ADR-028: Target Filament Selection

Status

Accepted

Context

Amalgam is a scavenger-friendly printer built from donor parts. The choice of target filaments affects every hardware decision—hotend, extruder, bed temperature capability, and whether exotic upgrades like enclosures or hardened nozzles are needed.

The project follows an 80/20 philosophy: optimize for the filaments that cover 80-90% of real-world use cases, rather than chasing edge cases that require expensive upgrades.

What Donors Provide

Most donor printers (Anet A8, Ender 3, Prusa clones, i3 Mega) shipped with: - Hotends: PTFE-lined, max ~240°C safely - Beds: 12V or 24V, capable of 60-100°C - Extruders: Basic single-drive, often with brass drive gears - Nozzles: Brass, 0.4mm

This hardware handles PLA and PETG reliably. TPU is possible with care. ABS pushes bed temperatures and benefits from enclosures most donors lack.

The E3D V6 Upgrade (ADR-004)

Amalgam specifies the E3D V6 all-metal hotend, which: - Handles temperatures up to 285°C safely - Eliminates PTFE degradation concerns - Opens the door to ABS, ASA, and some exotics

However, having capability doesn’t mean we should optimize for it.

The Pitan Extruder (ADR-019)

The Pitan extruder provides: - 3:1 gear reduction for consistent extrusion - Single-drive simplicity (scavenged NEMA17) - Adequate grip for flexible filaments at moderate speeds

This handles PLA, PETG, and TPU well. Highly flexible TPU (Shore 85A and below) may require slower speeds.

Decision

Amalgam’s target filaments are:

Filament Priority Bed Temp Hotend Temp Notes
PLA Primary 50-60°C 190-220°C Default material, widest compatibility
PETG Primary 70-85°C 230-250°C Structural parts, outdoor use
TPU Primary 40-60°C 220-240°C Flexible parts, grips, bumpers

These three filaments are the reference specification. Amalgam is optimized for them.

Why These Three?

1. They Cover 80-90% of Use Cases

Use Case Best Filament Why
Prototypes, models, enclosures PLA Cheap, easy, looks good
Functional parts, brackets, housings PETG Strong, heat-resistant, layer adhesion
Outdoor parts, UV exposure PETG Better UV resistance than PLA
Phone cases, grips, bumpers TPU Flexible, impact-absorbing
Gaskets, seals, vibration dampening TPU Compressible, durable
Printer parts (non-heated) PETG Survives ambient chamber temps

The vast majority of home 3D printing falls into these categories.

2. Donor Hardware Handles Them

  • Beds: 60-85°C is well within donor bed capability
  • Hotends: 190-250°C is safe even for PTFE-lined donors (though we use V6)
  • Extruders: Single-drive handles all three; TPU just needs slower speed
  • Nozzles: Brass works fine; no hardened nozzle needed

No exotic upgrades required. Donors provide what’s needed.

3. No Enclosure Required

PLA, PETG, and TPU print reliably in open air: - No warping concerns (unlike ABS) - No toxic fume concerns at normal temps - No heated chamber needed

This keeps build complexity low and avoids the cost/effort of enclosure construction.

4. Widely Available and Cheap

Filament Typical Price (AUD/kg) Availability
PLA $18-30 Everywhere
PETG $22-35 Everywhere
TPU $30-50 Common

No specialty suppliers needed. Hardware stores, office supply chains, and online retailers all stock these.

Filaments That Work But Aren’t Optimized For

Filament Bed Temp Hotend Temp Challenges
ABS 90-110°C 230-260°C Warping without enclosure, fumes, bed adhesion
ASA 90-110°C 240-260°C Same as ABS, slightly better UV
Nylon (PA) 70-90°C 250-270°C Hygroscopic, needs drying, enclosure helps
PC 100-120°C 270-310°C Very high temps, warping, enclosure required
Carbon-filled Varies Varies Requires hardened nozzle

These are possible but not the target. Users can experiment, but: - ABS/ASA: Expect warping without enclosure; use brim, draft shield - Nylon: Dry filament thoroughly; expect challenges - PC: Pushes V6 to its limits; enclosure strongly recommended - Carbon-filled: Will wear brass nozzle; upgrade to hardened steel

The Amalgam spec doesn’t prevent these—it just doesn’t optimize for them.

Filaments Explicitly Not Supported

Filament Why Not
PEEK/ULTEM Requires 350°C+ hotend, all-metal construction, heated chamber
Metal/Wood-filled Niche, requires hardened nozzle
Highly flexible TPU (<85A) May need direct drive or very slow speeds

These require hardware beyond the scavenger spec.

Consequences

Benefits

  1. Maximizes donor reuse: No exotic upgrades needed for primary filaments
  2. Low barrier to entry: PLA/PETG/TPU are beginner-friendly
  3. Cost-effective printing: Cheap, widely available materials
  4. Reliable results: These filaments are well-understood, documented
  5. No enclosure needed: Simpler build, lower cost
  6. Safe operation: No toxic fumes at normal temperatures

Trade-offs

  1. ABS not optimized: Users wanting ABS should consider enclosure addition
  2. High-temp materials limited: PC, Nylon need care and upgrades
  3. Abrasive filaments wear nozzle: Carbon-fill users should buy hardened nozzles

What This Means for the Build

Component Implication
Hotend (V6) 285°C max is plenty; no upgrade needed
Bed 60-85°C target; all donors handle this
Extruder (Pitan) Single-drive adequate; no dual-drive needed
Nozzle Brass is fine; hardened optional
Enclosure Not required for reference spec
Drying Nice to have for PETG, not critical

BOM Implications

Reference Build (PLA/PETG/TPU)

No additional parts beyond standard Amalgam spec: - E3D V6 hotend (or clone) — already specified (ADR-004) - Pitan extruder — already specified (ADR-019) - Donor heated bed — already specified (ADR-024) - Brass 0.4mm nozzle — comes with V6

Additional cost for filament focus: $0

Optional Upgrades for Expanded Materials

Upgrade Enables Cost (AUD)
Hardened steel nozzle Carbon-filled, glow-in-dark $8-15
Enclosure (DIY) ABS, ASA, Nylon, PC $30-80
Filament dryer Nylon, PETG (improved) $40-80
All-metal heatbreak upgrade Higher temps (if using clone V6) $10-20

These are user-choice upgrades, not part of reference spec.

Filament Storage Note

While not strictly part of this ADR, builders should know: - PLA: Tolerates humidity reasonably well - PETG: Benefits from dry storage; slight moisture causes stringing - TPU: Quite tolerant of humidity

A sealed container with desiccant is good practice but not critical for these three filaments.

References