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*Metric* radiused sanding blocks

Discussion in 'Hardware, Setup & Repair [BG]' started by Ian Perge, Sep 25, 2004.

  1. Ian Perge

    Ian Perge Supporting Member

    May 11, 2001
    Evansville, Indiana
    After consulting with the two luthiers in the nearby area (the first of which "defrets" by grinding down the fret to the tang, the second who refuses to do defrets at all, citing "it weakens the neck" :rollno: ) I've decided to take the plunge and do it myself. I've researched various methods online by both amateurs and professional websites, traded e-mails with a friend's bassist who's done the same, and I'm confident I can do a more-than-adequate job given the proper tools which I'm prepared to spend the money on.

    ...until one problem reared it's ugly head. I'd like to use a radiused sanding block to make sure I don't leave any humps or flat spots after trimming down the inlaid lines, but the bass (a Yamaha RBX 775) is far-east made, and therefore has a radius measured in millimeters and not inches due to that newfangled metric system. ;) I've tried searching online, but cannot find any radiused sanding blocks like the ones Stewart-MacDonald carries but metric. I'm looking for a 600 mm radius, which coverts to 23.6/23 & 5/8ths.

    Does anyone have any suggestions as to a fairly cheap and easy solution to this problem? I have friends overseas looking, but they've had no luck as well in finding anything. Hell, if anyone reading this has the capability of fabricating one, I'd be willing to pay a fair fee (akin to StewMac's product plus a little "thank you") and shipping.

    Thanks in advance for whatever advice you can provide. :)
  2. Howdy and welcome to Luthiery!

    I think you're over thinking this a bit. Having radiused fingerboards (my own constructons and others), I've found that there can be a relatively large amount of error in the radius measurement before you can notice it in the feel of the neck. At least that would be true of most all players but the top virtuoso's. Here's how to prove it - Draw an arc with a 12" radius. Then draw another arc centered (tangential) inside the first one that is 11". Measured at 2.5" (widest part of neck) this would only equate to a drop of .006" on each side. Of course there is a large variation in the actual diameters of the two circles but when the two radii are compared in this orientation, there is very little difference to be felt. The difference between the metric and US measurements would be even smaller since the difference. 600mm is 23.622" but the difference between that and a 24" radius on a 3" wide fretboard is less than .0001" of each side. This is way beyond our human ability to sense by feel. BTW, I used 3" in the second example because I had to go up in width to get any measurable difference at all using my method of calculation.

    Also, for what it's worth, that is a pretty flat neck to begin with. The difference between your neck and flat is .047". Also remember that these examples are at the widest part of the neck. The variations will decrease as the neck narrows towards the headstock

    I've made my own radius calls and I've even designed and made my own adjustable radius sanding block. It works well and was easy to make.

    Hope this helps
  3. Ian Perge

    Ian Perge Supporting Member

    May 11, 2001
    Evansville, Indiana

    Thanks for the response and very detailed explanation. Logically I knew that the difference was minimal at best, but with the method in which you broke down just how minimal the change in radii would be, it *clicked*. I know feel much more comfortable in using a 20" as a substitute and with as little usage as possible (i.e. trimming the inlays and hand-sanding as much as possible)

    I've also received work from a name people would know about making the lines a bit more eye-catching that the usual inlayed wood strips. I don't want to jinx it by saying any more, but if this works out I'll be one happy camper. :D

    Once again, thanks.
  4. Tim__x


    Aug 13, 2002
    Alberta, Canada
    Ooh, intruiging. Mind if I take a guess? Plexi-glass and fiber optics, for glowing fret-lines.
  5. Ian Perge

    Ian Perge Supporting Member

    May 11, 2001
    Evansville, Indiana
    Yes, because I just discovered a fully equipped workshop and several thousand dollars underneath my place. ;)

    Not quite at that level, but a bit beyond your standard ghostlines. If it works out I'll be sure and post pictures. Hell, if it doesn't and I have to make due with more typical lines I'll post pics, because I'll have done it myself without ruining a neck. :)