Bracing an OM

[segovia]

Hi

I am following the Grellier plans for an OM, I have cut the X braces at a 28 degree radius. My question is what radius do I use for all the other braces - the T brace is also shown as arched, is it better to leave this flat ?

[johnnparchem]

On a steel string I radius the upper brace and then flatten it where the fret board will be. You can also leave it radiused and flatten the top where the fret board goes after the top is assembled and glued to the rims.

[segovia]

Thanks

I just noticed on these plans that two of the braces on the back are 19mm wide, seems unusual to me .

J

[johnnparchem]

Thanks

I just noticed on these plans that two of the braces on the back are 19mm wide, seems unusual to me .

J

Lots of guitars built with the two lower braces 3/4" wide. I have made them that way, I have also made them with 4 braces the same height and width of the upper braces. It is up to you.

[segovia]

Thanks

I just noticed on these plans that two of the braces on the back are 19mm wide, seems unusual to me .

J

Lots of guitars built with the two lower braces 3/4" wide. I have made them that way, I have also made them with 4 braces the same height and width of the upper braces. It is up to you.

Good as I already cut them (;-)

[tippie53]

These plans are not to bad actually. There are a few schools of thought on bracing. The key is the geometry of the top for the neck angle and the final set up for the string and saddle height.
Old school had only the top's main X braces radiused. All other braces were flat. If you want to radius the all the braces that is ok to just pick the style you want to go with. Personally I find I have more control of the geometry doing the X at 28 and all others flat.
The back radius can vary from 15 to 25 feet depending on the style , since the backs are a complementary to the top the braces are more structural than tonal. The lower wider braces on the backs lower 2 are a fall back to vintage times. They do tend to let the back participate more in the guitars voice but the trade off is the instability during RH changes.
I do use them on my own guitars and prefer them though the narrower modern braces , being higher are more stable and stiffer. Again a personal choice. Best advice is to build a few guitars and use the different brace schemes and pick your favorite. One thing to add to this is that joint integrity goes without saying , the better the joinery the better the final outcome

[segovia]

Great advice John, many thanks

There is also no support strip above the T1 brace on this design, is that personal choice again?

J

[Darryl Young]

That brace is optional as well. Old Martins didn't have it. IIRC, they made the neck block less deep and added the "popcycle brace" about the same time. I've read different opinions bt some say it was added to help prevent the top splitting along the edge of the fingerboard. Other ways to address this without the popsycle brace.

[hummingbird]

Old school had only the top's main X braces radiused. All other braces were flat

Hey John, I've always wondered about this. When glueing the braces onto the top, I would use the 28' dish to both sand the radius into the bottom of the braces and as a glueing caul on the bottom of my gobar deck when glueing them on as many people do. However for the braces that you leave with a flat bottom would you still use the dish as a base while glueing or use a flat surface?

[tippie53]

Yes
the only braces I do in flat clamped is the transverse ( truss rod ) brace . That takes a good bit to flex.
As for the neck block sized pre 1939 the neck block was 1 9/16 thick , post 1939 they are 1 3/8 , this narrowing had some bad effects on the top along the edge of the fretboard and the Popsicle brace was installed. D Young got it right.
When I do the pre war I use the wide block .. In 1937 the traverse brace was 3/8 wide and 3/4 in high. Here I still like the 1/2 in wide brace and make it 3/4 high but shape it a bit different than the martin one.
Popsicle braces can be about 1/2 the size , all you need to do is add some support at the fretboard extension edge to help support for that shear force.