It Worked for Me: Fretboard Radiusing Jig

by James Blilie

Originally published in American Lutherie #132, 2017



I have always found creating the fretboard radius a laborious process. I never liked sanding it all the way using a radiused sanding block: too slow, too much work. I wanted a way to get it close enough so that the final sanding with the radius block and the 180-grit sandpaper would complete the job quickly and without so much effort. I’ve seen several luthiers use a shaper to put the basic radius on. (I don’t have a shaper.) I used to sometimes use a plane to rough out the radius before sanding, but this method was laborious and hard to control.

Dissatisfied with my previous methods, I designed and built a jig that bolts onto my 6˝×48˝ flatbed belt sander and provides the radius for the fretboard. The inner frame holds the fretboard using double-stick cloth carpet tape. This sits inside of and is bolted to an outer frame that clamps to the sander, using locating pins. (I drilled holes in the sander frame and put the pins into the wooden jig frame.) The interface between the inner frame and the outer frame is a radius. Both sides of the interface are cut from a single piece of 3/4˝ Baltic hardwood plywood (well, two pieces, one for each end; I screwed them together for cutting the radius). Take great care cutting the radius as this single bandsaw cut defines the interface. This radius is not the desired radius of your fretboard: It is the desired fretboard radius minus the distance from the interface to the sanding bed. This radius must be calculated as part of the design of the jig.