The Self-Replication Index
“Self-replicating” without P%/M%/C% is marketing. This calculator scores any machine on three dimensions: what fraction of its own parts can it produce — by part count (P%), by mass (M%), and by cost (C%)? C% is the honest one.
Proportion of discrete BOM parts the machine can self-produce. Cheap to compute. Easy to game — print many small clips to inflate the count.
Proportion of finished copy's mass the machine produces. Favours machines that print their own frames. Penalises heavy bought components (motors, batteries).
Proportion of BOM cost at arm's-length market prices. The honest one — always the lowest of the three. Printed plastic is cheap; bought ICs and motors are expensive.
Index (6 machines scored)
| Machine | Class | P% | M% | C% | T_h (hrs) | BOM ($) |
|---|---|---|---|---|---|---|
| RepRap Mendel | Class 3 | 45.0% | 16.0% | 5.0% | 20 | $400 |
| Tesla Optimus (internal) | Class 4 | 95.0% | 89.5% | 5.0% | — | $50,000 |
| Prusa MK4 | Class 3 | 30.0% | 9.2% | 2.7% | 10 | $450 |
| Bambu Lab X1 Carbon | Class 4 | 3.3% | 1.4% | 0.4% | 1 | $1,200 |
| Voron 2.4 350mm | Class 3 | 30.4% | 8.3% | 0.0% | 30 | $1,230 |
| HUMA Kit 01 (Entry) | Class 4 | 0.0% | 0.0% | 0.0% | 150 | $11,172 |
The Honest Number Is Always C%
Every machine scores highest on P% (easy to print many small parts) and lowest on C% (the expensive parts — motors, electronics, bearings — are always bought). The Prusa MK4 prints 30% of its own parts by count but only 3% by cost. That 27-point gap between P% and C% is the gap between marketing and reality. Any claim of “self-replication” that doesn't disclose C% is incomplete.