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Fender Neck Shim, Bolt on Neck Reset



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1. A Fender Jaguar.  This is a newer black top model that could use a set up. 2. High Action.  At the 12th fret, the action is about 3.15mm as measured to the top of the string.  I’ll take a look at the bridge to see if I can lower the action there.
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3. The Tunomatic style bridge is already as low as it can go.  In order to lower the action, I’m going to have to adjust the neck angle.  I’ll do this by making a wooden shim that will fit into the neck pocket of the body.  First, I’ll take some measurements to plug into my fender neck reset formula. 4. Wiggle Room.  I’ve adjusted the bridge to my desired bridge height; a couple of millimeters above the top of the guitar.  The formula is (XZ)/W.  A big thank you to Stu Berg for sharing his formulas with the guitar repair world.  I could just insert a guitar pick or similar into the body end of the neck pocket and do some trial and error until the action is lower but that’s time consuming and leaves minimal contact between the neck pocket and neck heel that can lead to warping at the end of the neck and a decrease in sustain.
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5. Z = 2.84.  With the bridge adjusted to my desired height the action is 4.17mm measured at the top of the string at the 12th fret.  My target action is 2.75mm, a difference of 1.42 mm.  I multiply the desired change in action by 2 to reach Z = 2.84mm, the distance that the neck has pulled forward as measured at the bridge. 6. W = 235.  The distance from the neck/body joint (located just before the 17th fret) to the 6th string saddle is 235mm.
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7. X = 76.  The length of the mortise (or neck pocket) is 76mm.  (76×2.84)/235=.918468mm which is .036″.  Because it’s fairly time consuming to hand-plane a shim thinner than .010″ my shim will taper from .010″ thick to .046″ thick, a change in thickness of .036″. 8. Tracing the Footprint of the neck heel onto some 1/8″ thick mahogany.  I’m using mahogany because it’s easy to hand plane, although just about any hardwood would work.
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9. Bandsawing the shim to the pencil line. 10. Hand-Planing the shim on my bench-hook shooting-board to it’s final width.  I’ll shape the end-grain of the shim to its final fit with the disc-sander.
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11. Tapering the Shim.  I hand-plane across the grain with the Veritas skewed block pane against a block of maple in my end-vise.  I check my work frequently with calipers until I’ve reached my final taper. 12. Drilling Holes in the shim for the screws on the drill press with a brad point bit is fairly quick.  I use a reamer to enlarge the holes.  A little piece of the shim broke off during the drilling process which wouldn’t have happened if I had remembered to drill the holes prior to tapering the shim.
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13. Dyed Black, the shim is tough to spot.  I only dyed the exposed edges of the shim. 14. X-Low Action.  The top of the 6th string is about 2.75mm from the top of the 12th fret.  The bridge is right where I left it, about 2mm above “the deck”.