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Are there any perceived benefits for making a tenon shorter (say 2.5" total length) or longer (say 2 3/4" length)?
A shorter tenon length would absolutely be quicker and easier to tweek, as the length is shorter.
~OM body with Martin style heel 14FTB~

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Measure Twice,

Karl Borum

I would be personally inclined to go with a longer tenon in the case of a hardware mounted neck to get the bottom bolt closer to the point of stress, and doubly inclined if it were a dovetail to get the tenon as close to the bottom of the block as can be.

That said, I doubt a 1/4” would make much difference either way.

Also, when fitting a neck, in my case at least when I did M&T joints, the tenon generally doesn’t get touched, it’s the face of the neck all around the tenon that gets tweaked.

With my method of work, I usually don't have to tweak the "pitch" much at all but do spend a fair amount of time on the "yaw" to centerline with a snug-ish fitting tenon. It was the same with dovetails- not due to the cheeks, but the tenon, evidenced by an excursion from the centerline.

With a snug M&T, if there is yaw, I remove material from both sides of the tenon (equal but opposite) and add equal and opposite shims to take up the small gaps from "yawing" the tenon sideways. It's not a difficult or complicated process but takes a LOT of time. Even if material needs to be taken from the cheeks to adjust yaw, material also has to come off the tenon (and equal but opposite shimming), if it is to stay snug. I wish to reduce that fiddling time with a shorter tenon, perhaps a pipe dream.

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Measure Twice,

Karl Borum

That seems tedious, lol.

Having a hard time visualizing how you are fine tuning. Probably because I do a butt joint and have no tenon to fuss with. In my method, Yaw is controlled completely by flossing the bearing surface of the neck to the body. Yaw and neck angle are both adjusted this way and at the same time. So when you say that you don't have to adjust the "Pitch" what I call "neck angle" at all, I have a hard time understanding what you are saying. If both sides of the heel are drawn in firmly to the to the body and the Pitch is correct AND the snug tenon is preventing Yaw to be adjusted, I don't understand what is happening.

Are you saying that the entirety of the heel is seating flush to the sides and the M&T is tight so you can't adjust the yaw? That would seem like the Yaw and Pitch are completely built in when the box and neck are made. If that is the case, then the bearing surface of the sides/rim must not be perpendicular to the centerline.

Or, is it that, because the Yaw is off, only one side of the neck heel is bearing on the sides and that one side is locking in the pitch?

If it is the first scenario, thinning the tenon from both sides would allow it to seat properly with space in the mortise. I suppose you could then shim to fill in. I'm not sure that I would bother to do that; but then again, I don't even use a tenon so I don't care if there is a space or not. For me the only area that has to fit tight is about an 1/8 of an inch all around the heel. All the rest of the endgrain is releived away to make flossing/fitting easier. The bolts just pull everything tight.

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Bryan Bear PMoMC

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

Team bolt on butt joint here too, lol.

There's no need for the tenon to touch anything except the bolts. M&T is essentially the same thing as butt joint except half of the heel structure is sunk into the body so the outer portion can be lower profile (which only matters if you have a cutaway, where it lets you keep your thumb on the back of the neck at higher frets). Give it some wiggle room so yaw adjustment is only a matter of flossing the heel cheeks.

I started making M&T neck joints with the StuMac plastic templates and recommended bit. I was actually kind of shocked by how loose the joint was. That got me to taping bearings to bring in an acceptable tolerance.

I still use the templates and bit for the mortise but cut the tenon (roughed out at least) on the table saw, of course leaving some meat for fitting. It is so easy to clean up with a sharp chisel, I don't think it takes any longer at all. I shoot for a slip fit, not snug.

I just measured one on the bench and the difference in the M and T fit is right around 0.010". I find a slip fit still leaves plenty of play to allow the yaw adjustment to be made with flossing. It is also tight enough to center the T in the M within 0.005" when all goes the way it is supposed to. I'm happy with that.

The tenon on this one is 2 7/8" from top to bottom but my bodies run a little deep too.

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Brian R, Wood Mechanic
N8ZED

Only reason I keep using a tenon is to hold hardware for the bolt on neck. Lets me make a slimmer heel then I could with a straight butt joint. I reinforce the tenon with two 1/8” slices of maple to hold the nuts. Like Dennis says, leave it a bit loose.

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Steve Smith
"Music is what feelings sound like"

With the fingerboard-deck flush with the top plate, I check and adjust for centerline first, with the tenon almost home, irrespective of the cheeks not bearing evenly on the sides. After neck is centered, I send the tenon home, where the cheeks contact the sides, then get both flush to sides with sand paper. Lastly, I adjust the neck angle. I keep all my joinery "tight", with firm slip fit on a guitar mortise and tenon. If the tenon is not "tight" in the mortise, and I don't mean clamp it in there tight, might just as well do a butt joint.

After posting this and reading the comments, I'm making 2 3/4 inch tenon length standard on my builds- I don't see any down side.

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Measure Twice,

Karl Borum

I've also found that the Elevate M&T hole guide requires a tenon minimum length of 3.042" to index (datum) properly to the top. THis is when using the male tenon of the jig to interface with the female neck block mortise. Another way to say this is that the jig is nearly 0.300" too long for a 2.75" tenon.

My side height at the neck block, including the thickness of the top and back plates is only 3.275" and I think a tenon over 3" long is too long for an OM body. Anyone care to chime in with similar experience on this one? I'm going to shorten the bottom of the tenon part of the jig by 0.300" with a hacksaw and bastard file. Now I know why they named them "hack" saw and "bastard" file...


The mod will not affect the overall function of the jig, it just allows it to register (sit flush) to the top with a 2 3/4" or longer tenon.

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Measure Twice,

Karl Borum

I like a M&T for the same reasons as Steve. Even a slip fit ensures adequate alignment and even more important is the added meat in the small cross section area of the short grain in a narrow slender heel to help prevent splitting and allows greater depth of threaded inserts.

I don't think I'll ever get past the fear of putting an insert in a slender heel with a cross section of ~ a square inch of short grain wood. I know lots of folks do it successfully but I look at it like a weak area I can nearly double the strength of with a tenon. Making life more difficult, I don't flatten the area of the neck joint either. Funny the things we choose to fuss over.

I just love the svelte look of that "spiked" heel.

Admittedly, a butt joint has plenty going for it on the production side and plenty of builders I respect the work of use it.

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Brian R, Wood Mechanic
N8ZED

Brian's point about increasing the cross sectional area of the heel by the addition of a tenon is good to keep in mind. Blows to the side of the neck torque the short grain of the heel, putting the grain there in shear. The more cross sectional area there is there, the more stress of this type that the structure will survive. Note that for acoustic guitars the body is not that massive, but the neck is long and so provides the potential for considerable leverage.

That said, for my own instruments I tend to using the bolt-on butt joint for flattop acoustic guitars and smaller instruments with low mass bodies, but will usually use a M&T joint for guitars with more massive bodies (like some archtops), and will always use it for instruments with longer necks and more massive bodies, like ABGs. I have not done any kind of testing on any of this. But taking the fact that the original Taylor and Godin joints were known to hold up well, the butt joint seemed to be robust enough. Far as I know all of my butt joint instruments have no failures here. The thing that got me to consider the M&T joint for basses, particularly ones with quite massive bodies was one time when I had such an instrument on the bench with the neck hanging off the front of the bench, and I ran into it while moving about the shop, snapping the neck off. Because the body of that instrument had so much mass it presented considerable inertia. I've been using M&T joints designed specifically to increase heel cross sectional area for ABGs ever since (and retrofitted that bass right away).

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R.M. Mottola
LiutaioMottola.com

Author of the books Building the Steel String Acoustic Guitar, Practical Design of the Acoustic Guitar and Similar Instruments, and Mottola's Cyclopedic Dictionary of Lutherie Terms.

I don't check in here very often. If you need to contact me the best bet is via email through the contact page on my site.

I'm doing the same thing, and no doubt picked it up here at OLF.
Next neck tenons, and forever more, will be with connector/ barrel nuts. I ignorantly cut the tenons a bit too shallow on my first two necks to accept the barrel nuts.

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Measure Twice,

Karl Borum

Another good reason to add long grain side supports to the tenon is to prevent the tenon from splitting under the load force of barrel nuts. I also found that adding a cap to the endgrain was sufficient for that cause.

Those concerned about the strength of a smaller heel with a butt joint can run a dowel through the heel vertically before drilling the insert holes.

There’s also the Gilet/Gore bolt on/bolt off neck joint design. I’m liking it so far.

Longer tenon with reinforcement, barrel nuts, and a loose fit for me. Center line adjustment with the undercut cheeks. Here’s a way to floss more accurately especially when adjusting the centerline. The slots in the plexiglass faux fretboard allow easier flossing.
IMG_0580 by Terence Kennedy, on FlickrU

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