Cajon Family Print Packet

Root-mode packet: public-review cajon prototype
First build: CJ-S Standard, V1 finger joint, snare option B
Status: pre-build; measurement fields are pending

Quick Start

Build only the Standard prototype first.
Make the square assembly fixture, tapa screw template, and back-panel template before cutting final stock.
Mill walnut panels to final thickness and square before joinery.
Route any inlay before assembly.
Glue the shell square, then mount the tapa with the screw template.
Validate tone, buzz, seat load, and finish before calling the packet public-ready.

Design Summary

The cajon is a six-sided closed box with one thin front plate. The back sound hole creates the Helmholtz cavity response; the tapa creates the plate response; the two couple into the bass voice. The upper tapa corners are intentionally less constrained so the corner strike creates a crisp slap.

Member	Size	Sound hole	Predicted cavity	Predicted plate
CJ-C Compact	15 x 11 x 11 in	4.0 in	107 Hz	107 Hz
CJ-S Standard	18 x 12 x 12 in	4.5 in	96 Hz	84 Hz
CJ-B Bass	22 x 14 x 14 in	5.0 in	77 Hz	60 Hz

Critical Dimensions

Feature	Dimension	Check
Outer height	18.000 in	+/-0.020 in
Outer width	12.000 in	+/-0.020 in
Outer depth	12.000 in	+/-0.020 in
Body thickness	0.750 in	+/-0.005 in
Back thickness	0.500 in	+/-0.005 in
Tapa thickness	3 mm / 0.118 in	reject inconsistent sheets
Sound hole	4.500 in diameter	+/-0.020 in
Tapa screws	#6 x 3/4 in brass	3 in spacing except slap zone

Build Flow

Stock, Inlay, and Joinery

Acclimate stock, record actual thickness, route inlay before assembly, and keep decorative cuts away from joint edges. V1 finger joint is the first prototype default; V2, V3, and V4 remain documented variants.

Shell, Tapa, and Snare

Glue the shell in a square fixture. Cut and deburr the back sound hole. Mount the tapa with the screw template and keep the upper corner slap zones loose. Tension the guitar-string snare so it engages on a medium corner slap.

Finish

Use tung oil on the tapa and satin finish on the body. Soften seating corners and avoid any finish bridge across the tapa slap-zone gap.

Validation Sheet

Test	Result	Initials
Panel thickness recorded	____	____
Shell diagonals within 1/16 in	____	____
Seat load 250 lb for 1 hour	____	____
Sound-hole diameter verified	____	____
Tapa screw pattern verified	____	____
Helmholtz frequency recorded	____ Hz	____
Plate mode recorded	____ Hz	____
Slap spectral delta recorded	____ dB	____
Snare onset set to medium strike	____	____
No unintended rattles	____	____

Public-Release Checklist

validation.csv contains measured values for CJ-S.
validation-report.md summarizes the measured outcome.
Site hero and visual BOM images use actual build photos.
Supplier prices and lead times have been rechecked.
The workbook and design.md agree on Helmholtz end correction.
Public text credits cajon tradition and avoids novelty claims about the cultural form.