Brazilian rosewood, for a 1949 0-18
Making a Martin Bridge
© Frank Ford, 6/12/00; Photos by FF, 0/00

This bridge needed to be replaced because it had been cut drastically low in an effort to avoid resetting the neck. Then, years later, the neck had pulled up more, making the reset a necessity. It would be a shame to reset the neck to suit this low bridge, so I'm replacing it with a new one of the original height.

	This is the L.M.I. heat blanket, wrapped in aluminum foil. It reaches about 400 degrees Fahrenheit, and I keep it on the bridge for about ten minutes to weaken the glue joint.
	A rounded flexible putty knife is just the thing for lifting the bridge.
	As you can see, it came off with little damage to the spruce top. Looking at the back edge, you can see the darker area where the bridge had been slightly loose for years.
	In 1949, Martin made their bridges with the pin holes forward about 1/16" from their location on more modern instruments. So, it wasn't a matter of question. I had to make the new bridge rather than obtain a replacement from the factory. To get the hole locations and outline transferred perfectly, I simply stuck the bridge to a piece of wide masking tape.
	Then, cutting around the bridge, I got the outline just right.
	Punching through the holes
	and trimming the tape, I had them perfectly located on my template.
	All I had to do was stick the tape to the bottom of my bridge blank.
	Let me back up just a bit. Here's the bridge blank I had made up in advance.
	As you can see, the "wings" are formed by simple radius cuts. The radius is 1.0", and they are always the same distance apart, so it's reasonable to make up blanks ahead of time. That's a standard new Martin replacement bridge I'm holding in front.
	My first step is to flatten and straighten the front edge, and I find it easy to do with some 150 grit sandpaper on a flat plate.
	Next, I'll drill the holes with a 1/16" drill bit. I recently discovered these Black & Decker "Bullet Drills" which have a point cut similarly to a brad point drill. They cut like the devil, and really cleanly. Best of all, they're in stock at my local hardware store.
	I always drill a new bridge to 3/16," the smallest hole a string ball fits through with ease. I'll be increasing the diameter once I ream the holes for the bridge pins after gluing the bridge in place.
	Because I'm drilling from the bottom, and the blank is quite a bit over final thickness, I don't have to worry about chipping. Nonetheless, these drills leave a clean exit wound.
	I use my little 1x42" belt sander for just about everything. In this case, for taking the bridge right down to the edge of my masking tape template. I'll sand the edges more smoothly by hand later.
	Laid in place, I can mark the ideal finished height of my new bridge by projecting the top level of the frets using a straightedge. I want my new bridge to be just at the height of the straightedge laid on top of the frets.
	Now I have a nice line to follow.
	back to the little sander, with its 60 grit belt. It takes almost no time to hog off the excess material on top.
	There, you can see the result. It has 60 grit cross grain sanding scratches, but otherwise pretty neat.
	Working freehand on the flexible portion of the belt above the platen, I begin rolling off the back contour. I'm mostly just removing a bunch of stock here, and will true up the shape by hand sanding.
	Here its, roughed out.
	Clamped in my Versa Vise, the bridge gets a bit of cleanup with a double cut file. I'm removing the heavy sanding scratches and evening out the top radius.
	Same for the back contour. I could actually produce the entire shape by hand filing, but the little belt sander is much faster.
	Now, I'm block sanding, starting with 150 grit, finishing up with 320.
	The front edge has a bit of a radius, and I produce that with my sanding block.
	Block sanding the bridge tips, I make sure to keep everything level and flat.
	A quick trip to the buffing wheel (this one has black compound, so it doesn't pack the pores with white stuff) to give the bridge a shine.
	It's not my final finish, but just a handy way to reveal any leftover sanding or filing scratches. My final finish will be with 320 grit and #0000 steel wool.
	All through the carving process, I'm super careful not to round over the sharp edge that defines the top area of the bridge. Martin bridges always have a very crisp line here, and it's always straight and perpendicular. I don't want my new bridge to look like anything but a stock Martin original.
	My heavy duty scraper started life as an old kitchen knife. It's necessary to scrape the old glue off, and just a tiny bit of the spruce as well. In order to get good adhesion with hide glue, I need to remove the oxidized surface of the wood.
	Same with the bridge. Glue sticks best to freshly prepared surfaces.
	About ten seconds in the microwave heats the bridge to about 120 degrees, giving me a bit of extra time to get my clamps placed and tight.
	Now that the bridge is glued in place, I can plot the ideal location of the saddle.
	Here's a very important piece of trivia. Martin bridges with "through-cut" saddles have the saddle slot higher on the bass than the treble. That way, the bridge, which is a bit thicker on the bass, will have about the same amount of saddle "revealed" at each end of the slot. I set my caliper at zero on the treble, moved to the bass, and found that the bottom of the slot was just about .050" higher at that end. That's the way they have always been, by the way.
	I mill the saddle slot with my bridge router mill, which cuts a very neat slot indeed.
	I have the bass side of the router mill blocked up 1/8" so that my slot has the same slope as the original.
	I don't know if you can see it, but the saddle slot looks just like the original.
	A quick pass with the 3/16" bit to clear out residual glue.
	This is the one-flute reamer available from L.M.I. It clogs like crazy, but that doesn't seem to impair its function.
	I like it because it chucks right into the old Makita, and zips the holes to the right taper and diameter. I check the depth with the bridge pins as I go.
	I have a little multi-flute countersunk permanently chucked into this old cheap hand drill. That way it's always handy for a quick bridge job. In making Martin bridge replacements, it's important to take note of how much the tops of the holes are beveled. Martin uses a fairly light countersink.
	A few strokes with the bridge pin hole slotting saw, and I have clearance for the strings.
	Here's a cool little tool for holding a saddle while you're flattening it with sandpaper on a flat surface. It's nothing more than a piece of acrylic with a recess cut to hold the saddle captive. The saddle rattles around a bit, but that doesn't interfere with the sanding process.
	My blank trued up and sanded to thickness, I place it in the slot and use my half pencil to mark the ends precisely.
	After roughing the ends on the little belt sander, I hand sand them to fit using an acrylic tube (2" diameter to match the bridge tips).
	#0000 steel wool gives just the right finish, followed by a light application of mineral oil to bring out the color of the rosewood.
	All done, and looking good. Aside from the fact that it looks new and clean, this bridge could pass for an original.

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