sdsollod wrote: Todd,
I just got through your posts on the acoustic guitar forum. Fantastic work! ...and it was very gracious for you to share all of that. I do have a question... How can one screw hold all that pressure? ...and how can a threaded insert not get ripped out?
Thanks again,
Steve
Thanks, Steve!
The short answer to your question is: it's strong enough, it works. I might not have thought it would unless I'd seen guitars made with very similar neck joints (Rick Turner, Laurent Brondel), also relying on one bolt to keep the neck on. So, I knew it could be done. With my variation of the design, I've done several things that augment the strength of that bolt and insert and the whole structure. First, the grain direction of the heel means the threaded insert goes into solid side-grain, not end grain. Second, I wicked CA in around the threaded insert. I'm not sure what it would take to pull that out, but I'll bet it's several hundred pounds, at least. I would guess it would take even more than that to rip the bolt out of the insert - both are steel, steel is dang strong stuff, and the threads are reasonably coarse (20 tpi, if I recall correctly). The way the neck block is made means that the bolt head bears against end grain, which is a very hard surface, and I've also put a large washer under the bolt head to spread the load, so I don't expect any significant wood-crushing to happen there. Nor will the bolt head rip out a chunk of wood, or otherwise break the wood of the neck block, because that end grain section is backed up by the main section, which is made of birch ply. The whole neck block is also solidly braced in place by the "axial strut" (that ginormous CF-wrapped dowel spanning the two end blocks) and the ipe-capped longitudinal brace going down the center of the back -- note the foot on the neck block that bears on that brace. Bottom line: I think the whole thing is an amply strong structure.
The joint between the heel and the neck shaft would be by far the weakest link if it weren't for the CF-wrapped dowel embedded in there. Take another look at the photos of the heel construction if you're not sure what I'm talking about.
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