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I PM'd Grant and asked if he was game for some discussion of his adjustable neck joint, and he said sure. Here's a photo of it. It's wonderfully simple - basically just an ordinary bolt-on mortise and tenon joint with a shop-made spring at the lower bolt. The upper bolt is tightened up first, then the lower bolt is tightened until the neck angle is right.

The sides are cut out to let the neck heel in, just the thickness of the sides (if you want to see a pic of that, I, or Grant, could post one). That's enough to allow all the necessary movement of the neck without showing a gap. That's a feature I like as well; much as I respect and admire the work of builders whose adjustable neck designs feature the hardware exposed, rather than hide it, that's an aesthetic choice that would not be my own.

Obviously, the fretboard extension support just floats in a cut out area of the top - with the fretboard tongue itself just barely off the top.

Grant, please correct me if anything in my description of your joint is incorrect, or elaborate on it if you'd like.

Now, here's my question for you, Grant. It would seem that this design would allow some movement of the joint as the spring compresses and rebounds (however slightly) with the oscillation of the neck and body as the guitar is played. It would seem that this would have a negative effect on the sound. Can you enlighten me on this? Have you observed anything in the sound of your guitars made with this joint that would even hint at a loss of power or tonal quality as a result of this "springy" joint?

Thanks!

   Todd Rose38818.8845949074

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

I wonder if that joint has a solid contact point near the top of the heel, close to the fretboard where it may act as a hinge. Then the only flexable point would be the heel and that, it seems to me, would be a non-issue concerning the absorption of energy from the strings. As long as that high contact point, which is pretty much in line with the pull of the strings, is rigidly supported the neck seems well designed.

[QUOTE=Todd Rose]

Now, here's my question for you, Grant. It would seem that this design would allow some movement of the joint as the spring compresses and rebounds (however slightly) with the oscillation of the neck and body as the guitar is played. It would seem that this would have a negative effect on the sound. Can you enlighten me on this? Have you observed anything in the sound of your guitars made with this joint that would even hint at a loss of power or tonal quality as a result of this "springy" joint?

Thanks!

   [/QUOTE]

In this joint, the spring is just providing preload for the bolt. The stiffness of the joint (if you're trying to open or close the gap) is the same as the stiffness of the bolt in parallel with the spring. And, the bolt is very stiff in tension and compression (maybe a hundred or a thousand times stiffer than the spring).

The bolt provides high stiffness to the joint even if you're pushing down on the neck (trying to close the gap) until you completely overcome the spring preload and unseat the bolt. Until that point, the joint will be quite stiff.

And, you would have to overcome not only the spring preload, but the additional preload of the strings, that are also adding to the tension in the bolt.

You might even be able to leave out the spring entirely, and rely on the string tension, but the neck would be really floppy until you strung it up.



Phil

[QUOTE=Phil Marino]
The bolt provides high stiffness to the joint even if you're pushing down on the neck (trying to close the gap) until you completely overcome the spring preload and unseat the bolt. Until that point, the joint will be quite stiff.

And, you would have to overcome not only the spring preload, but the additional preload of the strings, that are also adding to the tension in the bolt.

You might even be able to leave out the spring entirely, and rely on the string tension, but the neck would be really floppy until you strung it up.


[/QUOTE]

I follow you, Phil, and that makes sense to me... sort of. Thinking of the structure as a static thing, it makes sense. The string tension pulls the neck upward with a great deal of force and so the bolt stays seated and everything is solid. EXCEPT that when the guitar is played, now everything is moving. Among the many modes of vibration in the instrument, one is that entire guitar is oscillating lengthwise, like a long bar from headstock to tailblock. In the middle of this "bar", you've got a joint that can pivot (at the upper bolt area of the neck joint). The question, as I see it, is whether the energy of that oscillation is strong enough to slightly compress that spring in there, slightly unseat the bolt, and thereby diminish the solidity of the joint as things are in motion.

I understand you've got string tension always pulling the neck up, even while things are oscillating... I'm just not sure how it all actually plays out. Maybe the string tension is always strong enough, in combination with the spring's force, to keep the bolt firmly seated even when everything is oscillating... but I wonder. After all, it is the rapidly _changing_ tension of the strings in vibration that is (at least in part) setting the "bar" into oscillation... maybe the energy of that changing tension and resulting oscillation could wobble that joint at the pivot point in spite of the presence of the spring.

Physicists, engineers, what do you think???

Then again, the ultimate proof is in the pudding. Grant, does it work? Is there any loss that can be heard? Have you done any tests like replacing the spring with a washer and comparing the sound?     

_________________
Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

Todd,

Have you seen those acoustic guitarists that use the neck of the guitar for the whammy bar effect by pulling on it backwards and forwards? Notice how quiet it gets as the bottom bolt unseats slightly? No - me neither.

Seriously though I think that I would have had to have been wearing my "bo-boats" from a very early age to preserve my hearing to such a degree that I could audibly detect what you think may be happenning. I've said this before but I'm looking forward to the "Star Trek" technology that lets you attatch a neck to a guitar body by electo-magnetic force. I bet that if a guitar was made with such an attached neck with an air gap between the neck and body everywhere (under the fingerboard included)it would sound great.

_________________
Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

First of all, Thanks Todd, for starting this. I have been meaning to show this, but have been running too much to find the time.

OK, I can see your concern. However, this joint is way more solid than you might think. The top bolt is torqued down very tight. You could probably leave everything else out and be fine to play. I should note that the bevel on the end of the neck tenon which allows for the adjustment starts at the lower edge of the top bolt hole, so above that there is a square fit for tightening the top bolt. The total amount of adjustment that I build in for the bottom bolt is one complete turn after it is snugged up. With the 1/4 x 20 threads on the bolt, that is 1/20". This will drop the nut almost 3/8". But to do this, you really have to crank on the allen wrench, and you hear creaking and groaning while doing it

The key to this joint is to make sure that the neck angle and alignment is dead on from the get-go. Don't rely on the adjustment feature to compensate for sloppy fitting. Inletting the neck heel through the sides is exacting work, but actually quick and simple. Since there is no glue in any part of this joint (the fingerboard extension floats), removing the neck to make fine tunings to the fit is simple. Or a take-down guitar for travel

As for the sound, there is NO detrimental effect from this joint. These guitars are extremely loud and uniform regardless of the vigor of playing. Though I am not sure how much of a contribution is due to using white spruce tops or my "strange" bracing system.

FWIW, I should have a test CD of my latest using this joint(the cocobolo with the wild figure back) by the end of the week. If someone would show me how to post this as a sound file, I would be happy to do so. Or, since I am not computer literate about those kind of things, I would be happy to send a copy of the CD to someone with the ability and inclination to do so.

I will dig through my files this week and find a few more photos to illustrate some other details of this. I welcome any other specific questions.

GrantGrant Goltz38819.7875462963

The joint idea looks great to me. I think you might benefit by moving to a fine thread - 1/4-28.

I think something to hold the bolts from twisting due to vibration would be important - lock washer or a mild thread locker like Loctite 222, 242 or 248 perhaps.

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

[QUOTE=SteveS] The joint idea looks great to me. I think you might benefit by moving to a fine thread - 1/4-28.

I think something to hold the bolts from twisting due to vibration would be important - lock washer or a mild thread locker like Loctite 222, 242 or 248 perhaps.[/QUOTE]
Problem with fine thread is that the hardware is not readily available. The standard 1/4x20 seems to work fine. Typical adjustment is about 1/8 turn. Remember that drop at 12th fret is only half drop at nut.

Nothing is going to loosen from vibration here any more than a bolt-on neck will fall off. The bolts are very secure as is.

Grant

Just a few more photos. Also, somewhere I have a sketch drawing of this thing, but have not been able to locate.

These photos are from a full scale mock-up that I did before trying this on a real guitar.


Here is the whole thing ready to assemble. At the top edge, the shoulders of the neck seat firmly on the face of the neck block and the end of the tenon from the top bolt hole up seats firmly on the end of the mortise. Starting about 1/2" from the top, the face of the neck block along side of the mortise bevels in to allow the neck heel to pivot inward.


Here is a view of the inside after assembly showing the modifications of the upper end bracing. Since there is no downward pressure on the top from the neck extension, the upper transverse brace can be scaled down. This one is only 3/16" thick by fairly tall. The two "A" braces along the soundhole seat in notches under the corners of the neck block. They pass through cutouts in the upper transverse brace.


Here is a view of the outside of the joint showing the fit of the neck heel into the sides. I just fit things together with a completely sanded neck heel and scribe along the edges with a utility knife. I deepen the cut and remove the side pieces with a small chisel. Then do any cleanup with a small file. The whole thing takes about 15 minutes. One important thing, the sides of the neck heel need to be straight for the thickness of the sides plus a bit more so the joint does not open up if the neck heel is adjusted inward. Do leave a uniform gap the expected thickness of the finish on the neck heel.

Hope these photos are useful

Grant

Hi Grant,

The photos and additional explanation are very useful. Thanks. I'll take your word for it that the joint works with no detriment to the sound. Like I said, the proof is in the pudding, and it sounds like the pudding you've made is mighty yummy.      

One specific question I have: what did you make that little spring out of?

I wonder if the joint would actually work just as well, sonically, if there wasn't the flat area at the top of the tenon - if it were designed more as a real pivot point. I'm not suggesting you change your design, I'm just thinking outloud about how I might modify it for my own purposes. Maybe the solidity of it doesn't actually depend at all on that flat area, but would work just as well if it relied entirely on string tension and the spring to keep the lower bolt firmly seated and therefore allow no wiggle in the joint. I think I may try a variation of this joint on my next pair of instruments (one of which I hope to build with some wood we've discussed ). I figure, if the joint turns out to be at all lacking in solidity with the spring in there, I could replace the spring with a shim of some sort, like a washer perhaps. The neck angle could still be adjusted with relative ease by taking the neck off and putting a different thickness of shim in there - a very quick and easy neck reset.    

_________________
Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

Todd, I make the spring out of .035" carbon steel bandsaw blade stock. I actually described and illustrated the entire process on my buildoff guitar thread on the other forum. Go to "the buildoff threads" and look for "whitespruce". That's me. The spring sequence will be on one of the last 2 or 3 pages.

As for the flat spot or not, try what you want and if it does not work, you can always glue on a bit of wood and make the flat spot or whatever. That's another beauty of the system. You can modify it as much as you need.

BTW, I resawed some wood today

Grant

I am just finishing my first guitar. I included Grant's adjustable neck feature. Just for an extra dollop of fun, I used Grant's technique on a compound cutaway. So, it can be done, by a complete rookie.

I wish I could say I'm a great player and played the hell out of Grant's guitars, giving them a thorough test. But in truth I'm forever an advanced beginner as a guitarist, and when I was at Grant's, we were too darn busy for me to play much. I played on a couple of his guitars for a couple of minutes. The neck joint does not move. (I mentioned in another thread that I don't know how much to attribute to the White Spruce tops Grant used, and how much to attribute to Grant's bracing pattern, but the punch of his guitars was remarkable.)

I'm no engineer, but when I looked at Grants adjustable neck design, I could not see any need or use for the spring at all. (Grant has said it may not be necessary.) So, I'm not using one.

Also, my thinking was just like Todd's, and I decided to make a single pivot point between the bolts. I figured that unless the pivot point could be crushed, if both bolts are tightened (even with an air gap above and below the pivot), the neck cannot move. Wood would have to crush for the neck to move. So, I put in a pivot point, using Katalox for the pivot point and for the bottom of the mortise pocket. Alas, my tenon was too long, and I removed the Katalox pivot veneer from the tenon, and shaped the tenon as Grant does. But, I'm convinced it would work just as well.

Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

[QUOTE=Grant Goltz] ... If someone would show me how to post this as a sound file, I would be happy to do so. Or, since I am not computer literate about those kind of things, I would be happy to send a copy of the CD to someone with the ability and inclination to do so.

I will dig through my files this week and find a few more photos to illustrate some other details of this. I welcome any other specific questions.

Grant[/QUOTE]
Hi Grant,

I would be happy to show you how to upload and post the sound file, and/or I will host the MP3 or WAV on my site if you want.

I also have some photos of your mock-up from various angles, if anyone wants to see some specific feature.

Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

Grant, thanks for the info on the spring.

Dennis, that's a very interesting variation you came up with. Different from what I was imagining, actually. But I like it. Now the wheels in my head are turning again in a new way. Good stuff to think about while I'm on vacation this coming week. Oh, wait, the plan for the vacation is to have some time away from constantly thinking about guitars...

At any rate, I'm dropping out of this conversation now because I'm hitting the road with my family tomorrow. We'll be on a mountainside in West Virginia, in a little cabin... no phone... no computer... just one guitar to play, none to build...

Thanks, everyone.

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

Well, I have the CD's. They did 4 tracks. The first is each individual string plucked and allowed to decay, the second is strummed chords (E, A, G, C, and D) each allowed to completely decay, and two tracks of playing. These are just straight miked with absolutely no processing. They also did a second CD with two tracks that each starts out totally clean, then a bit of EQ, then a bit of compression, then a bit of delay, and finally with all three. Dennis has offered to help me get these up so folks can hear.

As for any detrimental effects of the neck joint, both Matt (my friend who did the playing) and the guys at the recording studio had nothing bad to say. They loved the sound. One thing that totally blew them away is that none of them had ever experienced an acoustic guitar with so much sustain. Guess maybe that suggests that nothing is being lost due to the adjustable neck joint

Grant

Can't wait to hear that guitar!