Help me understand mortise and tenon neck joints

[Wrnchbndr]

I say tomato, you say tomato... I haven't mastered the skill of making a traditional dovetail in my own construction. I really appreciate you folks letting me play in your sandbox as I am primarily an electric guitar maker with some limited success in applying what I know toward shorter scale 8 string instruments that are tuned like a mandolin. Getting back to the original post, string tension stress on a mandolin seems to be significantly higher than a guitar or a violin so it follows that measures are justified to employ a stronger joint and the fear of going through all of the work of building an acoustic instrument only to fail while trying to execute a dovetail joint prevents me from taking the leap. That said, I have seen quite a few skinny, and seemingly inferior joints function adequately. With instrument repair as my primary mode of income for twenty years, I can't say that I've seen any difference in the number of failed mortise and tenon joints to failed dovetail joints. I am in awe that violins don't simply fly apart. I think its likely that if you use good wood, good glue, integrity in your application of skill, and intuition, the choice of joint becomes secondary.

[Buck]

...And Martin used to use a straight mortise and tenon on all the series below 18. They have now switched to an “improved dovetail” which is actually still a sort of mortise and tenon, not a true traditional tapered dovetail. A lot of people don’t know that there is actually a screw in that joint. The screw head is hidden by a wooden “plaque” on the heel block. I guess my point is, I don’t know of a straight M/T that uses glue only with no screws or bolts...

Martin used the mortise and tenon (M/T) neck on all guitars below the Standard Series starting with the D-1 in the early 1990's. This changed in 2012 with the introduction of the Simple Dovetail, which is really just a straight dovetail fitted by CNC. From there forward Nazareth production of those guitars use the Simple Dovetail, while models made in Mexico still use the M/T neck.

One correction though, the Simple Dovetail does not use a bolt in construction. The brass insert seen in neck dovetail is used for a hanger attachment during finishing, but there is no bolt there when the guitar is built. (That brass insert is all modern Martin necks for use during the finishing process.) Simple Dovetail guitars use the same neck block as the M/T guitars, so there is still a wooden cover plate, just no bolt. The M/T joint does use a bolt, and while the official response is that the bolt is only there as a "clamp" while the glue dries, my experience tells me it's a vital part of the structure.

Side note: In Martin terms 18 is a Style not a Series, as their use of Series defines structure. They've muddied the waters a bit on that point in modern times though.

[V70416]

my carlson-signed gibson monroe model has two bolt-ish things
in the neck block area. is that considered a mortise tenon joint?

i admit i felt a little let down when i learned it was not a traditional neck joint;heck,
i didn't know any better.
but after 26 years of regular use there have been zero problems of any kind.

i'm not a builder but enjoy eading about construction of instruments. thanks to all for sharing
your knowledge and experiences.

[multidon]

v70416- yes, that is a mortise and tenon joint with two bolts and glue as well. That is a very strong joint and I don’t believe you will ever have to worry about it.

Buck- thanks for the clarification on Martin’s.

[Tom Haywood]

Just a little more on specific instrument joints. I went to the violin shop today and looked at some open violin neck joints while I was there. The tenon on the violin neck, if you look down from above, is very slightly wider at the end of the tenon than at the beginning. The same corresponding shape of the mortise means that when the neck tenon is slid down into the block mortise, the neck cannot be pulled straight out the end. It stays in place in all planes except from the top. The "bird tail" shape, although very slight, combined with the fixation in the mortise fits the definition of a dovetail joint as I understand it. I'll add that the shop owner asked: "Why wouldn't you call it a dovetail?"

I also looked at a Saga "V" neck joint (aka Siminoff joint) which I saw on their lowest line Kentucky mandolins about a year ago. It is not quite a true tenon in my view, because the neck taper fits the block mortise, i.e. you would have to consider the entire neck to be a tenon (although you might make the case that it is a shoulder tenon of sorts). Interestingly, there is an extremely slight taper of the mortise from wider at the interior of the head block to narrower at the rim (slight bird tail shape), which corresponds to the slightly narrowing shape of the neck heel. The result is that the neck can be pulled almost completely straight out the end but not completely. Until the two dowel pins are inserted. Then this joint is very strong and stable in all planes - with or without glue. So I would have to say that the full "V" joint used in mandolins, which includes the wooden dowel pins, also fits the definition of a dovetail joint as I understand it.

So, both of these work without the need for nails and screws; the violin joint requires glue - at least to hold the top and back button on; but neither one is a straight mortise and tenon joint so they are not really germane to the OP's question.

While there, I also looked at a 1985 Taylor dreadnought guitar that was open for brace repairs. The two big bolts holding the neck on appeared to create a perfectly stable joint after all these years. But it caused me to wonder about the sound transmission through all that metal, similar to the discussions about metal adjusting screws in mandolin bridges.

[Marty Jacobson]

Metal is great for transmitting sound! Isn't it?
We have mass, which we know has negative effects on tone (or at least absorbing effects), and stiffness, which is generally positive.
So metals are quite dense, but extremely stiff. Which one wins? I made several reproduction Gibson mandolin bridge parts a few years ago. They got good reviews.
BTW I think Tom is an amazing person and builder, I am just asking hard questions.

[Larry Simonson]

Sorry this tread has been mostly about the definition of a dovetail joint. This diversion started when I wrote "mortise/tenon joint like used on violins" was challenged. I stand by what I wrote.

[pops1]

The difference as I see it is not the shape of the joint, but the shape of the sides. Mortise and tenon has straight sides, dovetail has tapered sides. A violin neck joint has tapered sides, not straight, hence (for me) a dovetail,

[Tom Haywood]

Sorry this tread has been mostly about the definition of a dovetail joint. This diversion started when I wrote "mortise/tenon joint like used on violins" was challenged. I stand by what I wrote.

I think this discussion took a left turn after post #5 where Don implies that dovetail joints are not mortise and tenon joints. I'm not sure that he meant that implication, but it brought up what appears to be that view held by some. Don hit the "Thanks" button to your post, so it seems to be a welcomed turn. I'll paraphrase my violin store friend and ask: "Why wouldn't you call a dovetail a mortise and tenon joint?" In my mind it is clearly a type of mortise and tenon that has certain advantages over other types, just as the other types have certain advantages.

[multidon]

Tom-if you will re-read my post in #24 you will see that I state “technically a dovetail is a type of mortise and tenon” so obviously I’m aware of that and didn’t mean to imply otherwise. As for hitting the thanks button, I’ve done that to a lot of folks on this thread, simply because I think it’s been a lively and interesting discussion. I like that!

On the other hand, we have gone off the rails a bit. Originally I really wanted to know if a builder used a straight mortise and tenon, I mean straight on all sides, no taper in any direction, for his neck joint and simply glued it, with no screws, bolts, or dowels, would it be strong enough for the task? Or would it be doomed to eventual failure?

If it is strong enough, why does Weber use bolts? Does anyone know what kind of joint Collings uses? Does anybody know why so many builders seem to not be upfront about the joint they use, and they don’t list it in their specs? I’m re-asking some of my original questions hoping we can get this train back on the rails.

[Buck]

...Originally I really wanted to know if a builder used a straight mortise and tenon, I mean straight on all sides, no taper in any direction, for his neck joint and simply glued it, with no screws, bolts, or dowels, would it be strong enough for the task? Or would it be doomed to eventual failure?...

Mechanically, I don't like the idea of a straight tenon, glue, and no bolt. I'm sure it's been done successfully, but I don't think it's the best way. A well fitted dovetail will hold without glue. A bolt will hold without glue. I don't like the idea of glue alone. Some mechanical support seems much better to me. I don't know of any major builders (factories or individuals) who routinely use a straight tenon and glue only. Of course, someone here might enlighten me. There are a good many things I don't yet know.

...If it is strong enough, why does Weber use bolts? Does anyone know what kind of joint Collings uses? Does anybody know why so many builders seem to not be upfront about the joint they use, and they don’t list it in their specs?...

See above on Weber. I suspect they feel the same way I do. While I've owned mandolins of both neck types, and still do, my 1999 Weber Big Sky is still my #1, and trouble free since I purchased it new.

Collings uses a dovetail on mandolins, but bolts on guitar.

I'm guessing it's not a critical issue to many buyers, so makers don't list it.

[jim simpson]

I'm following and enjoying this this thread. I have owned various mandolins over the years that utilized the various neck joints, I was not too concerned to the type as long as I liked how the instrument performed. Now, to veer slightly, I wonder if any builder has attempted a neck to heel approach like the banjo/dowel stick method. It seems that the top, sides, & back could be fairly free to vibrate although I guess the top is the most important vibration surface? Thoughts!

[HoGo]

Collings uses a dovetail on mandolins, but bolts on guitar.
I'm guessing it's not a critical issue to many buyers, so makers don't list it.

Collings uses mortise and tenon on mandolins (or should we call it dovetal for reasons some violin makers call their joint dovetail as the sides of the tenon likely follow edge of fingerboard as splay a tiny bit?):
Watch here:
https://youtu.be/MWbtytUnOKs?t=138

[Buck]

Collings uses mortise and tenon on mandolins (or should we call it dovetal for reasons some violin makers call their joint dovetail as the sides of the tenon likely follow edge of fingerboard as splay a tiny bit?):
Watch here:
https://youtu.be/MWbtytUnOKs?t=138

The neck joints in the video appear to be traditional dovetails. I didn't see anything that would suggest otherwise.

[VernBrekke]

There were several reasons why Weber used a mortise and tenon joint on their necks with machine screws and barrel nuts:

1) The mortise and tenon blanks/bodies were much easier to cut consistently for batches of necks and bodies.

(my observation, based on my time spent maintaining the dovetail cutter for a guitar factory, is that a dovetail joint is best used when a builder shapes one neck and fits it to one body in a relatively short period of time. When you cut a bunch of necks and a bunch of bodies and let them sit for any length of time, the joint fits are going to be all over the place. Some pieces of wood shrink, some expand and some don't change much at all. Manufacturing processes can compensate by controlling the humidity, changing the cut tolerances, leaving excess, etc. but it's harder and takes a higher skilled employee to compensate for mismatches with a dovetail than a mortise and tenon - without doing a bunch of shimming that is...)

2) The screws act as a clamp and hold the neck in position until the glue dries. They also give structural support throughout the life of the instrument.

3) By using two screws, one high and one low, it was easier to do minute adjustments to the neck fit to get a more accurate neck angle and, as a result, more consistent bridge heights.

4) Because the mortise and tenon joint is made of generally single, vertical cuts, it is easier to maintain the correct vertical angle of the neck to the body than a dovetail with it's multiple matching angles (the top of the fretboard parallel to the top of the body). An incorrect neck angle affects the angle of the bridge by making one side of the bridge tilt higher than the other side - which degrades the performance of the bridge.

We never considered using the mortise and tenon joint, without additional support for the glue, for the above reasons.

[Tom Haywood]

To the actual questions.

1) Is a straight mortise and tenon without hardware or dowels strong enough to work on a mandolin? My experiments tell me it's not and that it is the wrong joint for the purpose. I was taught that glue should add only a little extra strength to a joint. The glue should not be relied on to hold it together. The only reason I can think of to use a straight mortise and tenon joint, even with hardware or dowels, is to save time/money. It takes me about 8 hours to do a Gibson style dovetail, and about 5 minutes to cut a straight M&T joint. It makes neck resets easy? How often do you see a mandolin that needs a neck reset? Far more often, I see necks separating from the body. Why invite that problem by using a joint that can't hold itself together to begin with?

2) If it is strong enough, why does Weber use bolts? Maybe the Webers will join this discussion.

3)Does anyone know what kind of joint Collings uses? I have not repaired a Collings, so I don't know.

4) Does anybody know why so many builders seem to not be upfront about the joint they use, and they don’t list it in their specs? I'm having a little problem with this question about builders not being up front, but I understand that it seems to be this way. The "V" ("Siminoff") joint makes the most sense to me in almost every way, and I would use it on all my mandolins, but I don't for two reasons. First, it doesn't sound as good to my ear as the Gibson style dovetail. Second, concerned buyers who are willing to spend the price of a decent mandolin want a "dovetail". It's the industry standard for an upper level mandolin. I think most people buy based on brand name, and some folks will accept whatever the brand is making available in the buyer's price range as being reliable. As a small time builder, the only thing I've been able to sell is dovetails. I have tried to think of ways to disguise a "V" joint to look like a dovetail (without success), but I wouldn't advertise the joint as something other than what it is. I am hesitant to advertise that a mandolin has a "V" joint because I won't get any calls, but I don't have any problem discussing it with a potential buyer because it has so many advantages. I have to accept before I even build it that I'll probably have to keep it.

It is important to me to know what kind of neck joint I am buying in a stringed instrument. If the builder/manufacturer plays hide-the-ball, I won't buy their instrument.

[Tom Haywood]

Verne posted while I was typing. Thank you for a clear and concise explanation about the Webers.

[Bill McCall]

There were several reasons why Weber used a mortise and tenon joint on their necks with machine screws and barrel nuts:

1) The mortise and tenon blanks/bodies were much easier to cut consistently for batches of necks and bodies.

(my observation, based on my time spent maintaining the dovetail cutter for a guitar factory, is that a dovetail joint is best used when a builder shapes one neck and fits it to one body in a relatively short period of time. When you cut a bunch of necks and a bunch of bodies and let them sit for any length of time, the joint fits are going to be all over the place. Some pieces of wood shrink, some expand and some don't change much at all. Manufacturing processes can compensate by controlling the humidity, changing the cut tolerances, leaving excess, etc. but it's harder and takes a higher skilled employee to compensate for mismatches with a dovetail than a mortise and tenon - without doing a bunch of shimming that is.

......

4) Because the mortise and tenon joint is made of generally single, vertical cuts, it is easier to maintain the correct vertical angle of the neck to the body than a dovetail with it's multiple matching angles (the top of the fretboard parallel to the top of the body). An incorrect neck angle affects the angle of the bridge by making one side of the bridge tilt higher than the other side - which degrades the performance of the bridge.

We never considered using the mortise and tenon joint, without additional support for the glue, for the above reasons.

Interesting, as I would think repeatedly machining that join (tenon) would be easiest with a single end tenoner rather than sawing with a fixture. And you’d be coping for the body as well, even if that took a slight bit of fitting. The fitting of the neck block to the sides, ie, dead square and vertical, seems to be something to be overcome with ‘minute adjustments’.

My 21 year old Absaroka has held up just fine.

[Jeff Mando]

In terms of a woodworker's or carpenter's definition, a dovetail joint and a mortise and tenon joint are two very different things. Simply do a Google search and click images and you can see the difference. Quite different.

In terms of guitars for example, a Martin or Gibson acoustic uses a dovetail neck joint. A Les Paul, Les Paul Junior, or SG use a mortise and tenon. Using the guitar examples, both joints are fine for there intended purpose. As a repairman, I would say acoustic guitars need necks reset more often than electric guitars, but I won't say the neck joint is the only contributing factor.............

Not saying how or if this relates to the tension a mandolin neck joint is subjected to.

[HoGo]

The joints you can see in the Collings video are esentially the same as the "Siminoff" V joint without the dowels. I don't know if they use bolt as well or just glue it.

The definition of dovetail is quite blurry. There are various definitions in dictionaries (that are often way too loose or even partially contradict what cabinet makers would tell). I'd rather listen to cabinet maker than dictionary.
Here is one that I think comes close to the essence of the matter as any other (Merriam-Webster):

: a flaring tenon and a mortise into which it fits tightly making an interlocking joint between two pieces that resists pulling apart in all directions except one

Looking at this definition only straight (non- tapered) dovetail would qualify as tapered dovetail allows more than JUST ONE direction to pull apart. Straight dovetail can be pulled just up but and is tight all along the ride (MUST be done perfectly) but tapered dovetail allows slight angle (it loosens from the body as you go up).
The typical mandolin tapered dovetail has the property of interlocking and resisting pulling apart (by the normal string pull) when inserted tightly but allows approx. 15° off the perpendicular direction for disassembly (that's why it is much easier to reset than straight dovetail)
The V joints (and typical violin neck joint is esentially the same thing) do have slightly flaring sides (because the fingerboard/ neck get wider towards body) but not enough to resist pulling apart (IMO). It will hold together to some degree but would not qualify as "interlocking" to me. Really tightly cut straight tenon will hold together by friction as well...

If you asked me which joint is the best I would tell the one that will hold the neck tightly for the life of the instrument (not being abused) and will provide more resistance if slightly abused. As additional bonus I would add easy reset if needed for future repairs (you never know when someone breaks headstock or neck and you need to pull it apart...)
With these criteria tapered dovetail would be at the top, the next one would be straight tenon with bolt(s). And after that straight dovetail and the last would be V joint without dowels.
Why? The tapered dovetail is strong, easy to disassemble and leaved more wood of the body block intact. The straight tenon would leave the neck block strong and the bolt(s) would add the additional security to the glue used. Also would be easier to pull apart when needed and reset. Straight dovetail is OK joint but can be PITA to disassemble even if you steam it (imagine pulling the swollen wet fuzzy pieces of wood tightly fit against each other all along the dovetail). The V joint is last as it removes much wood from the block leaving just thin pieces at the edges that can break off if side force is applied to neck (think dropped case) and if you remove neck these thin sides can deform and show ugly scars after reset while on the above joints the shoulders of the joint cover the ribs and make the joint cleaner.
The V joint is BY FAR the easiest to manufacture so most of the (CNC-using) factories do it...

Soundwise I don't think there is any difference (if the joint is solidly made and well fitted). I've played mandolin that had V joint and bolt for 20 years wit no problem. But in my mandolins I only do tapered dovetail.