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Oskar,
When using a 24.9" scale length on an OM shaped guitar, all you're actually doing is building a OOO.
The difference in the location of the bridge between the two is less than 1/4" and it will present no odd
or even easily noticeable appearance in the two guitars using the same soundhole location.

I recently taught a week long guitar building class in which the student decided to switch to the 24.9"
scale from the original 25.4" scale and there was no need to change anything on the top including the
soundhole and rosette location. The guitar came out great as we reworked the bracing placement to
accommodate the shorter scale length.

It was exceptionally loud and responsive when we played the guitar for the first time and it had that
great softer feel that the lower tension of the shorter scale provides.

Regards,
Kevin Gallagher/Omega Guitars

Been there, done that. I'm finishing up my first guitar right now.

viewtopic.php?f=10122&t=22708

I intentionally made it 24.9" scale and unintentionally placed the soundhole where it would be on a 25.4" scale. consequently, all of my bracing is also 1/4" off. I've been told it will be fine. after much internal torment, I'm going for it, as the only alternative at this point, to "fix" it properly, is to rip the top off.

the placement of the bridge pin holes (so far, drilled for the low and high e) on my bridge plate looks like this:

http://photos-e.ak.fbcdn.net/hphotos-ak ... 0671_n.jpg

I'll have it strung up within a few weeks. if it explodes, or if it doesn't, either way, I'll post about it.

after I had discovered that this error ocurred, I spent some time in the "bracing library" thread at UMGF. one thing I noticed is that throughout the years, Martin bracing has sorta been all over the place. you will find both 000's and OM's that have the cross bracing barely nicking the edge of the bridge, and 000's and OM's that have the cross-bracing back-shifted so that the bridge is pretty dang close to the intersection of the "x." the variations are much more than even a mere 1/4". after I saw that, I wasn't so worried. it all "works," even though I much prefer prewar bracing to anything since. but I was still bummed out that I didn't get the intended situation that I was aiming for.

these are only our first guitars. i'm considering the intended, ideal situation to be a target for the next one...

_________________
"...you have to get over your strict adherence to your largely imagined notion of absolute perfection..."

I did something similar. 25.4" OM but I glued the fretboard on even with the headplate instead of leaving a 1/4" for the nut per the plan. Same result, my bridge moved 1/4" toward the soundhole. First thing I checked was the bridge plate but it looks ok - much like yours. I'm not real worried about it. I thought about trying to move the fretboard but with CF rods and all decided I'll do better on the next one.

_________________
Steve Smith
"Music is what feelings sound like"

While working at Martin back in the 90s, I saw many 000s come through the line with 1 3/4" wide
nuts and the typical 24.9" scale length. I also saw many OMs come through the line with 1 11/16"
wide nuts and the typical 25.4" scale length.

The chief designation that differentiates the two is the scale langth. Same body size and shape and
identical in almost every other detail, but the scale length creates the largest difference since each
can have any nut width.

An OM from Martin will always have a 25.4" scale length, but the newer 000s can have either a
25.4" or the traditional 24.9" scale length. During my time there, Martin was at the threshold of
introducing all of what are now their entry level guitars. That's when they decided that they could
make both the OM and 000 models at the entry level with their more common 15.4" scale.

Regards,
Kevin Gallagher/Omega Guitars

New to the forum and have made three acoustic (13 solid electric) guitars including an archtop. All sound terrific and all had issues. I believe that if you place your x-braces to properly match the correct bridge position for the scale, you'll be fine. Just do it. Build the guitar, enjoy it and make the next one. As Keith Richards, and many others have said, “Every guitar has a song in it”. You might get lucky and find many great songs in this new guitar.

FWIW, my guitar has had strings on it now for a couple of weeks, and it sounds pretty great. it's a 24.9 scale 000 guitar, but the soundhole and bracing is about 1/4" farther from the fingerboard than it should've been, due to an error ... matching the OM top's holes to the 000 body. I do wonder if it would've been a little more "open" sounding (or whatever) with the bridge a little farther from the center of the X, but I'll never know. The end result is still VERY pleasant, however.

_________________
"...you have to get over your strict adherence to your largely imagined notion of absolute perfection..."