Skateboard Banjo
Project Plan
Use old skateboard decks to make the neck (and other parts) of a tenor banjo. A skateboard deck has a natural bend at the kicktail for the headstock making the underside of the deck a slightly convex fretboard due to the deck's concave. Skate decks are typically 7-ply Canadian Maple and are very stiff. I will be laminating two decks together for extra depth and stiffness.
General
- http://en.wikipedia.org/wiki/Banjo
- Hmmm, 5-string or Tenor? I'd love a 5-string so I'll try to make that work
- compare with commercially available, e.g. Ozark: 2102G 5-String Open Backed Banjo (Scale length - 697mm = 27.45")
- NB: I have no idea what I'm doing!
- neck: this is the skate deck part - I have two identical old decks (same pressing, same concave) which I've glued together with Gorilla Glue (see pics)
- body/pot: I'm going to use a wooden hand drum with tensioners which will give me a basic body for little cost and little work. In the future I want to glue up and turn my own rims on the lathe.
- bridge: current thinking - just a piece of skate deck
- nut: current thinking - just a piece of skate deck
- tuning hardware: ebay cheapest set of 6 guitar tuners 3x left 3x right
- strings: whatever becomes available
- tensioning bars: I'll see how the hand drum and neck come together
- tailpiece: cheapest ebay magic!
Geometry, plans and other info: -
| Banjo | # frets | scale |
|---|---|---|
| Gibson 26-1/4" | 22 | 26.250" |
| Long-neck 32-1/4" | 25 | 32.250" |
| Tenor 22-1/4" | 19 | 22.250" |
| Vega 27" | 22 | 27.000" |
- a Tenor banjo has 19 frets and a 22.250 inch scale
- http://www.stewmac.com/FretCalculator
| fret | from nut | fret to fret |
|---|---|---|
| 1 | 1.249" | 1.249" (nut-1) |
| 2 | 2.428" | 1.179" (1-2) |
| 3 | 3.540" | 1.112" (2-3) |
| 4 | 4.590" | 1.050" (3-4) |
| 5 | 5.581" | 0.991" (4-5) |
| 6 | 6.517" | 0.936" (5-6) |
| 7 | 7.400" | 0.883" (6-7) |
| 8 | 8.233" | 0.833" (7-8) |
| 9 | 9.020" | 0.787" (8-9) |
| 10 | 9.763" | 0.743" (9-10) |
| 11 | 10.463" | 0.700" (10-11) |
| 12 | 11.125" | 0.662" (11-12) |
| 13 | 11.749" | 0.624" (12-13) |
| 14 | 12.339" | 0.590" (13-14) |
| 15 | 12.895" | 0.556" (14-15) |
| 16 | 13.420" | 0.525" (15-16) |
| 17 | 13.916" | 0.496" (16-17) |
| 18 | 14.383" | 0.467" (17-18) |
| 19 | 14.825" | 0.442" (18-19) |
Progress
Here we have some progress photos of the deck lamination and slice-up. Note: I selected the two decks that had the most accurately matching concave without too much damage. Also, I removed the griptape! As Norm Abram says, "You can never have too many clamps". Using bamboo chopsticks as dowels to align the bolt-holes, fill them in, and perhaps add a little strength.
The skate deck glue-up has been sliced down to about 95mm wide. The nose and tail beyond the bolt-holes are about 135mm and 125mm long. The truck bolt mountings are 59mm long each and there is 350mm between the innermost bolt-holes. The bolt-holes are 35mm between (46.5mm including holes).
The nut is to be located immediately before the kicktail starts to drop away. A centre line is scribed that also defines the location of the third string. The scale length will be decided when the hand drum is obtained and the neck-body join is decided.
The width of the neck at the nut is 1 1/4 inch on a lot of banjos I've seen but I think I'd like to use 1 3/8 inch to be more like my ukulele. This width will fall almost exactly between the bolt-holes.
- 35 millimeter = 1.377 inch and 1.375 inch (1 & 3/8) = 34.925 millimeter
The neck at the nut will be slightly offset from the centreline due to the asymmetric narrowing after the 5th string. The width where the neck meets the body is yet to be decided.
The width of the headstock will be decided largely by the string tensioning hardware and the aesthetics of whatever skate-style I can incorporate (e.g. a rounded head like modern popsicle decks or something more old-school)
Neck and pot mounting: I watched some yoochoob vids on the subject and for my purposes I'm going to have to see how things look when I get the hand drum (ebay bid in progress!). What is immediately clear is that the neck thickness needs to be increased where it joins the pot (forgot what the name of that bit is!)
Metric Scale Length
596 mm fret scale fret | from nut | fret to fret 1 | 33.451 mm | 33.451 mm (nut-1) 2 | 65.024 mm | 31.573 mm (1-2) 3 | 94.826 mm | 29.802 mm (2-3) 4 | 122.954 mm | 28.128 mm (3-4) 5 | 149.504 mm | 26.550 mm (4-5) 6 | 174.564 mm | 25.060 mm (5-6) 7 | 198.218 mm | 23.654 mm (6-7) 8 | 220.544 mm | 22.326 mm (7-8) 9 | 241.616 mm | 21.072 mm (8-9) 10 | 261.506 mm | 19.890 mm (9-10) 11 | 280.280 mm | 18.774 mm (10-11) 12 | 298.000 mm | 17.720 mm (11-12) 13 | 314.725 mm | 16.725 mm (12-13) 14 | 330.512 mm | 15.787 mm (13-14) 15 | 345.413 mm | 14.901 mm (14-15) 16 | 359.477 mm | 14.064 mm (15-16) 17 | 372.752 mm | 13.275 mm (16-17) 18 | 385.282 mm | 12.530 mm (17-18) 19 | 397.109 mm | 11.827 mm (18-19) 20 | 408.272 mm | 11.163 mm (19-20) 21 | 418.808 mm | 10.536 mm (20-21) 22 | 428.753 mm | 9.945 mm (21-22)