OM Guitar Back Braces

[bearskindrum]

Hi all, what do people think about the the shape of the lower two transverse back braces on an OM?,,,The Scott Antes LMI PL34 plan calls for two 19mm wide x 6mm high braces while the Robbie O'Brien DVD suggests making them all 6mm wide x13mm high for reasons unexplained?? This is my 2nd OM build and while I made all the braces the same (6x13mm) on the 1st build I would be keen to hear from some of the more experienced builders what they do and why??...maybe it makes no difference ??

Regards Mark

[tippie53]

The Antes plans are way over build but on the back braces they are close to what the old OM was.
The upper 2 are 1/4 in so you should be 6.4 mm wide 13 mm hi
on the lower 2 they used 9.5mm by 19 mm on the old it was 19mm wide and 9mm hi.
so you should be just fine. They have a 15 foot radius on the back about 4.6 meter

[ruby@magpage.com]

A couple of weeks ago I bought a 1934 Gibson L-00 for the princely sum of $41. Problem is that someone had punched through the back. However, this allowed me to get inside and measure the bracing and seeing this has changed my thinking. Check the picture - the top bracing is 3/16" at the base, a little big if 1/16" at the top, and 9/16" tall, including the "X". The back braces are 1/2" tall and a little wider, but no where near 1/4".

Ed Minch

[tippie53]

that is on a gibson What are the brace sizes on the L00 you have Ed, It would be nice info to have. Also getting a shape of the cross section. You can do this with play dough and wax paper. Lay wax paper over the brace and squish the play dough over the brace. Makes for a quick look see.

Martin uses a different brace patten and shape. Also the Gibson braces a slightly different profile. The OM is a Martin model
Still it shows that about anything will do the job , backs are not as much of a working plate like a top is. The guitar you got for $41 is a great deal and now you can document that brace structure. Martin changed the back braces about the mid 1980's from the lower 2 braces that were more low and flat , to the higher brace we see today. The woods stiffness is in a math cube to the height. Width doesn't ad as much to the equation as one would think.
Post more details of that Ed , it sure looks like a nice way to get good information.

The antes OM print is based off a Martin design but I think there were liberties taken to the actual shape and brace structure. Maybe for legal reasons. I used that print early in my building and soon found they were just too tight for me. Once I got hooked up with martin I had the honor of access to the actual production patterns.