Double top bracing

[Barry Daniels]

It's not only for support but for allowing the string vibrations coming through the bridge the travel through the braces and activate various areas of the top. At least that is the concept. Not having the bridge sit on the braces isolates them from the string vibrations to a degree.

If you feel like your top is quite strong already, instead of moving the x-brace to a non-traditional location, I would suggest just installing light and smaller x-braces in the normal position. I use x-braces in my flattop guitars that are about half the cross sectional area of Martin x-braces.

[Randolph Rhett]

I'll repeat that I don't understand why, if all you are worried about is the collapse between the bridge and the neck block, you don't just go with parallel braces. X-braces add a component of stiffening the cross-grain, which is not relevant to you. Parallel braces are specifically for the issue you are facing.

[Eldon Howe]

Randolph, you said .X-braces add a component of stiffening the cross-grain, which is not relevant to you. Parallel braces are specifically for the issue you are facing.

Do you think that x braces are not relevant to my top because of the altra thin wood and nomex core in non directional?

[Randolph Rhett]

In short, yes. You are thinking of this top as if it were a piece of wood. It really isn't. Wood tends to be much weaker in cross-grain than long-grain. On a wood top, you might shore up the cross-grain to get a more consistent stiffness with an x-brace. As far as I know you could have laminated the spruce veneers 90 deg from each other.

Your top is already roughly the same stiffness in all directions. You have probably seen classical double tops that have no bracing. The point of the double top is to have an ideally stiff surface in all directions without the bracing.

You are not adding bracing to mold the tone but rather to shore up a weakness. I think that you are having collapse in the top between the bridge and the neck, not between the bouts. If I were you I would be trying to add as little bracing as possible to solve that problem and otherwise trying to leave the top as unmolested as possible.

Lest I sound too adamant, I've only been building double top guitars for about four years, and many of them aren't wood. My first tops had bracing. Bracing did NOT improve the tone. I do take steps with the CF to shore up some structural weaknesses caused by the sound holes. However, the less I glued to the front the better they sounded to my ears. As you can see from the pictures, I don't use any spruce bracing at all anymore.

That said, maybe x-bracing is EXACTLY what your tops need. If your gut tells you to brace it that way, don't let me dissuade you.

[Eldon Howe]

So this is it so far. The 16.25” lower bout arch-top guitar.
Double top 1mm spruce on each side of the Nomex core.
No bracing at this point touching the inner spruce layer.

The flying brace is a sandwich Spruce core/carbon fiber on all sides.
It is scribe fit to the bottom side of the top plate and it was then lowered 2mms
as that is what the top had dropped under full tension of all strings.

A temporary piece of scrape 1mm cherry wood is slide between the top
and the flying brace, where the most defection is.
After a week no further settling was observed on either side of the temporary cherry filler.
The green tape indicates possible parallel brace location.

I would prefer no bracing as well.

I could install parallel bracing as suggested, or replace the temporary cherry with a 2mm thick piece of spruce and slide it back and forth to find the sweet spot.

[Randolph Rhett]

I see you are trying a neck connection in the style of Ken Parker arch tops (in fact the whole guitar is inspired off that design). Can you share your neck build techniques? How is the post attached to the neck? Is it a CF neck or wood? How is the post insert into the neck block? Is it adjustable, if so how? What is the post made of?

Love to see what you have cooking there.

[Eldon Howe]

Highly inspired by Parker for this one off project.
The neck is a Bass wood core with carbon all around. Square carbon tubes used for neck post with a turn buckle in bedded within.
The double action truss rod is useless in this super stiff neck.

[Mark Swanson]

That's coming along great! I bet you are learning a lot from this one.

[Randolph Rhett]

Lots of questions on that neck join:

1) So the neck "tube" is a square CF tube inside a second square CF tube fixed to the neck block, or does the square tube insert directly into a square hole in the wood neck block (and bear against/slide past the wood of the neck block)?

2) How does the "tube" attach to the actual neck? Does it pass through?

3) Did you purchase or manufacture the square tube/s?

4) It there basswood inside the tubes?

5) What caps the tube that you have the turnbuckle attached to? How are the turnbuckles attached to the tube/s?

6) Do you use some kind of lubrication to keep them sliding past each other and not binding?

[Eldon Howe]

Lots of questions on that neck join:

1) So the neck "tube" is a square CF tube inside a second square CF tube fixed to the neck block, or does the square tube insert directly into a square hole in the wood neck block (and bear against/slide past the wood of the neck block)?
1) Currently this neck tube inserts down into the block and bears on all sides. I used flat pre made carbon sheets epoxied the carbon 4 individual wood block quarters and glued the 4 quarters together and fitted it as tight as I could to the carbon post.

2) How does the "tube" attach to the actual neck? Does it pass through? No!!!
2) the first short layer of neck carbon cloth was let down into the post tube, so a little cloth in the tube and a little on top of the cherry neck veneer. Additional layer of carbon on all four sides( inside tube) . Two vertical maple fillers were fit inside tube creating a center joint where another layer of carbon could run both vertical and become the first full layer of carbon full length of the neck. Two small shims in the vertical center joint completed the neck fill.
Two more more layers of carbon on the cherry veneer extending all the way through the neck to the peg head.
Then the bass wood core with useless truss rod.
Two more layers on top of the basswood and then the finger board.

3) Did you purchase or manufacture the square tube/s?
3 Yes

4) It there basswood inside the tubes?
4 no,maple

5) What caps the tube that you have the turnbuckle attached to? How are the turnbuckles attached to the tube/s?
5) just the maple. I used standard nuts one with reversed threads. I think a longer threaded insert would be better and have less knee action under a load. I can still change that on this neck if I wish.

6) Do you use some kind of lubrication to keep them sliding past each other and not binding?
6 yes but not really sure what is best

On the next build I'm thinking of having only two bearing points to reduce friction. one on the back side of the post just under the top plate and one in front of the post just above the bottom plate. Maybe a adjustable metal plate so the pitch of neck could be dialed in, so as the neck is adjusted for height it won't go out of tune. My first neck on another guitar goes a couple cents out of tune.

This might be a good topic elsewhere as this one is off subject for double-top bracing.
I would love help and good ideas on this whole neck joint thing as well.