Banjo Ukulele (Banjolele)
by AndreasBastian, published
I've included old versions of the body for anybody who is curious. They have different bridge support structures (rev1), webbing designs (rev2 & rev3), and membrane thicknesses (rev4) that all impact the tone significantly. I designed the instrument to allow the head portion to be swappable to allow for easy exploration of head design.
Finally, be sure to check out the spectrograms comparing open string plucks of the printed instrument and of a classic ukulele. More on that [here](http://andreasbastian.tumblr.com/post/55515120007/i-spent-a-few-nights-and-weekends-this-june).
[See the video on Vimeo!](https://vimeo.com/70293194) [And on Youtube!]( youtu.be/hS0AWEd63kU)
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Great analysis locofocos! I pulled all the measurements for the neck directly from an old banjo-uke, so I'm not sure what acoustics design rules apply to those vs. traditional ukuleles. There is definitely room for improvement of tuning using mathematically-grounded geometries. I do know from experience with this particular instrument that the bridge position and angle, as you pointed out, are quite important to tone volume and quality. And as for modifying this design, go for it! I specifically designed it to be modular so that the resonating body could be easily swapped out. Like-wise with the neck.
Just found out my school has a free to use 3D printer, and would love to try this! I'm an avid guitar and ukulele player. I've also read about minor adjustments of fine details like the bridge placement. As I understand, the 12th fret needs to be exactly half-way between either ends of the string (from the nut to the bridge, then give yourself a little wiggle room to finely adjust the intonation). Just measuring it on the main image, it looks like you've got about 288 pixels from the nut to the 12th fret, then 223 pixels from the 12th fret to the bridge. That's about 77% as far as it needs to be. For ideal tuning, it would need to be almost where the honeycomb pattern stops, but that probably wouldn't resonate well. I would love to try either adding more frets (which would move the 12th fret closer to the nut, which would let us keep the bridge in the middle part of the membrane), or creating a slightly larger body. I was going to suggest a longer ukulele shape, but I suppose it would be about the same amount of plastic around the body as being round. I don't have any experience in 3D modeling yet, but I might have to learn just to tweak this. I like what I see so far!
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2. Slice the files. I used MakerWare 2.2 with at a layer height of 0.2, hexagonal infill at 30%, and 4 shells (all for additional strength). I recommend printing "PLATE 1.stl" without a raft and printing "PLATE 2.stl" with both rafts and supports.
3. Prepare your build surface. I recommend using blue painter's tape for printing the first plate as it provides just the right level of adhesion to the thin membrane that composes the first two layers of the banjo "head" that it isn't damaged during removal from the build plate. If you don't have blue tape, wash the frosted size of the acrylic plate with soap and water (to normalize adhesion) and then vigorously rub your fingers over the middle of the build plate to deposit skin oils. This will reduce adhesion under the delicate middle of the head membrane and will maintain adhesion around the perimeter.
4. Level your bed. The large, thin membrane of the head is only half a millimeter thick and is very sensitive to variations in build platform height. I recommend "hot leveling" the bed by starting the "PLATE 1" print and watching the perimeters of the first layer as the extruder lays them down to ensure that they both stick to the platform and are of a consistent width. After one or two rounds of hot leveling, the bed should be level enough to start the real print. Be sure to watch the first layer of the membrane as is goes down just to be safe.
5. Print "PLATE 2" (with both raft and supports!). The solid raft gives both sides of the neck and head a similar surface finish, which is nice, and eliminates curling on the neck. After printing, remove support material from the neck and headstock. Pay special attention to the conical holes in the headstock-- an even surface is important when tuning.
6. Drop the captive nuts into the neck and secure the headstock. Be careful not to over-tighten the bolts as they can cause the neck to crack.
7. The neck can be secured to the head using the two M4x50mm bolts nearest to the back edge of the head frame. Technically, you can skip the two closest to the membrane and use epoxy on that portion of the joint as it will be in compression (and the bolted joint is in tension). Alternately, you can secure the neck with all four bolts, though the two nearest the membrane require a lot of patience.
8. String the thing! Insert the nut into the matching gap between the neck and the headstock and tie your first string ([use these knots](http://www.ukeland.com/pages/articles/stuff/string.jpg)) to hold it in place, then add the other three strings, [following this diagram](http://www.personal.psu.edu/mat5106/blogs/mario_202c/strings2.JPG). Insert the bridge at the base of the neck, flip it to its target orientation, and then carefully slide it onto the membrane, while pulling back on the stings (too keep pressure off the edge of the membrane). The ideal location is about a third of the diameter of the body away from the edge, but try several different locations to get a feel for the different tones and volumes possible.
9. To tune, get each string close, back out the peg, and then twist it into the headstock with pressure to lock it in. Adjust the nut depth either by carving the notches or by scaling in Z in MakerWare. Add notches to the bridge after marking where the strings lie.
10. Iterate! This design is still active and has a long way to go. The next step is to eliminate the fasteners in favor of dovetail joinery. Fasteners really raise the barrier to manufacture one of these things, as they do many other projects. Additionally, the nut height, bridge geometry, webbing design, and fret and string spacing all could use optimization. I would love to see this instrument land in the hands of somebody with greater musical knowledge who can take the design the final distance.
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