What does a wooden rod cost a printer in stiffness?
research/selfrep-rodbeam
Beam model of the Prusa Mendel's smooth rods: a wooden rod sags 20 times a steel one at 8 mm and needs about 17 mm to match it, and selfrep-redesign's assumed dowel mass was twice the geometric one (stylised).
What it found
Replaces the assumed penalty of selfrep-redesign’s wooden-rod substitution with Euler–Bernoulli beam theory. At 8 mm a hardwood rod sags 20× a steel one (the modulus ratio) and a printed PLA rod 80×; matching steel stiffness needs about 17 mm of hardwood, outside the printer’s 8 mm hardware, while a 1–2 mm sag tolerance needs 9–11 mm. The earlier 30 g per dowel was about twice the geometric 13.8 g, moving mass closure from 35.8% to 34.6%; thicker dowels raise closure again, a quirk of counting imported feedstock as makeable. Stylised: properties and the 5 N load are assumed and no rod was tested.
A figure from its own output
Paper, code and results
More in Self-replicating manufacturing
- What natural-frequency target does a printer’s rod have to meet, and what does a wooden rod cost?Carriage natural frequency on the Prusa Mendel's smooth rods: a vibration target, not a sag limit, sets the rod diameter; hardwood needs about twice steel's diameter (stylised).
- Does an aluminium rod fit the printer where a wooden one cannot?Aluminium rods in the printer redesign: matching a steel rod's sag takes 10.4 mm aluminium (fits the assumed 12 mm holders) against 16.9 mm hardwood (does not), at 39.5% vs 37.8% mass closure (stylised).
- How stiff a rod does a frequency target need, in aluminium and in wood?Sizing printer rods to a first-mode frequency target instead of a sag spec: at 0.3 kg aluminium reaches 40 Hz with 10.0 mm (fits the assumed 12 mm holders) where hardwood needs 16.0 mm (stylised).
- How thick must a printer rod be to keep carriage ringing small at a given acceleration?Rod diameter from an acceleration and ringing budget: at 3 m/s² with abrupt steps steel needs 7.3 mm, aluminium 9.6 mm, hardwood 15.5 mm; a 20 ms force ramp cuts aluminium at 5 m/s² from 10.9 to 8.9 mm (stylised).
- Which assumed input of the replicating-printer growth model does the doubling time depend on most?Which assumed input of the replicating-printer growth model moves its doubling time (Sobol indices, stylised, assumed ranges): budget and vitamin cost together carry ~90% of the variance when imports bind; when machine time binds, failure, print rate, budget and price are comparable.
- How does a resale value for the finished fleet move the switch from copies to goods?A resale value
sper machine at the horizon shortens the goods phase from one e-folding time1/kto1/k − s/a; ats ≥ a/kthe shop never switches. Grid optimum matches the closed form. All inputs assumed. Stylised.
All 34 Self-replicating manufacturing projects →
Other research topics
Proper scoring & elicitation28Effort & peer prediction9Verification games & slashing19Detection & tolerances14Markets as routers13Prediction-market design9Paying contributors8Decentralised training systems23Digital twins & sim-to-real164LLM chip design loops40Robot manufacturing loops53Ambient AI assistant46Self-replicating manufacturing34Simulation-first design64Engineered clothing45Task-specific AI accelerators40Algorithmic chip-design loops42Open-source purpose-built robots44The software-engineering loop43Adversarial human imitation41Open-source residential construction41Autonomous multi-angle capture34Sensing, imaging and 3D31Energy supply and dense energy storage39Robot societies among people31Agentic co-design of low-cost robots27Laundry-hanging robots25Machine learning on qualitative data23Robots on the building site27Civilizations & group psychology1History & human sciences1
Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.