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Greetings...
Having some oddball numbers on a top. Usually both sides are somewhat close when doing deflection tests.
In this case, the numbers I'm getting are very spread apart, one side up is much more flexible than the other.
I accidentally got a top flexing .270, 5lb at 18".
It's for an OM. I usually shoot for about .225 on an OM. Anybody have any thoughts?

I think it would be really hard to answer this as there's a lot unknowns. Is this one half of the top or joined together? Is there a soundhole in it already? Whats the load footprint look like, a line across the top or a 5lb can of beans? etc..
Of course I can't really answer, but I'd guess it's light in weight and you should be able to make up for it in your bracing, or set it aside for a parlor.
It'll be interesting to see what others have to say.

_________________
Jim Watts
http://jameswattsguitars.com

Just don't look at the numbers and everything will be fine Let your fingers guide you.

If you want to build a guitar that sounds like others you've done with a .225" deflecting top, then pack that one away for later or send it to me. But I'm sure it's still usable if you want to be adventurous. I've never tried measuring deflection numerically so I'm not sure how floppy .270" would feel, but it sounds pretty stiff to me (what's the species and thickness, to get the general idea?). If it's really floppy, use a large "Somogyi style" bridge plate, or a bracing pattern that supports against bubbling behind the bridge. Lately I've been using 3 or 5 fan braces in the lower quadrant.

I use 5lb at 18" too and .270 is a bit more than I like for an OM. I'm at around .260 for a size O.

How thick is it? I'm certainly no expert but I would probably use it if it wasn't too thin. Maybe brace it a little stronger and backoff on the usual thinning around the rim.

_________________
Steve Smith
"Music is what feelings sound like"

Thanks...
It's lutz, coming in around .105ish.
But according to the principles of deflection testing, shouldn't both of those tidbits be irrelevant?
However, I think the major problem was inaccurate measurement. The top was not completely flat so I I was getting wildly different measurements on each side.
So, I took a straightedge across the beams and used that to calibrate my zero point, and the numbers I got made a lot more sense a was in the range I was after.
May be the way to go....

You can preload the top with a little weight, then zero your indicator and then add the 5 lbs. You should get better measurements that way with a top that's not flat.

_________________
Jim Watts
http://jameswattsguitars.com