ADR-011: Laminated Plinth Baseboard

Status

Accepted

Context

The Amalgam is a heavy machine: - M12 iron skeleton: ~15kg - 3x Z-motors + geared extruder: ~3kg - Total build weight: ~18-20kg

A “Naked Frame” (frame sitting directly on workspace) has limitations: 1. Vibration Transmission: Frame acts as speaker for motor noise 2. Portability Issues: Picking up frame can flex/twist it 3. High-Frequency Resonance: Can cause ringing/ghosting 4. Floor Interaction: Uneven surfaces affect frame squareness

At the same time, a well-grounded mass is an engineering advantage—mass damps vibration. The question is how to anchor that mass properly.

Decision

We adopt a Laminated Plinth Baseboard as the Tier 3 Reference Spec foundation, using Constrained Layer Damping (CLD) to convert motor vibrations into microscopic heat.

Architecture

The Plinth: Two 18mm MDF boards (36mm total thickness) glued together with viscoelastic adhesive.

Construction:

┌─────────────────────────────────────┐
│   Top MDF Board (18mm)              │
│   ↓                                 │
│   Viscoelastic Glue Layer (CLD)     │ ← Converts vibration to heat
│   ↓                                 │
│   Bottom MDF Board (18mm)           │
│   ↓                                 │
│   Rubber Feet (4x corners)          │
└─────────────────────────────────────┘

Frame Attachment: - M12 rods pass through drilled holes in plinth - Secured with large fender washers + M12 nuts on underside - Frame bolts down to plinth (through-bolted) - Z-pucks either clamped to rods (Naked) or screwed to MDF (Tier 3)

Why Laminated?

1. Constrained Layer Damping (CLD) - When motors vibrate, they send sound waves through plinth - Glue layer is stretched/compressed (shear strain) - Mechanical friction in glue converts kinetic energy to heat - Result: Vibration “dies” in glue instead of ringing through frame

2. Glue Choice Matters - Standard PVA Wood Glue: Dries hard → very stiff but poor damping - Green Glue / Construction Adhesive: Stays slightly rubbery → maximizes energy conversion (acoustically dead) - Viscoelastic: The gold standard for CLD in industrial/audio applications

3. Massive Inertia - 36mm MDF slab anchored to M12 frame creates ~20kg+ workstation - Provides heavy ballast resisting high-acceleration moves - Machine won’t budge or twist during operation

4. Rods Become Alignment Rails - Without plinth: M12 rods carry total weight (suspended load) - With plinth: MDF handles weight, rods ensure X/Y gantry square to bedrock - Shifts from “support” role to “alignment” role

Foundation Strategy Levels

Configuration Effort Stability Resonance Peak Recommended For
Naked Frame (No pads) Low Moderate High (Ringing) Emergency/Tier 1
Naked + Rubber Pads Low High Medium Tier 1-2
Single MDF Board Medium Very High Low Tier 2-3
Laminated Plinth High Industrial Negligible Tier 3 Reference

Z-Puck Mounting on Plinth

The Zero-Flex Anchor: - Z-pucks use flanged design screwed directly into MDF - Slotted mounting holes allow alignment adjustment - MDF acts as massive vibration sink for Z-motors (which move most weight)

The Hybrid Anchor: - Even with plinth mounting, use Double-Nut Anchor (see ADR-010) - M12 rod passes through puck + MDF, locked by nuts - “Handshakes” iron skeleton to plinth - Accommodates MDF expansion/contraction from humidity

Consequences

Benefits

  • Industrial Silence: Negligible resonance, no ringing/ghosting
  • Structural Rigidity: Frame bolted to massive base can’t lose squareness
  • Portability: Easier to move—pick up by plinth, frame stays square
  • Vibration Isolation: Z-motor vibrations sink into plinth, don’t reach print
  • Thermal Stability: MDF is less affected by ambient temperature swings
  • Professional Feel: Machine becomes “industrial tool” rather than “toy”

Trade-offs

  • Weight: Final machine ~20-25kg (very heavy)
  • Assembly Effort: Requires woodworking (cutting, drilling, gluing)
  • Space: Larger footprint than naked frame
  • Cost: Adds $20-30 AUD for MDF + adhesive
  • Lead Time: Glue needs 24hr cure before drilling
  • Permanent: Once built, machine is semi-permanent workstation

What This Enables

  • Tier 3 Reference Spec: Industrial-grade ±0.1mm accuracy
  • Perfect First Layers: Vibration-free foundation aids leveling
  • Engineering Materials: ABS, PC, Nylon benefit from stable environment
  • Quiet Operation: Combined with software, machine is near-silent

What This Replaces

  • Naked frame with rubber pads
  • Need for perfectly flat workspace (plinth compensates)
  • Frequent frame re-squaring

BOM Implications (Generic)

Scenario A: Tier 1-2 Builds (Naked Frame)

  • Recommended: Rubber pads under corners only
  • Cost implication: Very Low (+$10-15 AUD)
  • Assembly: No woodworking required
  • Performance: Good enough for hobby printing

Scenario B: Tier 2-3 Upgrade (Single Board)

  • Parts needed:
    • 1x 18mm MDF board (cut to script dimensions)
    • 4x M12 nuts + fender washers (for frame thru-bolting)
    • Optional: Z-puck wood screws
  • Cost implication: Low (+$15-20 AUD)
  • Assembly: Cut board, drill using template
  • Performance: Very good, significant vibration reduction

Scenario C: Tier 3 Reference (Laminated Plinth)

  • Parts needed:
    • 2x 18mm MDF boards (cut to script dimensions)
    • 1x Tube viscoelastic adhesive (Green Glue or construction adhesive)
    • 6x Wood screws (for Z-pucks, if not clamped to rods)
    • 4x Large fender washers (50mm+ dia)
    • 4x M12 nuts + washers (underside of MDF)
    • 4x Rubber feet (for plinth corners)
  • Cost implication: Low (+$20-30 AUD)
  • Assembly:
    • Glue boards together (24hr cure)
    • Drill holes using build123d template
    • Thru-bolt frame to plinth
    • Mount Z-pucks
  • Performance: Industrial-grade, negligible resonance

Donor Compatibility

  • All donors: Plinth is independent of donor parts
  • Salvage Benefit: Donor printers often have beds that need stable platform

Implementation Notes

MDF Dimensions (from build123d)

PLINTH_X = SKELETON_X + 100  # 50mm overhang each side
PLINTH_Y = SKELETON_Y + 100  # 50mm overhang each side
PLINTH_Z = 36mm              # 2x 18mm boards

For 250mm³ build volume (MK52): - Frame: ~550mm × ~370mm - Plinth: ~650mm × ~470mm × 36mm

Build Procedure

Phase 1: Preparation 1. Cut both MDF boards to exact dimensions 2. Clean surfaces (remove dust) 3. Clamp boards together evenly 4. Apply viscoelastic adhesive in serpentine pattern (approx. 3mm bead) 5. Re-clamp with even pressure 6. Cure 24 hours (follow adhesive spec)

Phase 2: Drilling 1. Use build123d-generated drill template 2. Template includes: - M12 rod hole positions (8 total: 4 front, 4 rear) - Z-puck mounting positions (3 front, 0 rear if clamped) - Corner hole for fender washers (4) - Alignment marks for frame placement 3. Drill all holes with appropriate bits: - M12 holes: 12.5mm drill bit - Puck screws: Pilot bit matching screw size - Fender washers: Clearance holes

Phase 3: Assembly 1. Place plinth on rubber feet 2. Insert M12 rods through plinth holes 3. Install fender washers + nuts underneath (hand-tight) 4. Assemble corner brackets onto rods 5. Position Z-pucks: - If clamped: Slide onto rods, use double-nut anchor (see ADR-010) - If screwed: Position on MDF, use slotted holes for alignment 6. Home bed, align Z-pucks to lead screws 7. Tighten all connections fully: - M12 thru-bolts: 15-20 ft-lbs - Z-puck clamps: 2-3 Nm - Puck wood screws: Firm, don’t strip MDF

Phase 4: Validation 1. Verify frame is level on plinth 2. Check all M12 nuts are tight 3. Tap plinth - should sound “dead”, not ringing 4. Perform Z-tilt calibration 5. Print test tower, check for resonance

Drill Template Features

The build123d script generates a printable template: - Full-size paper template: Tape to MDF for drilling - Alignment marks: Ensures consistent positioning - Hole size labels: Confirms drill bit selection - Z-puck slot positions: Pre-marked for puck mounting

Counter-Sinking (Optional)

For flush underside: - Counter-sink M12 nuts 5mm into bottom board - Use template to mark positions before gluing - Result: Machine sits perfectly flat on workbench

Environmental Considerations

  • Humidity: MDF expands/contracts - use Hybrid Anchor with double-nuts
  • Moisture: Keep plinth dry, consider sealing edges with paint/varnish
  • Temperature: MDF is stable, but avoid extreme heat sources

Safety Considerations

  • Dust: MDF dust is harmful - use mask/ventilation when cutting/drilling
  • Weight: Get help moving 36mm plinth - it’s very heavy
  • Adhesive: Follow manufacturer safety instructions (PPE, ventilation)
  • Torque: Don’t over-tighten M12 nuts into MDF - may pull through

References

  • docs/reference/ai-conversations/baseboard.md: Complete technical discussion
  • docs/adr/010-floating-z-puck.md: Z-puck mounting on plinth
  • docs/adr/001-m12-skeleton.md: Frame architecture
  • ../manifesto.md: “The Bed is the Anchor; the Plinth is the Bedrock” pillar
  • ../manifesto.md: Tier 3 Reference Spec

Evolution Notes

This ADR establishes the laminated plinth as the optimal foundation for Tier 3 builds. The plinth concept can be adapted for different applications (e.g., enclosed build chamber, heated build chamber) while maintaining CLD principles.

Related Standards: - CLD widely used in automotive, aerospace, and high-end audio - Green Glue Noiseproofing Compound: Commercial viscoelastic adhesive - Industrial machine tools often use similar laminated bases