Bridgework

Looking back over the years I don’t know which is more sad, the regrets that mark your missed opportunities, or perhaps having no regrets at all. Having no regrets could mean that you never failed to kick the opportunity door open when it opened just a crack. More often it means that you just played a prevent defense, trying not to lose instead of going for the win.

One huge regret has haunted me for decades. As a young man I wanted to be a luthier, and I had one clear chance to do so, a chance I failed to meet. I had gone broke on my first spec house, sunk by an 18% building loan and 20% mortgage rates when we went to sell. I had nothing to show for a year’s work other than some bitter lessons learned, and was wandering the downtown wasting time and wondering what was next. I passed a shop that belonged to an instrument builder that I knew casually; I doubled back and went in.

I don’t remember his name now, but we struck up a conversation and he asked me what I was doing. Without thinking about it I replied that I was a builder (now busted flat which I didn’t mention) and he perked right up. “I’ve got a project that I just can’t get to, maybe you would take it on”. I had meant that I built houses…in the lutherie world a builder builds instruments. He ducked back in his shop and returned with a hand drawn pattern for the outline and dragon head scroll of a mandolin, and a nice slab of rosewood.

This door yawned wide open, I took the materials and told him I would get right on it. I was living in the upstairs of my friend’s house, no shop to speak of but I had built a work bench top for stained glass work. I dug out the luthier tools I had accumulated, sawed the rosewood slab to shape and started carving the arch of the back. This went well until the arched profile was done, and then I was stuck.

A better person would have crawled back to the shop, confessed the misunderstanding, and begged for the amount of mentorship I would need to finish the project. Blame the massive defeat I had just swallowed, blame a lack of character; I had to meet rent. I slid the project up on a shelf and looked for carpentry work.

That wood and the pattern has followed me from friend’s house to apartments to my first house to the house I have owned for twenty years and live in now. As I riffled through my small stash of rosewood looking for material for the bridge for my guitar I came across the cutout section from that mandolin back. Nice tight vertical grain, and bought so many decades ago it might even be Brazilian Rosewood… an excellent choice for a guitar bridge.

In a former life I would have tried to figure whose bandsaw I could use to resaw a bridge blank out of this substantial scrap. In my new incarnation I grabbed my Ryobi saw, clamped the scrap to my bench, and started milling. The offcut was a little over 3/4" thick, a 3/8" blank would do nicely, so I cut off one wing of the curved profile a little over an inch wide, scribed the piece up the middle of one edge, and carefully resawed it in half. Now I had two pieces just thick enough for bridge blanks.

What next? I had the outline of the bridge in my guitar plans and some architect’s velum paper, a little careful tracing and I had a pattern. I could have used my coping saw to cut the curves but I picked out a sharp chisel instead.

This is the good stuff, an antique chisel I had restored, re-handled, and honed, a finely grained piece of decade’s old rose wood, the occasional trip back to the strop to repolish the edge, this is the way I fell in love with wood carving in high school. When the outline was close I switched to a rasp like “razor file” from Stewmac Supplies.

In short order with a little finish filing and sanding the blank looked a lot like a guitar bridge, close enough that I used it to mark its future home on the guitar top for masking. Still though, I had a couple of tricky moves to complete.

The bridge glues to the guitar top, its function is to connect the strings and transmit their vibrations to that top. It has a narrow bone or plastic “saddle” installed in a angled grove as the last point of string contact before their barreled ends drop though the bridge pin holes to be secured by the bridge pins. The saddle is set at this angle to accommodate the differing amounts of force needed to push either thin treble strings or thicker bass strings down to the fretboard. More force equals more tension equals a higher pitch. The angle compensates for the differences and its geometry needs to be precise.

Setting this move up stopped me cold for a couple of days. Pro shops have “dedicated” aluminum jigs to make bridge milling quick and repeatable. They also use small electric routers. I wanted to do this with hand tools of course, and I was stuck until I viewed a Rex Krueger “Workbench Series” interview with master woodworker Garrett Hack about making and using “scratch stocks”.

The Gramil with the scraper end protruding down from the silver bar

A scratch stock is a cutting profile hand filed from a piece of thin carbon steel, like an old saw blade, set in a wooden handle with a slot to hold the cutter and a set screw to lock it in position. Its a very similar tool to the “gramil” I used to cut the binding channels on the guitar body. I had already ground a scraper end on the gramil blade and used it to scrape a narrow groove at the bottom of the channels. This scraper end was narrower than the saddle groove, but if I could make the right jig I could scrape a groove and then adjust the cutter over a skosh to widen it to the right dimension.

But how to set up the jig? Back to YouTube of course, and I found one luthier using 1/4" bolts, wide “fender washers”, and wing nuts to secure his bridge blank for routing. This was a great start, but then the question, how to set up a guide fence to direct my gramil cutter precisely along the angled groove I had laid out on the blank. I came up with this;

I have drilled a piece of 3/4" plywood for the 1/4" carriage bolts onto which the washers and wingnuts are threaded, then screwed that piece to a wider piece of plywood, wide enough to both clamp down to my bench and hold a tapered piece of pine up against the flat edge of the bridge blank. I have hand milled the pine to the thickness of the first piece of ply plus the thickness of the bridge blank and tapered it the desired angle of the saddle slot.

I then drilled two “stop holes” at the ends of the slot, (you can see one just above the silver rod that holds the cutter) honed up the scraper end of the blade, and carefully scraped my way down to depth, pulling thin curls of rosewood as I carved my way down. I carefully measured the protrusion of the cutter as I worked, ending with that protrusion at finish depth, then oh so carefully extending the cutter head to the full desired width of the groove and working down again.

I have marked the location for the bridge pin holes, as you can see in the title picture, and will drill them with the blank held in the jig before I file the same radius as is on the fret board onto the top of the bridge blank. After sanding the dome radius of the top onto the underside of the bridge it will be ready to glue to the guitar top, assuming I ever get the finish on that top right, which is another story;)

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John Griswold

John Griswold

Master carpenter, watercolor artist and beat up old jock…owned by Black Lab Bo who considers two tennis balls a minimum mouthful