LUTHERIE

Step 7: Assembling the Body

With the sides now bent, I was ready to assemble the body of my concert uke. I debated the relative merits of the different kinds of molds used to maintain the shape of the instrument during this process and settled on a compromise between the spanish-style workbord and a rigid mold. Makers of classical guitars and some steel string builders prefer the workboard, which consists of a guitar-shaped surface to which the bent sides are held in position by clamps. This allows the board to be used with any number of different sized instruments. The downside is that considerable attention must be paid to keeping the shape of the sides correct and symetrical.

The rigid mold consists of a thick series of boards with a cutout in the shape of each particular size of instrument that holds the sides in the proper alignment throughout the assembly process. This allows a very precise alignment, but requires a separate mold for each size or shape.

My "workmold" is a piece of MDF onto which I drew the ouitline of my uke. I then cut 1 1/2" blocks from pine and attached them at strategic points around the outline with drywall screws. Placing the bent sides into the mold (with the flat, "top" side down, I overlapped the untrimmed ends of the sides and marked the position of the mold centerline on each piece. I removed the sides and, using my mitre box and fret saw, I carefully sawed just outside the line on each piece, I touched up the cut, bringing it to the line with a sanding block. I then returned the sides to the mold.

This was a satisfying moment, for the uke was now visibly taking shape and my careful work had produced a near-perfect result. Enjoy such moments, because there will be times when your results will be less satisfying, believe me!

The head and tail blocks were contured to the curve of the sides on the belt sander and installed next. Before gluing, I drilled and countersunk the holes for the bolts which will attach the neck to the body. These allen head bolts, bought at Home Depot, will screw into threaded brass inserts sunk into the neck neel.

The mahogany kerfing strips were next. Taking a cue from the Martin factory, I went high-tech (for the 19th century, anyway) and held them in place with clothes pins while the glue did its work. The strips are slotted along their length to enable them to conform to the curved sides. I had to soak them in warm water for a few minutes to prevent the delicate strip from cracking when bent. I have seen cedar strips that did not require soaking, so use you judgement on this. I patted the strips dry and clamped them in place overnight. I removed them, spread a thin coat of TiteBond on the smooth side and re-clamped them.

These strips provide surface area for gluing on the back and top plates. My back is domed slightly, so it was necessary to sand the sides and kerfing to an angle matching that radius. I accomplished this by eye, using a sanding block. There are sanding forms for this purpose available from LMI and Stewart-MacDonald,

Using a cross-grained piece of 3/32" mahogany left over from the back plate, I made and installed the backgraft strip, which reinforces the joint between the two plate halves. This strip also allowed me to inlay a herringbone purfling strip along this seam without weaking the joint.

I then glued 1/4" x 1/4" bracing strips across the back, notching the backgraft where necessary. These braces were given a curved profile on the sander, creating a slightly domed shape to the back when glued fast to the plate. Thin strips of wood were placed around the edges of the back while the braces were clamped down, allowing the middle to sag to the required radius. This was all done very unscientifically - by eye mostly - but the results were quite acceptable (to me anyway!). I shaped the braces to a rounded profile with a sharp chisel and sand paper. The ends were ramped down to about 1/8". Notches were chisled into the kerfing so that the back would sit flat on the sides with the braces locked into place in the notches.

At this point, I made the decision to inlay a strip of herringbone purfling into the backplate. In fact, I had decided to embellish my uke more than originally planned. I would also add an inlayed herringbone rosette, tortoishell binding on the body, herringbone purfling around the perimeter of the soundboard and mother-of-pearl dots on the fingerboard. I decided that I would use my first instrument project to try out techniques that I would use later on other projects, figuring that this first attempt would no doubt be less-than-perfect anyway, so why not go for it? Had I planned to inlay a backstrip in the first place, I would have done so before bracing the back, but I just placed thin blocks under the edges for support and began.

The purfling is 1/8" wide, so I measured 1/16" on either side of the centerline and drew lines the length of the back. Using a straightedge' I scribed these lines with an Exacto knife to about 1/16" deep. I placed masking tape along the lines to prevent tearout and used a 1/8" chisel to excavate a shallow channel for the purfling. When the trough was a little over 1/16" deep, I test-fit the purfling and felt a satisfying "pop" as it snapped into place,

I glued the strip in and, after about two hours of drying time, I scraped the strip until it was nearly flush, finishing the job with 150 grit sandpaper.

It was then time to attach the back to the sides. There are many ways to do this but, because of the configurtation of my workmold, I went with a modified version of the "spool clamp." These are available from most lutherie supply houses, and are not that expensive at around $10 for six. I had a box of homemade clamps that I had put together years ago for laminating the mast for a wooden sailboat that I built. These were fashioned from 6" long, 1/4" bolts and pine 1x2's. I cut down the pine into 1 1/4" square blocks and presto - spool clamps! To protect the soft mahogany, I glued pads of cork to the underside of the pine blocks.

Had my board been cut down to a rough uke shape, I could have used the clamps as designed, but instead drilled holes all around the perimeter of the uke outline and inserted the bolts through from the bottom, placing the "spools", washers and wingnuts on the ends. I test-fit the back on the sides and tightend the clamps all around to check for gaps. I found that i needed to touch up both the angled face of the sides as well as deepening the notches for the braces in a couple of areas. This accomplished, I spread glue very carefully around the sides and clamped the back down all around. The sides, you'll remember had been arched, making the neck end about 1/2" shallower than the tail end. The back plate was thus forced to bend longitudinally to conform to this arch. Because of the dome built into the back when braced, this was a delicate procedure and required slow and careful tightening of the clamps, listening all the while for sounds of protest from the thin back plate. I was tempted to really tighten the clamps down to insure a tight fit all around, but I resisted, tightening only enough to make the joint close completely. I left the clamps on overnight, but you can be sure that I was back in the shop checking for signs of distress nearly every waking hour.

My fears were for nought, however, and when I released the clamps, I was rewarded with nary a groan from the tortured back. I was so excited that I neglected to take a picture of this stage of the project. I had recently bought a router base for my Dremel Mototool and I was itching to trim the overhang of the back plate flush with the body.

Using a flush-cut bit aligned with the edge guide of the tool, I hesitantly began trimming the excess wood away. It was easy! I soon had the overhang reduced to about 1/32" all around. I decided to touch this up with a "Robo Sander" drum chucked into my drill press. This sanding drum has a rubber wheel at its base which is the same diameter as the drum, preventing the drum from sanding too deeply. I smoothed the edge further by hand with 220 grit paper. Then result was far better than I had hoped, and my confidence was soaring.

There was still a long way to go at this point, but I was really starting to feel like a luthier!