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For those who use a mortise and tenon on your instruments, can you tell me what width and length M&T you use? Thanks in advance.

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Hey Chris, I've been consistent with 3/*4" wide 7/8" high (into the body), and it depends on the body depth at the neck joint, but usually I make the length 1/2" shorter than the body depth at the neck joint.

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I'm the same as Rod. I use a barrel nut these days just as a point of reference. The ones I use are slightly over 3/4" wide so I have to grind a little off the width.

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Tenon 18mm wide, 15 mm long, 10mm mortice cut into the heel block with a 3/8" brass or aluminium bar inside the heel block, bolt holes tapped to 6mm. (Trevor Gore style)

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I also use barrel nuts which are 20mm x 10mm making my tenon 13/16"x 1" x 3.1875. I don't do a standard tapered heel so I can get away with extra width.

Thanks, Michael. I was about to ask if the barrel nut (cross dowel ?) was driving some of the tenon height.


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"Cross dowel" works for me

I'm not exactly clear on which dimensions different people think of as width and length, but on my necks, the barrel nuts determine the tenon width (thickness?) as 1/2". The length that the tenon extends into the head block mortise is 3/4". The bottom of the tenon is 1/2" from the heel cap and the tenon is a three-layer cross grain laminate.

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Thanks for the input. Keep it coming.

For clarification: width= trebel to bass direction, length= fingerboard to heel cap direction.

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Width .75”
Depth about .80
Length depends on the guitar. I end the mortise about 1/4” above the bottom of the guitar.

I use barrel nuts and have to shorten them slightly so they won’t protrude on the edges. I do it with a simple jig on the belt sander.

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3/4” wide x 1” long x 3/4” less than the neck block is tall.
Tenon is initially cut to 1/2” wide then 1/8” added to each side in a cross grain direction.
I use a tenoning jig on the table saw which makes for a quick and painless process.
Also using barrel nuts which are +3/4” and need to be filed down.
I cut the neck block mortise with a dado blade on the table saw, doing a few feet at a time, then filling in the bottom with 3/4 x 3/4” block, making for a square M&T rather than the routed round bottom I normally see. This way I have a handful made up for the future.

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3/4 x 3/4 with a 1/2" dowel drilled into the depth to prevent splitting.

I keep the length about 1/2" less than the total height of the neck heel. I use 3/4" wide (total) with 1/16" veneers that run vertical or "cross" from the neck grain. I think that was in an article by Cumpiano, so I copied it. I use barrel nuts that I have to grind also.

I'm wondering why people are grinding their nuts (barrel that is). Why not make the tenon width the same as that of the barrel nut?

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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

If you use a tapered heel anything over 3/4' does not leave much space for the taper and undercutting for fitting.

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Ok, that makes sense. I make my tenons 1/2" wide and use use barrel nuts that are 1/2" long so no grinding is needed.

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For the survey, we use 0.780" thickness by 0.935" long tenon with 10mm diameter x 1/4-20 x 19mm length barrel nuts. The mortise is milled to 0.785" x 1" depth. Width of the heel is a real concern, as the heel on a tenor or other narrower necked instrument can be just a bit wider than that.

The issue with a Cumpiano-style neck joint is bearing failure at the edges of the barrel nut, and the ability to get sufficient gluing area to make the cross-grain reinforcement a meaningful hedge against that type of failure. The nominal 3/4" width allows us to use 0.063" x 0.400" epoxy/carbon fiber unidirectional material in slots centered on the area of the tenon outside the 5/16" holes for the 1/4-20 neck bolts, doubling the bonding area and avoiding too much of a reduction in neck wood to effectively transfer the barrel nut loads to rest of the tenon.

A current student building his #2, a Size 5 tenor, found that fitting the tenor neck with the wider tenon was much more difficult than his earlier 00-sized six string's neck joint. Using a butted joint was discussed as an option, but those skinny heels - even with dowel reinforcement - have very little meat to hold threaded inserts. As a consequence of those issues, the boss is looking at a narrower tenon - Mr. De Rocher's 1/2" tenon is close in size to the 0.566" thickness being examined - reinforced with 0.030" x 3/4" CF inserts and 9/32" access holes...this configuration appears to provide reasonable resistance to bearing failure on paper, so we will likely prototype it and have it tested at a local university's aerospace structures lab to verify that the joint will stand up to repeated cycling, as well as damage events where the joint is loaded in excess of the service requirement.

Worth mentioning that a dovetailed joint avoids the issues with narrow heels entirely, although there is the additional skill set required to fit the joint after the neck angle is set. I'd like to get through another two or three score neck resets before I suggest that that skill set is easy to develop!

Edited - 0.030" CF is what is being looked at...

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Using a 3 or 5 piece laminated neck reduces failure at the bearing surface of the barrel nut.
At least that’s my theory.

B

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My memory is so good, sometimes I remember things that never happened.

1.25" wide and 1.125" deep

One other point I didn't mention, I have gone to the 'improved Cumpiano neck joint. That's the one that uses barrel nuts And a piece of hardwood glued to the sides of the tenon with the grain oriented so the barrel nut is not pulling against endgrain.

There is photo at the bottom of his article: https://www.cumpiano.com/an-improved-neck-body-joint

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Joe Beaver
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