KeyLab

KeyLab: Silicone Key Substructure Manufacturing Guide

KeyLab: Silicone Key Substructure for Hall Effect Switches

This guide provides instructions for manufacturing a collapsible silicone key substructure for your musical instrument. The design features a hybrid bellows-dome geometry to achieve 3mm linear travel with progressive resistance, stability, and quick spring-back. The key top is wooden with a glued magnet, pocketing into the silicone top.

Refined Geometry (Common to Both Materials)

The geometry is designed for a rounded-rectangle key (0.42" width/height protruding). It includes:

  • Overall Dimensions: Base flange: 0.6" diameter x 0.5mm thick. Total uncompressed height: 4.5mm (compresses to 1.5mm at 3mm travel). Top pocket: 0.42" x 0.42" rounded rectangle, 1.5mm deep with 0.3mm undercut lips for gripping wood/magnet.
  • Bellows Section: 2-3 accordion folds (each 1mm high, 45° angled walls). Upper fold: 0.4-0.5mm thick for low initial resistance (~50g in first 1mm). Lower folds: 0.7-0.8mm thick for ramping to ~150g at full depression. Add 4 thin vertical ribs (0.2mm wide) externally for anti-wobble.
  • Dome Integration: Upper fold transitions to a slight dome curve. Base has 0.2mm internal stop ring for precise 3mm limit.
  • Material Tuning Notes: Adjust wall thicknesses based on material firmness for desired feel. Design in CAD (e.g., Fusion 360) for a positive master.

Select Silicone Material

Dragon Skin 30 Instructions

Dragon Skin 30 (30 Shore A, translucent, 1A:1B mix by volume/weight, pot life 45 min, cure time 16 hours). Firmer for stability; use thinner upper walls if initial press feels too resistant.

Step-by-Step Manufacturing

  1. Design and Create the Master Positive: 3D print or sculpt the geometry master (PLA/resin). Oversize slightly (0.1%). Apply Ease Release™ 200.
  2. Make the Mold: Build mold box. Pour Mold Star™ 30 over master. Cure 6 hours. Demold.
  3. Prepare Dragon Skin 30: At 73°F, mix 1A:1B for 3 min. Vacuum degas 1-2 min.
  4. Pour and Cure: Apply release to mold. Pour slowly. Cure 16 hours (or post-cure with heat: 176°F/2h + 212°F/1h).
  5. Demold and Finish: Peel mold. Trim flash. Insert magnet/wood top (glue if needed).

Testing Processes

Test 5-10 prototypes for feel, stability, and durability. Use tools like a digital force gauge, calipers, and cycle tester.

Test Procedure Target
Force Curve Press key with force gauge at 1mm increments. Record resistance. ~50g initial 1mm; ramp to ~150g at 3mm. Progressive increase.
Travel Stability Measure vertical travel with calipers under load. Check for sticking. Exactly 3mm linear; <0.1mm lateral wobble.
Spring-Back Release after full depression; time return. Repeat 100x. Full rebound <0.5s; no deformation after cycles.
Durability Cycle 1000+ compressions at 1Hz. Inspect for tears/wear. No failure; maintain force curve.
Feel Test Blind user trials on instrument. Rate lightness, progression, stability. High scores for musical expressiveness.

Iterate: If too stiff, thin upper walls by 0.1mm or add 5% thinner.

Smooth-Sil 945 Instructions

Smooth-Sil 945 (45 Shore A, purple opaque, 10A:1B mix by weight, pot life 25 min, cure time 6 hours). Firmer overall; use slightly thinner walls (e.g., upper 0.3-0.4mm) for lighter initial feel while leveraging higher rigidity for anti-wobble.

Step-by-Step Manufacturing

  1. Design and Create the Master Positive: Same as above. Adjust for firmer material: Thinner upper walls in design.
  2. Make the Mold: Same as above, using Mold Star™ 30.
  3. Prepare Smooth-Sil 945: At 73°F, mix 10A:1B by weight for 3 min. Vacuum degas 1-2 min (shorter pot life, work quickly).
  4. Pour and Cure: Apply release. Pour slowly. Cure 6 hours (faster; optional heat post-cure if needed).
  5. Demold and Finish: Peel mold. Trim flash. Insert magnet/wood top.

Testing Processes

Same core tests as Dragon Skin, but expect higher baseline resistance due to firmness. Adjust targets slightly upward if needed.

Test Procedure Target
Force Curve Press with force gauge at increments. ~60-80g initial 1mm; ramp to ~180-200g at 3mm.
Travel Stability Measure travel under load. 3mm linear; <0.05mm wobble (firmer aids stability).
Spring-Back Release and time; repeat cycles. Full rebound <0.4s; excellent due to higher modulus.
Durability 1000+ cycles at 1Hz. Superior tear resistance; no wear.
Feel Test User trials. Balanced firmness for precise control.

Iterate: If too firm, reduce wall thicknesses or switch back to softer material.