MIMF

Does anyone know what the standard top radius of a 1940's Kalamazoo Army\Navy mandolin is?
I have one with a sinking top, so I'm taking the back off to rebrace it.

Anybody know? What's the most reliable way of measuring top radius? I really appreciate any help on this.

I don't know the top radius on your Army/Navy mandolin.

When I need to measure an unknown radius, I place a straight edge at the highest point of the arc, place a shim on the left and right, adding until it is straight across, touching all three points. Then measure the shims.

You can get you arch from those measurements. (I stick it into my CAD program if I am serious, or use 3 nails and a flexible stick for less serious work.)

You might inquire on the mandolin cafe site. Probably in the VINTAGE section of FORUMS. I have seen only a couple of these instruments in 30 years, and don't recall if there is indeed any radius. The idea was to make a cheap instrument to supply the military during war time at a time of materials shortages.

Steve Senseney wrote: When I need to measure an unknown radius, I place a straight edge at the highest point of the arc, place a shim on the left and right, adding until it is straight across, touching all three points. Then measure the shims.

Works great, but on a sinking top, all you'll get is the radius of the collapsing surface.

If the distortion in the top hasn't affected the neck angle, you should try Steve's technique, then add a random millimeter or two to the arch to bring the 'phantom' top back up to a proper height relative to the fingerboard.
Good luck.

Here is my guess, but I'm hoping that someone can maybe validate this.

The top definitely has a radius to it, I can see the arch at on the edges, but the rest of the top has sunken in. My (less than educated) guess is that these were built on the guitar line rather than the mandolin line. I'm wondering if they were built using the J-35/45/50 radius dishes. If so, did they use the back radius (which would make sense to me) or the flatter top radius?

I assume you have the bridge. If you project the string path to the bridge position you should get a good idea of how much the top has or has not collapsed by the difference in height of the bridge and strings. Remember you have to allow for the action of about .060" between the strings and the top of the 12th fret, or lay the straight edge on the frets and add 1/8" at the bridge for thew action. Otherwise you will make a radius to some as yet unknown spec and may have to reset the neck or make a shorter or taller bridge to accommodate. I would start with the bridge and existing neck angle and go from there.