On this first F5 I built I used the Siminoff method for the truss rod: Ace Hardware welding/drill rod with threads cut in, bent to an "L" at the body end and insert down into a hole in the neck base, drinking straw over the middle and a filler piece glued on top. On the peghead end I used a brass washer that I flattened on top. However--and here's the kicker--I used a plain ol' brass nut. I did NOT use a flared end nut. In all honesty I have never messed with the truss rod in the two years I've been using this mandolin, because by "using" I mean learning scales, chords, techniques (chop, etc.) and the absolute basics. I always has kept in tune fairly well and sounded--to my untrained ear--okay.
In preparing to radius the fingerboard I removed all of the frets, removed the strings and I put a straightedge on the fingerboard. With the strings removed I noticed a significant upward (i.e. toward the strings) bow on the fingerboard. The first two fret slots on either end are level but then beginning around the third or fourth fret slot at each end it starts to dip. There is a significant dip in the middle of the fingerboard.
I acquired an actual brass flared nut. I removed the old nut. (It actually spun freely, indicating it was never really tight to begin with...) I placed on the flared nut and began to tighten in order to pressure the neck in to flattening out the fingerboard. As SOON as it got some grip against the washer, as I tightened the neck would groan. I checked the fingerboard; exact same upward bow. I ignored the neck's squeaking/groaning noises and tightened again. Checked...still upward bow. I did this a couple more times every time with the same result until I just gave up and completely loosened the nut to relieve the pressure.
I'm not sure what to do now. The fingerboard itself is uniform in its thickness all the way around, so there is definitely a bow in the neck. But adjusting the truss rod nut seems to have absolutely no effect. How much can/should I tighten this thing? Or perhaps the way I set up the truss rod it simply doesn't work the way it should? Would appreciate everyone's thoughts.
Thanks.
-Mark
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