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MAKING THE BACK

 

 I have a variety of Plexiglas templates which I use for laying out the back (and others for tops).  The Plexiglas makes it possible to lay out the back on the wood  for best effect.  I use a 1/8" Plexiglas for this. 

back-1-121.jpg (38428 bytes) Here I am laying out a piece of koa.  

 bkjg-45.jpg (24422 bytes)    After the back is sanded to thickness,  the shape laid out,  and fine sanded by hand, I glue the center seam strip in place.  Many years ago I made this clamp from some veneer press screws (available from many woodworking catalogs) and some scrap maple. I also use it to glue in the center decorative strip in the back.  

bkjg-46.jpg (25427 bytes) Here the jig is gluing in the back center reinforcing strip.

 

  This is the rough center strip in place after gluing.

 

wpe4.jpg (10336 bytes)    I then roughly shape the center strip with a skew chisel and then sand it to a smooth curved shape.

Recently I have modified my technique here.  I now preshape the edges of the center strip on my spindle shaper- I use a small roundover router bit, which cuts a smooth and consistent profile on the center strip.  It also leaves a larger portion of the strip flat which is useful since I have a new branding iron with my logo on it, which works best on a flat surface.  Even with this preshaped center reinforcing strip I carefully sand it before cutting grooves for the back braces.  

 

bakjg-47.jpg (27709 bytes)       The next step is to cut the grooves in the center strip for the back braces.   I use a jig made of machined aluminum..  It sits over the center strip and has carefully sized openings which guide the router --  which itself uses a template guide to follow the openings.  The cutter is set to just skim over the back, and thus remove the center strip.

bkjg-48.jpg (29599 bytes)  Another view of this jig.

bkjg-49.jpg (21973 bytes)  

back1-115.jpg (18796 bytes)   After cutting the grooves for the braces, I put my name on with a wood burning tool, and am ready to glue in the braces.

back1-116.jpg (19188 bytes)   Here I am burning the logo into the center strip.

 

back1-111.jpg (21615 bytes) This is the jig for gluing back braces - note the curved bottom piece, which matches the curvature of the brace.  

bkjg-50.jpg (30357 bytes) I have slightly rebuilt the brace gluing jig.  The clamping portion now has swivel feet on it and they are threaded into an accurately machined bar so that they are all in a straight line.  Works better than before, but not essentially different.   

back-1-076.jpg (43613 bytes)

 

wpe4.jpg (10472 bytes)   Gluing the braces on the back.  The clamps -- homemade-- have their bottom piece curved to match the curvature of the back braces.  These devices   are made of maple and the clamps are simply threaded rod and threaded inserts which are set into the top piece of the device.  The two white pieces are made of plastic and have grooves cut to the exact spacing and size of the braces.  These two "locators" in conjunction with the slot in the center seam strip insure that the braces are properly located and parallel.  This is important since I have a template for cutting the linings to accept the ends of the braces and this only works if the braces are exactly located.  This is all quite simple in execution and works well.

  A different view of the same.

 

 

    bkjg-51.jpg (28971 bytes)  And again.

 

wpe5.jpg (9216 bytes)    The back with all the braces glued in place.

 

 

 

This website and all of its content, text and images are copyright 1997-2011 by Charles A. Hoffman.  All rights reserved.

2219 East Franklin Ave.
Minneapolis, MN. 55404

hoffmanguitars@qwestoffice.net or choffman@hoffmanguitars.com

(612) 338-1079