff!

Still pulling on the loose tenon thread, has anyone used Baltic or Finnish birch ply as the tenon material? It looks as though tensile strength would be close enough to SA mahogany (which is well in excess of needs) to work, but the cross-grain plies would essentially eliminate any chance that an unreinforced tenon or laminated tenon (e.g., Mr. De Rocher's three same-direction plies) could see bearing failure in a barrel nut/KD bolt joint, and would obviate the need to insert a cross-grain dowel to prevent the sort of thread failure seen in along-grain hanger bolt and insert installations.

I mention this because of the Ibanez Artcore 7 string archtop-to-electric oud conversion that has been dropped in my lap. I knew this sort of thing was coming (stay long enough and get stuck with one of the weird projects that walk in the door...it may be that this is a subtle prod to exit the nest), so this thread was timely.

We had a pre-'Summer of Love' Fender Kingman acoustic in for some work, and I have to wonder if the Fender design team did not get at least part of the solution right re: bolt-on necks (although I question the drain pipe between neck and tail block ). It seems like just about as much lumber went into that neck joint as in some modern bolt-ons in any case!

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For the times they are a changin'

- Bob Dylan