CNC Uke

I thought about making a cigar box ukulele. The notion of re-using a cigar box, plus the overall funkiness of it appealed to me. But I found there is great demand for wooden cigar boxes and they don't come cheap. After agonizing a bit, I finally ordered a suitable one on EBay for $27. But I wanted to get started on the project and not wait until the cigar box arrived.

I thought about building my own cigar box. But that sort of took away from whole idea of reuse and funkiness. I looked online and found a 3d model of an entire uke one can 3d print in plastic. (see link below)

I didn't want a tiny plastic uke though, so I decided that I might as well try to make a "real" uke using part of the 3d print model for the overall shape.

I then found online a 3d model for a ukulele neck. It was for a "concert" uke, the next size up from the usual soprano ukes. The fret board seemed like a lot of work so I found one on Amazon and ordered two ready-made concert sized fretboards from China for less than $7 each. (see link below)

CNC machines are great. They make simple jobs out of what would be very difficult woodworking. I have a friend who prides himself on doing all his woodworking with hand tools, and he does a great job. In fact he was once an assistant to a luthier, maker of guitars and other stringed instruments. Well I'm not that guy. My woodworking projects are only acceptable if I can use power tools.

This Instructable is about building a "practice" uke while waiting for the cigar box to arrive. I've included pictures of the CAM screens in case anyone wants the details of how the pieces were cut out. The result turned out well enough to be played and looks like a real stringed instrument. I am quite proud of the fact that except for one piece of 1/4 inch walnut, all wood materials came from inventory, stuff I had in storage.

Links

Fretboard https://www.amazon.com/gp/product/B0171E9B5W

Nut https://www.amazon.com/gp/product/B07MJBF322

Tuners https://www.amazon.com/gp/product/B003QFA808

Bridge https://www.amazon.com/gp/product/B0116TFMM4

Replacement Strings https://www.amazon.com/gp/product/B07N26D2T8

Source for uke hourglass shape https://www.thingiverse.com/thing:804817

3D Model for neck https://forum.vectric.com/viewtopic.php?t=25486

Dimensions

Uke Shape was 279mm x 244mm

Sound hole was 52.4mm

Hole Trim was 60mm outside diameter

I found online the dimensions for a concert uke and re-scaled the uke-top model so it would have the recommended size for a concert uke. This hourglass shape formed the basis for three different CNC cuts, the frame, the flat bottom and top, and the bead trim.

The Body Frame

I used 1/2 inch plywood for the top and bottom frame pieces. I copied the shape vector to make a to make an inside vector for the profile cut. As the picture shows, the distance between outside and inside vectors is not uniform. I learned later how to use the Offset Selected Vectors function to create a uniform inside vector.

The Body Sides

I used 1/8 inch Baltic Birch plywood for the curvy sides. I used a piece about 5 feet long and ripped it on the table saw to 2 1/4 inches wide. I verified that the length was sufficient with a similar length of very limp plastic, bending it around the frame. To allow the plywood to bend I used the table saw with cross-cut sled to make shallow cuts, many many shallow cuts on one side. This cut away all but one thin layer. The result was quite flexible and bendy.

The Top

I used more 1/8 inch Baltic Birch plywood and used the CNC machine to cut out the shapes for top and bottom. The top and bottom were the exact size of the outside of the frame. This would leave the edge of the sides showing. It needed trim pieces.

The Trim/Beading

For this I used 1/4 inch walnut. Full-sized pieces of walnut were not available so I used the CNC machine to cut 4 half pieces. In setting this up in my CAM program, I used the Offset Selected Vectors function to create the inside vector for profile cutting.

The Sound Hole

The sound hole needed some trim too. I used the CNC machine to cut a trim piece out of 1/4 inch walnut in two steps. The first, a pocketing step reduced from 6mm to 3mm for the portion to be on top. The second step cut out the profile, leaving a small lip to fit inside the sound hole. I sanded the outside corner of this to match the body trim.

The Curvy Sides

Top and bottom frames stacked together provided a better clamping surface for my bendy plywood sides. The plan was to glue the sides only to the bottom frame, then separate the frames after the bottom's glue dried. I thought if the top accidentally got glued in place while stacked on the bottom, I'd cut another frame for the top. Fortunately this was not necessary.

My first attempt to clamp the side to the frame was met with a sharp snap. Dang. So I went back to the table saw and for the second time made many many cuts. This time before clamping to the frame, I sprayed the side with water, and blasted it with the hot air gun. Success.

I let the water dry and glued the bottom frame to the sides, holding the clamped assembly upside down and dribbling a little glue between sides and bottom frame. After the glue was dry and the clamps were off, I was pleased and relieved to find that the top frame pried neatly away from the bottom and slid into place at the top. I glued and clamped that in place, and added more glue to the bottom also.

The Top

I glued the top in place against the frame but left the bottom to be attached later with
screws. For the trim, I glued the halves into place on top and bottom. After the glue was dry I did a lot of sanding to round over the outside edges of the trim.

The Bottom
The bottom trim was already in place, so the bottom required some sanding to make it fit within the trim. I attached the bottom to the frame with 6 small flat head wood screws. I wanted the bottom to be removable in case the neck needed to be removed to adjustment or if I wanted to add some electronics inside the body.

I sprayed several coats of matte finish on the body - sides, top and bottom.

I found a model for the uke neck on the Vectric (CAM program) forum. (see link in Overview Step). I had a 2 inch thick piece of basswood "in inventory" so I used that. The model assumes a thicker piece and has a longer section that attaches to the uke body. I rarely do this, but I edited the G-code to skip the part where it would be carving non-existent wood. I used a hand saw (Japanese pull style) to cut the bottom. It came out rather well.

The only surprise came later when I started to install the tuning pegs. I had hand sawed the tuning head portion at a slant because I thought it looked cool. But the thicker part prevented the tuning pegs from poking through. Oops. This time I used a plane and sander to remove the slant. I was impressed and pleased that the fretboard and neck matched so well. I glued them together, filled in some voids with wood filler, then did minor sanding. I glued the "nut" in place at the end of the fretboard. I sprayed several coats of gloss finish on the neck, masking the fretboard.

To provide more strength where the neck would be mounted, I glued a piece ot 1/4 inch plywood scrap inside the body. I used two screws to attach the neck to the body. Now it started to look like a real uke.

I had bought a pre-made bridge at the same time I bought the fretboard. Typically the bridge is glued on to the uke top. Per instructions gleaned from the internet, I marked the location for the bridge and masked carefully around it. I sanded away the finish down to bare wood so the glue would adhere well. I glued and clamped it in place. All the glue I used in this project was yellow carpenter's glue. I was told later that the real luthiers use hide glue. I guess this allows a joint to the undone by heating.

Finishing Up

Mounting the tuning pegs was straightforward (since the head was now sufficiently flat). I installed the strings, hoping that the bridge wouldn't pop off (I gave the glue a full day to do its magic). And it's done!