Cajón

Cajón

Cajón

Cajón
Design - Fabrication
Conçu et fabriqué par:
Tomi Murovec
FabLab Manager - UBO Open Factory

Publication : 28 sept 2018

Le cajón est un instrument de musique inventé au Pérou au xviiie siècle. Il fut très certainement à ses débuts une caisse destinée à la cueillette des fruits ou à la pêche des poissons, les esclaves n'ayant pas accès à autre chose que les matériaux rustiques. Le cajón actuel possède généralement un élément de plus, le timbre, qui rend le son proche de celui d'une caisse claire de batterie.

Le cajón est une caisse de résonance parallélépipède, de 50cm x 30cm x 30cm (hauteur/largeur/profondeur) en moyenne. La plaque de frappe (devant) est plus fine que les autres côtés, ce qui permet une élasticité et une résonance propre au cajón. Au dos, un trou d'environ 10cm de diamètre permet la sortie du son (même effet qu'un évent de décompression d'une enceinte de sono). Un timbre situé sous la plaque supérieure vibre lors de la frappe de l'instrument. Il permet de différencier les cajones, tout en donnant au son cette ressemblance à la caisse claire de la batterie. Il peut être constitué :

Certains cajones n'ont pas de timbre ce qui donne un son ressemblant plus au son type bongo. Le cajón typique du flamenco a le haut de la surface de frappe (face avant) non fixé sur la partie supérieure ce qui lui donne un son claqué. Cet instrument fait à présent partie intégrante de la pédagogie musicale active Orff-Schulwerk.

La société Natur Concept à Boulazac Isle Manoire produit un cajón en carton pliable et biodégradable ! (Source : Wiki)

Design - 3D Model

The design was created using a 3D modelling software - Autodesk Fusion360. It features a wooden frame consisting of 4 plates of 18 mm plywood (Picture 1). The front and back plates (Picture 2) are designed to be fabricated using 3 mm "peuplier" plywood because of its lightness. A snare adjustment mechanism (Picture 3) was designed to permit the player to adjust the angle, and thus the force that the snare wires push against the front plate. This enables the adjustment of the snare effect by adjusting the angle of the snare wires from the vertical position (0°) to horizontal position (90°), where the snare wires are fully engaged, producing the maximum snare effect. The adjustment is made by rotating the adjustment wheel on the left side of the Cajón (Picture 4).

The front and back plate designs were additionally designed to be cut and engraved by a laser cutting machine (Picture 5 and 6).

Photos
Picture 1: Frame Design
Picture 1 : Frame design.
Picture 2: Back (left) and front (right) plate design.
Picture 2 : Back (left) and front (right) plate design.
Picture 3 : Snare adjustment mechanism
Picture 3 : Snare adjustment mechanism
Picture 4 : Snare adjustment wheel on the left side of the Cajón
Picture 4 : Snare adjustment wheel on the left side of the Cajón
Photos
Picture 5 : Front plate design.
Picture 5 : Front plate design.
Picture 6 : Back plate design
Picture 6 : Back plate design.

Fabrication

The 4 plates for the frame were fabricated using a CNC machine and 18 mm plywood. The side (vertical) plates feature two 18 mm holes for the axis and a 8 mm holes for the connection between the adjustment wheel and the small adjustment gear. The big gear, connected to the snare axis was fabricated using the laser cutting machine and 10 mm plywood and was glued to the axis. The axis was inserted in the pre-cut holes and the whole frame was glued together and left overnight to dry (Picture 7).

The small gear features a hexagonal pocket for the insertion of a standard M8 nut, which allows for a rigid connection between the adjustment wheel bolt (Picture 9, left) and the gear. The part was 3D printed using Ultimaker 2 Extended+ printer and white PLA material (Picture 8). A flathead bolt (Picture 9, left) was used to provide a rigid connection between the adjustment wheel (Picture 9, right) and the small gear. Additionally, a second nut was added to lock the connection and adjust the resistance of the adjustment wheel (Picture 8).

The front and back plates were fabricated using the laser cutting machine and were attached to the frame using 14 wood screws for each plate (Picture 10).

The snare wires were bought at a local music store and cut into two halves before being attached to the wooden axis.

When the assembly was finished, all the edges were adjusted using a router, resulting in a smooth surface transition between all the components (front, back plate and the frame). All the surfaces were then sanded using a fine grit sand paper (#180 and then #240) before protecting the wood with a wood protection oil (matte). The oil was left to dry for two hours. The surface was sanded again using #240 sand paper before applying the second layer of oil and left overnight to dry (Picture 11). The surface was then sanded for the last time using #500 sand paper, resulting in a smooth matte finish.

The final stage was the addition of small rubber feet (Picture 12). The feet were designed as a circular disc with a 20 mm diameter and 3 mm height. They were printed with a MakerBot Replicator 2X 3D printer using a NinjaFlex flexible material, providing a good stability and preventing the sliding of the Cajón.

Fabrication
Picture 7
Picture 7 : Four plates of plywood (18 mm) were glued together, forming the frame for the Cajón. Additionally, the mechanism for adjusting the snare angle was added at the same time.
Picture 8
Picture 8 : The mechanism for adjusting the snare angle, comprising of two gears; large one connected to the axe with the snare, and a small one, connected to the adjustment wheel on the external side of the Cajón.
Picture 9
Picture 9 : Bolt (left) and the adjustment wheel (right).
Picture 10
Picture 10 : The front and back plate were fabricated using the Laser cutting machine and were attached to the base using 14 wood screws.
Picture 11
Picture 11 : The assembled Cajón was polished using a fine sand paper (#240) and then protected using oil for wood.
Picture 12
Picture 12 : 3D printed feet.

Finished Cajón

Photos
 

Egalement dans cette section

Fauteuil en carton

Modélisation 3D, construction des plans, découpe laser et assemblage d'un fauteuil en carton.
Logiciels utilisés : Fusion 360 + Slicer for Fusion 360 + Visicut

 

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UBO Openfactory

Salle D133 Bâtiment D

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Fait avec  par la Team UOF