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Week 9: May 7 - 20

Most of the work on this page was done May 7 and 8, as I got sick during the week and really couldn't do anything the following weekend. 

 

After the outline of the sides is marked on the back, the waste is trimmed to within a sixteenth of an inch of the line. The box is cleaned out and the box and back are set up for a last photo opportunity. I hope I haven't forgotten anything! You can see my signature and the date scrawled into the lower treble side of the soundboard. 

I bought some stuff at a surgical supply store that I thought would work in lieu of strips of inner tube, inner tubes being scarce these days of tubeless tires. It was a thin elastic material about six inches wide, intended for use in exercises for physical therapy. I cut a third off the roll, making it a two-inch strip, and tried wrapping the back down to the sides without glue and everything seemed quite alright. When I got the glue on, however, and started to wrap it again, the material kept breaking, to the point where I gave up on it with the glue sitting there drying. Plan B was nylon rope. I think this worked out well -- though as I write this the jury's still out, since the box is still tied up like this. Because the rope wouldn't cover every inch of the back the way an elastic material could, I added a couple of clamps just tight enough to bring the back edge into contact in the two places on the upper bout where it was a problem.

Well, it came out all right. There are no gaps visible between the back material and the side material. There was a small problem that I will describe later when a picture of it comes up. I used an edge-trimming bit in a laminate trimmer -- a tool that's halfway between a router and a Dremel moto-tool in size and kick -- to chew away the remaining overhang on the top. The back was trimmed closely enough before gluing. The next step is to install the end graft, a piece that joins the two ends of the side material as they meet at the bottom end of the guitar. The sides meet (theoretically) in the neck at the other end, so no treatment is needed there. First a pair of saw cuts are made and the side material chiseled away between them, right down to the bare wood of the tailblock.

The saw cuts are slightly further apart at the soundboard side than at the back side, so that a slightly wedge-shaped piece will fit in tightly, leaving no visible gaps. Sometimes this is done to the wedge-shape is obvious; I decided to make it only very slight. The end graft is a piece of cutoff from the back material. It is fit by taking a plane stroke or two on each side until it can slide all the way down into the slot, fitting snugly.

As you can see in this photo, there was a slight movement of the back while roping it down, putting the back center stripe between a thirty-second and a sixteenth off-center. Though it's obvious here, the back binding will come between the end graft and the stripe, so I hope it won't be noticeable. The two parts of the binding will meet here, so I'll try to make the meeting line up with the strip to further confound the eye.

Here's the scary setup I used to hold the box while doing this procedure. It's similar to the one in Cumpiano and Natelson. I'm going to think of something better. Actually, I saw a setup in The Big Red Book of American Lutherie, a collection of articles from the magazine of the Guild of American Luthiers, that I'll probably use.

Here's the end graft installed.

Here's my bench setup for routing the binding ledges. The guitar box is held between two bench dogs which are hidden under the plush towel that protects the box. Because the end hangs off the front of the bench, I've lightly clamped the upper bout. After routing up to the waist on both sides, I'll turn the box around and rout the upper bout.

This "design" for a binding-ledge routing setup comes roughly from the Donald Brosnac book that first inspired me with the notion of guitar building so long ago. I say roughly, because I didn't go back to the book to refresh my memory, but I must say I nearly memorized that book back in the late seventies. Forgive the multiple photos here; I didn't get one that seemed to explain the whole thing.

I used the basic Dremel router base as a starting point, removing the fence from its mounting as with the circle-cutting setup. I used the screws that hold the fence mount to the rail to attach a piece of 1/4" plywood to which was mounted the "finger" that will bear against the guitar side. By keeping the finger pointing perpendicular to the tangent to the curve of  the guitar's side at every point, a consistent depth of cut is maintained. This is easier than it sounds, especially if you slept through high-school geometry.    

I am using the LMI 1/8" down cut end mill. I originally tried this with a regular Dremel router bit, but the cut was very rough. The end mill was too long for the router base -- at the setting for the shortest cut possible, it stuck out more then the depth of the binding.  To solve this I added the 1/4" ply base plate to take up some of the slack. I used the screws that hold the Dremel base plate to the tool-holding mechanism or superstructure -- very convenient! I had to countersink the holes for the screws so they wouldn't ride on the guitar surface..

The end of the finger is based on a circle whose diameter is larger than the diameter of the bit. Therefore, if you point the finger a little bit off the perpendicular to the tangent, it cuts a little more shallowly rather than more deeply. This is good just for safety reasons but also because when the depth of cut is more than half the diameter of the cutter the wood can split away when cutting along the grain. I didn't know this ahead of time, but discovered it through experience. After that I began taking a first cut with the finger pointed 25% off to the side, then finishing with the finger perpendicular. I may get a bigger cutter.

Here's step one of the routing, the ledge for the binding strip. I'm going to put a small purfling band in as well, a piece of the black-white-black veneer strip. This will take another, shallower ledge which you'll see in the next photo. Here you can see the unrouted nib over the mortise. There's nothing for the finger to bear on there, so it will have to be taken down with a chisel.

Here you can see the second ledge and the nib left by that routing. To remove this nib I place the ruler along the cuts on either side and score the wood several times with a knife to establish the back edge, then clip it off with a chisel into the end grain. This bit is too small to use a chisel freehand with, as I did the first nib above.

Both the veneer strip and the binding strip are too brittle and stiff to simply glue on, so both are bent against the bending iron first. This proves difficult with the binding strip, because it is far from straight-grained. At one point I broke the strip clean through, with the grain running at 45 degrees across the strip. I found that using a block of wood against the back of the strip right at the point of bending helped to keep it from splitting.

I first glued the purfling to the guitar and then the binding strip to the purfled edge. I said that so I could use the word "purfled" and add it to my spelling checker dictionary. The strips are held down while the glue sets by pieces of masking tape. Some folks, I have heard, use cord or rope to do this. One amateur etymologist claimed in the MIMForum that this is why the binding is called binding. He's wrong. I think.* 

Here's what it looks like after gluing. The binding and purfling need to be scraped flush to the surfaces of the guitar. I've started that process in this photo, which accounts for the bits of fuzz you can see. I'm going to make a small scraper holder that can be held in one hand, because clamping the box down and contorting yourself to get the right angles on this while holding the scraper flexed with both hands is for the birds. Scraping it down is going to take a while, and I'd love to do it while sitting on the front porch instead of in my basement shop.

After a couple of pleasant hours with a scraper, the binding is level with the sides and back. At the top you can see the black-white-black veneer strips while the binding itself is rosewood with a strip of maple veneer at the bottom.

And now it looks like something.

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Copyright 2001 Stephen Miklos