Fretting out on a fretless

One of my basses, an Ernie Ball Music Man Stingray 5, has [edit: what looked like] a problem with rising tongue, which is a kick up at the end of the fretboard, that can't be dealt with by setup alone. By way of measurement, if I have my strings set to say 6/64" at the 12th fret, the height at the end of the neck swings down to 5/64" as the fingerboard ramps up away from the neck joint. I don't know why this has happened, but it's probably been this way since the instrument entered my orbit 15 years ago. Prior to 2017, the action was unreasonably high, as the instrument needed a shim and I didn't know enough about guitar setup to know that's what I needed to put in there. Once the neck was shimmed properly and could be set to human-playable (read: sub 10/64") string heights, the buzz set in.

So, I've set to work on trying to solve this finally. First note: despite my optimism, ordering a 12" radius sanding block does not impact the reality that all modern Ernie Ball Music Man StingRay instruments have an 11" radius. The StingRay Classic and Old Smoothie instruments are 7.5", but no amount of optimism will make the 12" radius gauge match the fingerboard because it's not right. Once I had the 11" block on order from stewmac, it was time to tear the thing apart and set the neck to level to prep for sanding. An interesting question arises: how does one determine whether or not a neck is straight if you know part of the fingerboard is not? Normally, you'd use a straightedge down the whole length of the board, but if I do that, I either get backbow everywhere except fret 2 and 21, or I get too much relief the whole length of the neck. The solution is to use the slotted straightedge from Neck Check, as it's not long enough to touch both ends of the board simultaneously. You don't expect any curvature to happen on the heel, so you wouldn't normally need to check that part of the neck for truss-rod-correctable straightness.

Here's where I had a moment of inspiration.

Question: how do I then know, for sure, what I'm looking for?

Answer: if the neck is straight, and I line up a straight line feature of my house and look at it in reflection down the fingerboard, a straight neck will show me a straight line reflection fading out of focus the closer it got to me. A curved neck would, instead, show me a curved line and then no reflection.

Here's what I see when I look at mine, sort of kind of, as it's hard to line up a phone camera with the centerline of something and hold both still enough for pictures:

filename: "goobered fretboard.jpg"

So that little wink off to the left shows where I need to do my work here. The line is straight from the nut up to that point, and that point to the end is where the fretting-out buzz occurs. I'm excited, after all these years, to have a fretless bass that will play right. I had a fretless Jazz Bass I got in 2001 or 2002 that I took home with me on winter break once; I sold it in 2005 to fund the second in a series of bad decisions I was talked into by friends, and that is a disappointment I occasionally find myself feeling when I realize I'm missing out on a mystic ice blue or ice blue metallic Jazz Bass in my life, but I think having my StingRay in good, playable working order will more or less completely fix that. I'll still find myself wishing I had access to something in ice blue metallic, but I already find myself wishing I had instruments in nearly every color I've ever seen, so at least that wouldn't be anything new. Someday, they'll sell me a blue bass with a matching headstock... or a green Mustang bass with maple fingerboard.

Anyway, that's where I stand right now - I'm going to hit it with grits 220, 320, 400, and 800 and see what the finish looks like at that point, and if it's shiny enough, if the kink is gone. If it needs more, I have 1000, 1500, and 2000 ready to go. Update coming once the block is here and sanding starts!