Dovetail v. Bolt (my long experience)

[tippie53]

This is a question I heard many times . A bolt on dovetail is not a joint that would be all that feasible. Look at the dovetail joint and as you insert the neck to the block, the lower it goes the tighter it gets . The neck in essence is pulling the cheeks of the dovetail out and on the neck block cheeks. Using a bolt will pull the joint the other way. That would want to pull the joint apart and separate the joint surface.
A dovetail joint is a simple and basic pinch joint. It is a traditional joint and one that has been used a long time. This is a pure wood joint . Simple and effective.
A bolt on joint is a mechanical joint and will rely on a machined fastener ( bolt and insert ). The joint will work but there are 2 pitfalls on this. The bolt can loosen but is easy to tighten. If you use this as a glue joint as Martin does , the glue surface faces are in shear , unlike a dovetail joint that is in compression.
Will they work ? Sure , is one better than another ?? If the joint is done properly yes, if the joint integrity is weak so will the joint.
Shimming a dovetail is common practice to reset a neck so it is a non issue. I like that fact that the joint is in compression . A proper dovetail joint can be strung up without glue. A bolt on while can be unglued will rely on the fastener.
So If you bolt on the dovetail , it is a bolt on joint no longer a dovetail as the bolt will work opposite of the dovetail mechanics.

[rienk]

Maybe we're talking two different ways of bolting on the DT neck.
There is at least one way to install a bolt on a dovetail which allows the bolt to actually draw the dovetail further into the slot. One way would be through the heel block end. Another way would be to install bolts inside the box, but at an angle (say 45 degrees) so that as you tighten the bolt(s), it draws the neck down (though it also brings it forward, which may not be a good solution). A final way would be to use bolts in compression instead of tension, so that it is pushing against the neck?
Just some top of mind ideas, and definitely not thought through thoroughly, let alone tested.

What about an upside-down dovetail? Meaning that the neck is actually slid in from the bottom, so that no bolts or adhesive need to be used at all (though a bolt could be used as a safety), as even minor string tension would keep the neck from being able to come out?

I figured that after 100 years of using DT joints, something like this would be used if it works.
Please point me to any threads that already discussed this, as I couldn't find any.

I just like the idea of using a Dove Tail joint that does not have to be glued down.

[tippie53]

you would be surprised what the passed builders have come up with. If the joint is done well the bolt is not needed.

[rienk]

you would be surprised what the passed builders have come up with. If the joint is done well the bolt is not needed.

I am hoping to learn how one can use the joint so that the "glue" is not needed.

[tippie53]

Unless you are bolting it in you need glue. With the dovetail There is the sliding dovetail that martin used and was a mechanical joint that allowed the neck to be raised and lowered. I will tell you that a dovetail unglued would not be practical unless you are making it a sliding dovetail
What are you tying to do with the joint ? That may help us understand your thought process . I have seen many different styles of neck joints . Some builders from a long time ago were very forward in their thinking

[rienk]

Unless you are bolting it in you need glue. With the dovetail There is the sliding dovetail that martin used and was a mechanical joint that allowed the neck to be raised and lowered. I will tell you that a dovetail unglued would not be practical unless you are making it a sliding dovetail
What are you tying to do with the joint ? That may help us understand your thought process . I have seen many different styles of neck joints . Some builders from a long time ago were very forward in their thinking

My hope is to build a cantilevered neck (fretboard) like used on cellos, and McPherson guitars.
Even if the neck joint is glued, the fretboard would still be suspended above the top.

I like the idea of using a removable neck, but prefer a dovetail over M&T ("The dovetail neck joint, which is all but abandoned by modern guitar makers, carries a certain low-mid tone that is hard to capture with a bolt-on neck" AmericanSongWriter.com).

I like how the dovetail is a friction joint, and am under the impression that it does a good job transmitting vibration and tone between the body and neck - without the need for additional mechanical fasteners (like the MT). However, if it's going to be removable, it needs to use fasteners to ensure it doesn't come loose - even though in theory you could play a guitar with a DT neck with no glue/bolts.

A bolt through the back (in the heel block) would be an easy solution, but of course, visible and thus not as clean aesthetically. A compression bolt on the inside of the box in the heel plate might also work, but it would rely on friction and not be in tension or shear.

I may have to settle for a MT joint, but was wondering if there is a way to accomplish this with a DT.
But one of McPherson's patents talks about how his neck bolts are angled so that they pull the neck tighter into the joint - which only seems to make sense to me on a friction joint like a dovetail. Attached is a screenshot of his neck cut in half (interesting that it doesn't seem to use the bolt angle concept in his patent).

[tippie53]

the mechanics of the dovetail are not as simple as the mortise and tenon. The Dovetail joint is a pinch joint , where the cheeks of the heel are pulled into the joint by the cheeks of the tenon. The only way a bolt could be used is if the bolt was pulling the neck down into the joint.
If you are using a bolt at that point the simple mechanics of a tenon would be easier. I don't think you would see a difference tonally.

[rienk]

I really like the concept of the Taylor NT neck, though I haven't heard anything great about it from players who seem to have lots of experience with many guitars. And our local repair shop says it is has no real advantages. it seems to have obvious advantages for mass production, but I think their custom shop uses DT?

I recall that Martin had an adjustable neck angle device for a while, but that the metal used didn't allow for as good of tone as the straight DT joint? (I'll need to break out the Martin book and verify).

I'm all for using the latest and greatest innovations - as long as it improves the sound and usability (or at least, doesn't detract from it).

[rienk]

the mechanics of the dovetail are not as simple as the mortise and tenon. The Dovetail joint is a pinch joint , where the cheeks of the heel are pulled into the joint by the cheeks of the tenon. The only way a bolt could be used is if the bolt was pulling the neck down into the joint.
If you are using a bolt at that point the simple mechanics of a tenon would be easier. I don't think you would see a difference tonally.

Do you know of any studies that compare the two?
My understanding is that the more contact area between the wood in the joint, the easier/better the vibration energy will transfer between the joint. With good joints of either type, this may be immeasurable...

With my cabinetry DT fixture, I haven't found the joint to be "too" complicated, and as simple as a guitar is (meaning, only one straight tenon, instead of multiple at ninety degrees) it seems to have benefits.
But again, I have yet to find someone who uses it along with bolts instead of glue... I assume for good reason (I'd just like to know what it is).
Presumably, such questions don't flummox a traditional builder :)

[tippie53]

There have been a few studies but nothing that was too scientific. In most cases the joint is a joint. The glued joint is stronger than the bolted joint but when it comes down to it , in both cases they sufficient for the job.
The dovetail in a guitar neck is different than the drawer dovetail . Martin is now using a simple dovetail to replace the mortise and tenon on the 16 and lower series. I can't say that it is an improvement .
There are many ways to do things. As far as guitar joints are concerned, the joint integrity is more important than anything.