The Home Depot Toy Piano Project
September through December 2003
Sound board
Material
We use aluminum tubing with a ½” external diameter and 1/16” wall thickness. It is available from Home Depot in 3 feet sections for about $4.00 each. This project required 10 sections.
The board that holds these 37 sections is made from ¼” plywood.
Sound pieces
Cut a piece of tubing and adjust its length to the closest semitone using a chromatic tuner. Using the chosen aluminum tubing, it was found that a 293mm long section is a perfect G#5.
From this reference, we can predict the lengths of the 36 remaining tubes using the following:
notes
= (-8:28); % i.e. using G#5 as reference and going from C5 to C8)
lfact
= sqrt(2.^(-notes/12)); % i.e. length follows the square root of frequency
lengths
= 293*lfact;
|
Note |
Lgth (mm) |
Node (mm) |
Note |
Lgth (mm) |
Node (mm) |
Note |
Lgth (mm) |
Node (mm) |
Note |
Lgth (mm) |
Node (mm) |
|
C5 C#5 D5 D#5 E5 F5 F#5 G5 G#5 A5 |
369 359 348 339 329 320 310 302 293 285 |
83 81 78 76 74 72 70 68 66 64 |
A#5 B5 C6 C#6 D6 D#6 E6 F6 F#6 G6 |
277 269 261 254 246 239 233 226 220 213 |
62 60 59 57 55 54 52 51 49 48 |
G#6 A6 A#6 B6 C7 C#7 D7 D#7 E7 F7 |
207 201 196 190 185 179 174 169 164 160 |
47 45 44 43 42 40 39 38 37 36 |
F#7 G7 G#7 A7 A#7 B7 C8 |
155 151 147 142 138 134 131 |
35 34 33 32 31 30 29 |
In total, this requires 8.513 m of tubing (about 29 feet). Each piece might need slight adjustment (filing) to be tuned to the desired pitch. The tubes are then drilled (5/64 drill bit) at the node locations (i.e. 22.5% of the length from either ends). Two small pieces of self-adhesive felt are also placed at node locations.
Key / Hammer Mechanism
Material
The main arm of the hammer mechanism is made from ½x3/4” sections.
The “one way joint” at the end of the arm uses small pieces of a flexible but robust vinyl fabric (from the Childrens’ Museum recycle store)
The striking head is attached to the main arm via 14-gauge steel wire.
The white keys are cut from ¼” plywood and the black keys are made from the same 1/2x3/4” sections as the main arm.
The axle of the 37 keys is a ¼” diameter aluminum rod (available from HomeDepot in 3 feet sections for $3 or $4).
All assembly consists principally of wood glue and small ½” wire nails for the on-way joint.
Hammer arm and one-way joint
Two “stops” parts are designed to limit the range of rotation to the arms to a [0º, 7º] range.
Additionally, continuous contact with the sounding tubes should be avoided. Therefore after the arm launches the hammer towards the tube, it is desired that the hammer freely backs away from the tube even if the key is fully pressed down. This is achieved by means of a one way joint allowing the hammer to swing freely past the rotation of the arm.
Key and hammer layout
With white keys that are 1” wide, an octave (i.e. 12 notes and therefore 12 hammers) spans 7”. The uneven distribution of the actual keys’ width requires the 12 (evenly distributed) hammers to be shaped unevenly.
Main Frame / Body
Material
The frame consists mainly of ½” Birch plywood, available from HomeDepot in 2x4’ for $16 each. Two of those are needed.
The principal structural joints use metal angle brackets and #8 ½” metal screws.
All other assembly consists of wood glue, #6 1” and #6 ¾” wood screws.
Finishing touches
Christmas 2003
