Replace old ply back with solid wood?

[John Damon]

That’s why I’m here, I’m here to learn! I’m gluing the side lams back together now, then I’ll finish removing the braces. I don’t think they will be re-usable, so it may be a while before i can get some delivered. Meantime, I’ll clean up the old glue and fix anything that needs it. When brace material arrives, what size(s) will I be making them? What shape?

[Barry Daniels]

I make my braces 1/4" thick. I glue them onto the top and then carve them to shape afterwards.

You will need to remove the bridge plate too.

[Alan Carruth]

Ends of braces between the neck and the bridge need to have some height, to counter the down force os the bridge torque. Those need to be supported at the ends. Below the bridge the braces can taper out to nothing if you want, but if they don't, for whatever reason, those will neen to be supported as well.

1/4" wide bracing seems a little narrow for such a big box; I'd go to 7mm; just under 5/16". The upper transverse brace above the sound hole can be wider' the extra glue surface helps there.

I often say that the upper end of the top, is al about structure and has little to do with sound, while the lower end is all abourt sound and has little to do with structure. That's not altogether true, but it's not far off. The top bracing, and top thickness, can be reduced from the upper block to the lower one to improve both sound and strength, up to a point.

The critical area for stiffness seems to be between the bridge and the sound hole. Once the top collapses there you've lost it. The most common brace systems, X-bracing on steel strings and fan bracing on classicals, both concentrate bracing in that area.

[John Damon]

I’ve ripped the soundboard. It’s fixable. But DAMMIT! I hate that I’ve gone this far in the wrong direction

[John Damon]

Removed bad bracing. Left two that can be trimmed and still work. New bracing being fitted. Will not glue untill I get a yea or a nay from you guys.

[John Damon]

These haven’t been shaped yet, just wondering about height, width, and placement

[Barry Daniels]

How tall are they? The placement of the braces looks pretty good but I recommend the following modifications: I would have the two tone bars extend a little further, but not all the way to the kerfing. Also I would taper the ends of the tone bars and the finger braces where they contact the X-braces. You don't normally want them full height there because that will make for a stiff top. Even the two braces near the sound hole should be tapered on the lower ends and they should also be a little further away from the sound hole (like no closer than 1/4 to 5/16"). The tone bars look a little tall

[John Damon]

Ok, how’s this?
My x-braces are 7/16 wide and 7/16 tall, I shaped. The tone bars and fingers are 1/4x1/4, shaped.

[John Damon]

Shaped a bit. 1/4” wide, except for the joint. There it is a bit wider and left flat on top

[John Damon]

And these guys…

[Barry Daniels]

I would use a small finger plane and make some long tapers on just the lower legs of the X-braces and the tone bars. There is still a little excess meat there. And the finger braces are still a bit meaty too as well as the sound hole braces. Also don't forget to move the sound hole braces back away from the hole.

I assume your X-braces are 5/16" wide, not 7/16", which should be fine.

[John Damon]

Thank you!!!

[Alan Carruth]

The X braces seem low to me: mine usually end up around 9/16" at the high point. 7/16" wide is pretty beefy, but width isn't as good as height for stiffness. The stiffness of a brace goes as the width and the cube of the height.

[Barry Daniels]

Yeah, now that Alan mentioned that, I usually have the center joint of my X-braces 5/8" wide. In order to bring the height up a bit, an option not involving replacing the braces would be to add an 1/8" thick strip on top and then carve and sand it into the existing brace shape. However, I don't know if your narrow brace tops would allow this mod.

[John Damon]

Latest. Glue down the bridge plate and then the back? Or is there more to do here?
Here’s a picture of the plate for thickness reference. It is 1/8” pauduk

[Barry Daniels]

Too thick. More like 0.090". Also cut off the tip that runs up to the X-brace intersection. I take it back to where it is about 1/4" above the top edge of the bridge.

[John Damon]

Got it. I’m on it

[John Damon]

The pen is the line of the strings. Thickness is .090”. Removed tip to 1/4” past bridge. Bracing look ok?

[Alan Carruth]

You could taper the front and back edges down: the only part that has to be full thickness is where the ball ends of the strings are. I like to have both the front and back edges of the bridge plate out past the edges of the bridge, but tapered out as thin as I can get them to minimize stress risers. I normally glue the bridge plate down before the braces, which makes tapering the edges easy to do.

[Karl Wicklund]

FWIW I find this an extremely interesting and instructive thread.