Sunday, November 8, 2015

Making a pyramid bridge

  So, you want to make a pyramid bridge?  Or perhaps you already make them and just want to see how I do it.  Or maybe you don't want to make bridges or guitars at all, but just enjoy looking at photos of the process.  Well come one and all and have a look.

  There are a few common variations on the venerable pyramid bridge.  The profile I like the best can be found on a variety of old makes of guitars and has a deep curve that swoops up the side of the pyramid.  Here's an example of a bridge with that sort of profile that I pulled off a no-name parlor guitar some years ago.

  I just love the shape of this bridge.  It has tight scoops between the pyramids and the center, and the angles are steep.  The peaks of the pyramids are as tall as the center of the bridge.  It was made in Germany and still bears the old stamp to prove it, as well as some barely visible file marks here and there.  The guitar it came off was made in an American factory, but often parts like bridges, and pre-cut inlay were supplied by specialty vendors.  Unfortunately this bridge broke long ago, but I carved a matching replacement for the guitar it came off, and I've kept this one around as a visual inspiration for future projects.  The pyramid bridges I make have a few differences in design, but I try to keep the overall feel the same.

  Like most lutherie projects, you start off with some nice wood.  In this particular case I'm using an old piece of Honduran Rosewood, but I've also used Ebony, Maple, Walnut, Pear, Locust and more.  This piece of Rosewood came from Oby Johnson at Targo Woods in Bellingham.  He shipped a bunch of wood back from Honduras in the early eighties and still has various chunks of it scattered around his shop (a must visit place for any wood folks in the NW).  This is what I started with...

   It doesn't look too amazing til you cut into it and then...

  I cut out a blank on the bandsaw approximately 1 1/8" by 6" by 3/8", then I quickly true the edges on the belt sander.

 Next I carefully layout the holes for the bridge pins, and drill them out with a 3/16" bit.

  Then I just screw the blank down onto my "bridge carving jig" which is just a piece of scrap wood that I clamp into a vice.  The screws just go through the bridge pin holes.  This allows me to easily access all sides of the bridge for carving.  First step in the carving is cutting out the scoops.  I do this with a coarse half round rasp and it goes very quickly.

Then using the flat side of the rasp, I start cutting the pyramids one face at a time.

  Here's a view from the side.  The rasp leaves deep gouges and I'm careful to not go too close to the bottom edge.

  At this point both pyramids have been rough shaped with the rasp.  It takes some care to keep things centered and even.  I don't use any layout marks, I just rely on my eye to say when things look right.  Next I'll clean up the rasp marks and refine the shape with a file.

  I'll unscrew the bridge from the platform now and work on the shape of the center.  Here I depart a bit from the design of the old German bridge.  I like the bridge pin side of the bridge to taper back from the saddle side.  I also give the top of the bridge a slight curve to correspond with the radius of the fretboard.  I quickly create the rough shape with the help of the belt sander.

  To create the slot for the saddle I use my "bridge slotting jig".  As you can see the jig is made of scrap wood and I change and adapt it as necessary.  I mark the line I want on the bridge, set it in the jig using the router as my reference, screw it down, and rout away.

  The saddle slot is set at an angle, or compensated, for ideal intonation.  A lot of my favorite old guitars have saddle slots that go straight through the sides of the middle part of the bridge (like on the old German bridge pictured above).  It's a great look, and I'm always tempted to do it to give my guitars that old style authentic touch, but it's more likely to split over time, so I stop the slot just before it goes through the ends.

  My flat top guitars actually have a very slight arch to the top.  This is pretty common, to put a very small curve into the braces before gluing them to the top, then the top is flexed to create a slight dome.  I shape the bottom of my bridges to fit that dome on a slightly convex sanding block.

  Finally I'll finish sand the entire bridge,  give it a quick french polish and...  voila!

  There are certainly other ways to make a bridge from bandsaw jigs, to all on the belt sander, to CNC machines.  This way done mostly by hand works great for me and after making a few of them it goes pretty quick.  They are not 100% perfectly symmetrical, and there may be a tiny file mark left on an edge, but to me that is part of the beauty.  I love seeing a file mark on an old instrument.  It's usually something I'll only notice after close examination, and then my imagination gives me a glimpse of some long gone worker in a shop, using their hands.