CF rods for headblock stabilizing

[ken cierp]

Gosh -- maybe a "Rainsong" could be used as a canoe paddle? They are total CF construction. And Martin's aluminum guitar -- a good tanning reflector? Its so much easier being unique when the music is a not a consideration.

[Dave Bagwill]

Here's a long vid of Rick Turner in his shop. The first few minutes, he plays his uke - he's pretty good, and then moved on to bass and other stuff before getting to acoustics at around 9:35. I wish he was a better player, you can tell that guitar has a lot more to offer.

Interesting that he gave his reason for the raised fretboard - so that humidity, which could cause the top go up or down, would not affect the fretboard.

http://youtu.be/o5D0BThSZIk

[Dave Bagwill]

From Mike Doolin: re; my question about cf rods as headblock support.

I think this is generally a really good idea, especially for cutaway guitars. When I initially designed the double cutaway, it was obvious to me that I’d have to do something to recover the strength of the upper bout. Over the years I tried several different bracing systems for the neck block. For the first few guitars I used a “Spanish foot” style neck block, where the foot extends all the way to the first back brace, plus two heavy braces glued to the top running diagonally between the neck block and the waist on either side. But I wanted to free up more of the top and back to vibrate, so I came up with the “bow tie” braces that went into most of the guitars I built -
(see doolin1 and doolin2 below) (In reverse order: doolin1 is at the bottom)

The braces are 3/16” thick mahogany with two layers of graphite cloth and a mahogany veneer laminated on both sides. They’re let into slots in the neck block and glued to the sides. The graphite makes them extremely rigid for their weight. In the second photo you can also see the solid Spanish cedar block I put in against the upper cutaway. It’s glued to the neck block, sides, top and back.

My thinking here was to prevent the neck block from rotating forward, while clearing the top and back with the bracing. The bow ties are the same thickness as the kerfed lining. If you look closely you can also see that I cut a little ledge in the tail block so its gluing surface is also the same as the linings.

This system worked quite well, and I used it in a lot of guitars. But I got to thinking that the bow ties weren’t the most efficient way to prevent rotation of the neck block. So I later came up with this more minimal brace:
See doolin3

The braces are 1/4” x 1/2” graphite bars with mahogany laminated to them so I have something to glue to. The key point is that they’re let all the way into the neck block and the pillars at the waist. They don’t touch the top other than within the neck block. In effect, as the neck block tries to rotate forward under string tension, the braces push down on the pillars, which obviously can’t move. This seems to work just as well as the bow ties, but is much more discrete (you can barely see them through the soundhole), and easier to make as well.

I did use graphite tubes in the Jazz Harp Guitar -
doolin4,5

But there I wasn’t concerned so much about rotation of the neck block as I was about compression of the top, since the instrument has a tailpiece. The string tension translates to compressive force between the neck block and tail block, and the tubes directly bear that compressive force.

All of this is to say, that I think graphite tubes bracing the neck block is a great idea, but I do think they work better when they’re inset deeply into the neck block. When they’re just butted up against it, there isn’t as much preventing the block from rotating forward. This is especially true if the tubes go to the waist, since they’re bracing at about a 45 degree angle to the force being applied. When they go to the lower bout, they’re more in line with the force. I used rectangular bars because they’re easier to glue tightly into a notch cut in the neck block.

But in general, I think _some_ sort of neck block bracing is a good idea, even for non-cutaway guitars. And for cutaway guitars, it’s an even better idea.

Thanks to Mr. Doolin - he's really generous with the information and the pix.

[John Parchem]

From Mike Doolin: .. , but I do think they work better when they’re inset deeply into the neck block. When they’re just butted up against it, there isn’t as much preventing the block from rotating forward. This is especially true if the tubes go to the waist, since they’re bracing at about a 45 degree angle to the force being applied. When they go to the lower bout, they’re more in line with the force. ...

This is a better description of the structural concerns I had when I viewed the first set of examples you showed. Earlier I was writing up a description of the efficiency of a brace to take a load is proportional to the cosign of the angle of the brace relative to the load. I think I wisely deleted that description.