[Originally Posted: Mar. 15, 2011]

 

In March of 2011, I built two more wooden sound boxes. The first is an 8" x 8" square box about 2¼" deep while the second "box" is an equilateral triangular shaped box with 11" sides and about 2¼" deep. Both boxes are built up from cherry trim wood that is sold in lengths of 2.2 m (220 cm) x 3 cm x 0.5 cm. After cutting the trim wood into eight 8" lengths, for each side I glued two 8" boards together side by side in order to build a box with a reasonable depth. Since the trim wood I used is 3 cm wide, the depth of my boxes are 6 cm, or about 2.25" deep.

 

Before gluing the wood together, be sure to view these two online videos by Kathy Matsushita, a fairly accomplished luthier: "The Easy Jointer" and "Joining the Top". These two videos describe the process for joining two pieces of wood to form the soundboard (or backboard) of a full sized guitar, but these methods are equally applicable to building deeper sides for a box guitar. The first video talks about a jointer, which I think is "over-kill" for box building, but it illustrates one way to make sure the two edges you will be joining fit together perfectly. What I did is used double sided tape to tape down a piece of sand paper to my work surface and then I would take the two pieces of trim wood I wanted to join, held them together and perpendicular to the sand paper and sanded then 10  or 12 times. Then, holding the pieces so the mating edges were together, and holding it toward a light source, I could easily see if the surfaces were mating perfectly or not. If not, more sanding.

 

In the second video, Kathy shows a fairly simple method of clamping two pieces of wood together using two lines of nails and a tent-like positioning technique. Just watch the video... it's easier to see and understand than to describe verbally. Also, instead of wax paper, I used strips of plastic I cut from old plastic grocery bags to keep from gluing my work piece to my work surface or clamp board.

 

[ Thank you for these 2 videos, Kathy. Very useful. ]

 

To cut the box joint "fingers & holes", you can use a table saw or perhaps a router. Procedures for doing it with electric tools can be found at other wood-working websites on the Internet. As I only have simple hand tools, I used a fine toothed hand saw, a chisel, a hammer, a small file and some sand paper to make the fingers & holes. The process I used was documented by Mag Ruffman at this link, but I will comment on my method as well.

 

To make box joints, first you must decide how many and how large the fingers and holes will be. If your side boards are an even number of units wide, then the size of the fingers and holes will often suggest itself. In my case, with sides of 6 cm, three fingers and three holds each 1 cm wide seemed natural, so that's what I used. On both ends of each side piece, I marked a line 0.5 cm in from the edge of the board. This is the thickness of the side pieces and would also be the length of the box joint fingers. Then, using a centimeter scale, I marked off where I'd make my cuts. I then would extend these lines around the board as accurately as I could. Here's how that might look:

Notice I also was careful to mark each "hole" I'd be cutting out with an "X" so I wouldn't get confused later on. Also notice that each end of the side board is notched in the opposite order. That is, one side will start with a "hole" and end with a "finger", while the other end will start with a finger and end with a hole. To make the cuts tighter, I doubled two side board together and cut the notches simultaneously. Once cut, I can flip one of the two boards over and have two sides which fit tightly when I assemble (glue up) the box.

 

I have some photos I can upload. Let me save what I have written, then upload the photos from my camera and then add them here...

 

Here are some of the tools I use for making box joints. Missing are a hammer, sand paper, and likely something else. But these should be enough to get you going. I recently replaced the 6mm chisel with a 10mm (1 cm) wide chisel, since most of my box joints will likely use 1cm wide fingers and holes.

Again, I can't overemphasize the importance of measuring and marking off the ends of your side boards to be cut. The following photo clearly shows how I do it:

The places marked with the X's will be chiseled out to become the holes that the fingers of the other piece will fit into as shown in this photo:

After all the sides are cut, you can dry fit the pieces together, trying to make sure each joint fits tightly enough to hold together pretty well in the glue-up process. If your joints are a bit loose, you can try taping them together as you glue them up using something like shipping tape. This will free your hands for doing other things like making sure the sides of the box are square.

Here, as you can see I have glued up the sides of the box and have clamped them together using what I call a tourniquet clamp made from a shoe lace and pen. I also used the square to make sure all my corners are square. After the sides have dried overnight, I filed and sanded down the finger nubs so the corners of the box was nice and smooth. I then cut out two 8" x 8" pieces of 2mm thick veneer to be used as the sound board and the back board. Next I glued on the back board. Once that dried, I found the box to be quite sturdy so I decided I would not need to add corner blocks to re-enforce the corners as I needed to do when I build my very first box that used butt joints. Next, I cut a slot to receive the neck in the middle of one of the sides of the box. Then I glued on a bit of wood to act as a kind of shelf to receive the end of the neck on the opposite side.

 

Here is a diagram of how the neck attaches to the box:

You can see the block of wood (what I called the "neck re-enforcement block") which is used to hold one of the screws that secures the neck to the box. The other screw is in the bottom of the neck where the neck meets the side wall. After bolting on the neck I cut and glued on the soundboard. After letting that dry, I finished off the instrument by adding tuners, a bolt for a nut, a bolt for a bridge and a home made wooden tail piece. The resulting instrument is shown below:

 

I am quite happy with the results. The instrument sounds really good and is quite loud, probably due in part to the 2mm thick veneer I used for the sound and back boards. When I tap on the back of the instrument, I can feel a puff of wind come out of the sound holes, something my earlier cigar box guitars don't really do. The instrument is strung up with strings 3, 4, and 5 from a set of six guitar strings and is tuned to D-A-D'.