--- instrument: Glass Armonica family: idiophone_friction_glass packet_mode: v5_l2_concept authority: pending_measurement readiness: L2 concept / pending-measurement packet --- # Glass Armonica Design Study ## Design Thesis This study captures a Franklin-style glass armonica as a low-stakes V5 L2 instrument packet. The instrument uses a stack of graduated glass bowls on a single horizontal spindle. A treadle-driven flywheel rotates the spindle, and the player sounds the wetted rims with fingers instead of striking or bowing. The packet intentionally stops before fabricated geometry. The L2 uplift adds a reviewable subsystem model and a candidate part ledger so future measurement can land in the right places without pretending that pitch, bowl spacing, spindle diameter, drive ratio, or shop geometry is known. ## Mechanism The central assembly is a horizontal shaft carrying nested glass bowls from large/low to small/high. Each bowl needs a non-marring support interface, positive axial registration, and clearance from neighboring bowls so a vibrating rim can speak without rubbing. The drive train is treadle first: a foot pedal moves a linkage or belt that turns a flywheel, which smooths the motion before it reaches the spindle. The drive must be quiet enough not to mask the glass tone and gentle enough to avoid shock loads into the bowl stack. The playing interface is wetted-finger friction. Water management is part of the instrument, not an accessory: the concept needs a tray, wipe area, drip path, and guarding plan so moisture stays away from bearings, belts, and finished wood. ## L2 Subsystem Plan - Bowl stack: identify real bowls first, then measure free response, rim profile, mass, and safe mounting surfaces before any nesting layout is drawn. - Spindle and mounts: prototype non-marring interfaces on sacrificial samples before choosing a shaft, collar, cone, gasket, or clamp strategy. - Drive train: compare treadle, belt, flywheel, and bearing noise as a separate bench rig before coupling it to glass. - Wetting station: keep water delivery, drip capture, wipe storage, and bearing isolation in the same subsystem so moisture hazards stay visible. - Guarding: treat rotating glass, belt motion, and cleanup as first-order design inputs, not finish details. ## Parametric Intent The future design table should separate measured values from design choices: - `bowl_id` - `measured_bowl_outer_diameter` - `measured_rim_profile` - `measured_wall_thickness_profile` - `measured_bowl_mass` - `measured_free_pitch` - `measured_mounted_pitch` - `spindle_interface_status` - `nesting_clearance_status` - `wetting_response_status` - `guarding_status` - `drive_noise_status` - `water_intrusion_status` - `bowl_serviceability_status` All values above are currently `pending_measurement`. This packet does not infer them from historical examples, photos, or prose. ## Authority Boundary - Concept authority: this repository's README, design notes, decision record, and estimated BOM. - Measurement authority: none yet. - CAD/DXF authority: none yet. - Tuning authority: none yet. No future rendering, concept sketch, or image prompt should be treated as a source for bowl spacing, spindle diameter, drive ratio, rim profile, pitch, or toolpaths. ## Measurement Gates Promotion beyond L2 requires: - A real bowl candidate measured for geometry, mass, and free response. - A non-destructive mounting test that does not chip, pinch, or overload the glass. - A quiet bearing and drive mockup that can rotate smoothly under treadle power. - A wetting test that confirms tone onset, water control, and player ergonomics. - A safety review for rotating glass, pinch points, belt paths, and cleanup. - A cut-list review where every part is tied either to measured bowl data or to an explicit pending-measurement gate. ## Risks - Glass fracture from clamping, thermal stress, impact, or spindle misalignment. - Treadle vibration coupling into the bowl stack. - Water intrusion into bearings, belts, wood, or electrical accessories. - Bowl-to-bowl contact if nesting clearance is not measured under rotation. - Overconfident pitch claims before real bowls are measured in mounted and unmounted states.