Yes, reputable custom gear shops can reverse engineer from a worn or broken sample, but be cautious – worn teeth may have altered profiles, and broken parts might hide original design intent. The process involves six stages.
- Stage 1: Inspection of the sample – The manufacturer checks if the gear is usable. Worn teeth with more than 10% material loss or cracks across the root require reconstruction from adjacent unworn sections. Broken gears can be welded (for prototyping) but not for high-stress applications.
- Stage 2: Metrology and data capture – A CMM or optical scanner captures the gear’s geometry (tooth profile, helix, tip diameter, root diameter, and bore). For internal splines, they use a gear tooth vernier or contact probe. The worn profile is mathematically corrected to the theoretical involute – manufacturers use gear design software (KISSsoft, MITCalc) to extrapolate original dimensions based on standard module/diametral pitch and pressure angle (typically 14.5°, 20°, or 25°).
- Stage 3: Material and heat treatment analysis – A small sample (or non-destructive XRF) determines alloy. Microhardness testing reveals case depth and core hardness. If unknown, they recommend a standard substitute like 8620 for case-hardened or 4140 pre-hard.
- Stage 4: Design reconstruction – Engineers create a 3D CAD model with tolerances. They may adjust the profile to modern AGMA standards (e.g., profile shift or tip relief) for improved life.
- Stage 5: Risk assessment and verification – You receive a “reverse engineering report” comparing original (estimated) vs proposed dimensions. A first-article gear is machined and tested in your housing or a functional fixture.
- Stage 6: Final production – Upon approval, they manufacture the batch. Important limitations: Reverse-engineered gears will not have the exact metallurgy or stress history of the original. For safety-critical applications (e.g., helicopter transmissions, crane gears), you must obtain original drawings or perform full finite element analysis (FEA) and dyno testing. Cost is 30–50% higher than drawing-based manufacturing due to engineering time. Lead time adds 2–3 weeks. Always provide any mating gear or housing – center distance tolerance is impossible to derive from a single worn gear alone.