Living Hinge Pineapple Ukulele

I made a pineapple ukulele entirely with a laser cutter, CNC router, and 3D printer. Almost no hand tools are needed for this project and it produces a great sounding soprano ukulele. All digital fabrication files needed to reproduce this project are included in the instructions. Have fun making!

The first step in the process is to cut the pieces for the ukulele out of 1/8" baltic birch plywood. I was able to arrange the shapes so they fit on two sheets of 12"x24" wood. To ensure the bridge would be placed in the right spot, I put some painters tape on the top face and cut out the bridge shape with a low power setting on the laser cutter. To ensure the piece was flat while cutting the living hinge, I placed hammers below the cut to press the wood against the base plate. The attached svg files were the documents used in the laser cutter.

The next step is to glue together the neck and the tail piece, making sure to keep the pieces aligned as they become slippery with glue between them. The neck shape was created by lining up the curved shape of the heal block and placing narrower pieces to create the rounded back. I used go bars, fiber glass rods bent between two surfaces, to clamp together the 1/8" pieces for the tail piece.

Once the neck and tail piece were together, I used go bars again to glue them onto the top plate. I then used regular clamps to glue the bottom plate to the base of the neck and tail piece.

Once the frame of the body was together, I glued on the living hinge sides. I've made a couple of versions, one with just lines in the living hinge, and one with holes at the edge of the lines to project the sound a little better. The body was designed to be circular so rubber bands could be used to clamp the sides on. I used some rubber bands across the top to hold down the sides against the curved part of the neck base, and a bunch of rubber bands around the curved part of the sides.

I used a CNC Router to cut the fret board out of 1/4" baltic birch plywood. The position of the fret slots were generated with an app I wrote in Easel, the software used to control Inventables X-carve machine. They were cut with a 1/8" ball end mill, with the frets further up the neck going deeper into the wood to allow them to sit lower down (this ensures that the string is free to vibrate when you press down on the fret). I then cut out the outline of the fret board with a 1/8" flat end mill. The image above shows me cutting three fret boards at once, but this link will take you to a shared Easel project with one fret board (workpieces are separated with the fret slots to be cut with the ball end mill and the outline to be cut with the flat end mill).

The next step is to glue on the fret board, which should line up exactly with the neck part of the top plate. The headstock piece should be glued on to leave a short gap between it and the fret board for the nut to be placed, lining up the holes for the tuning pegs. The bridge is made up of two layers, with the bottom layer leaving a gap in the back for the strings to wrap around the top layer.

I used 1/8" aluminum rod for the frets. I cut it to the proper length with pliers, then placed the pieces in the slots cut by the ball end mill, fitting neatly into the grooves of the same diameter. Once they are all placed in and pressed down, I ran some cyanoacrylate super glue into the seams above and below the fret. If the slots were cut properly, the frets should get lower into the neck as they go towards the body.

The next step is to 3D print the nut and saddle (piece that goes in the bridge). I used plain white PLA and set the infill to be 100%. This OnShape document shows the models that I used in the 3D printer.

The final step is to add the tuning pegs, and screws to guide the strings on the head piece. Because the tuning pegs are not angled down from the nut, the middle strings slip out of the slots, so I put a couple of screws in the middle of the headstock to pull down the middle strings and keep them in line with the slots. The strings are wrapped around the tie bar on the back of the bridge using this method, and guided through the slots in the saddle (3D printed part).