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Another take on a radius device

Discussion in 'Luthier's Corner' started by Hambone, Jan 20, 2005.

  1. Awhile back I mentioned in a thread that I had come up with an idea for a radiusing machine that had the router in a stationary plane and the fretboard blank moved. Well, I finally got the drawings somewhat legible and I thought I'd throw it out for discussion.

    After this weekend, I'm even more convinced that this approach is a better way than the rockin' rail system we've all been using. My reasoning is that neither the fretboard blank or the rails and sliding arches are perfect in shape. These small imperfections in the mating surfaces manifest themselves as marks on the fretboard during shaping. That's what happened to me this weekend. I found that as I moved my router down the rails that the rises and falls in the fretboard were accentuated when they were paired against a similar imperfection on the rails at the same point. It occured to me that if I were to use a system where only the blank or the router moved laterally, I would eliminate half of the error and make less work sanding when it was done. I sort of experimented with this idea on my rail system and it worked. I will now use a set of stops on my rail system to trap the router base at set point on the rails - it won't move laterally, just back & forth. The blank is then pushed under the bit to radius the top.

    This device was concieved before I even saw JP's jig. The simplicity of that design prompted me to build that one as my first attempt to make something to help with radiuising. I may still build this macine to make the task of doing different radii without having to use different sled traks. That alone would make it worthwhile to attempt.

    The design is essentially plywood and aluminum. The main struts are 1" x 2" aluminum channel. The pivot points of the various radii are located on the side plates and the axle itself is moved to a different set of holes to change the radius. This keeps the router platform at a constant height and distance from the platform supporting the fretboard blank. I didn't illustrate the router motor installed for clarity.

    For your approval:
  2. schuyler


    Aug 5, 2003
    Atlanta, GA
    i like the idea... here're some questions:

    can you do compound radii boards by setting each end of the jig?

    what's your estimate for the setup time for each blank?

    i do my radiusing by hand, which is about 10 minutes a board. i'm curious if this will be faster, given that you'll still need to sand the board lightly?
  3. budman

    budman Commercial User

    Oct 7, 2004
    Houston, TX
    Formerly the owner/builder of LeCompte Electric Bass
    Looks like a neat idea, Hambone. Sort of a reverse pendulem. Would the sliding surface utilize some sort of bearings for ease of movement? I wouldn't want something to bind in the middle of a cut.
  4. Sounds like your doing yours on a belt sander with the pendulum method. This device won't compete with that and is more for the guy that doesn't have the 36" belt sander required for compounding.

    The alignment of the parts won't allow two different radii.

    Setup time should be about 2 minutes. Just move the pivot axle to the proper pair of holes.

    I think that any method using a router will require some sanding. This design was conceived to cut that amount in half over the other method
  5. You wouldn't need anything more than to surface them with some high pressure laminate. That's slicker'n greased owl manure! ;)