Expert-level machine design covering shafts, bearings, gears, fasteners, springs, clutches, brakes, and mechanical power transmission systems.
Stress analysis: combined bending, torsion, axial loading. ASME shaft equation: includes stress concentration, fatigue, and combined loading. Deflection: check shaft deflection limits for gear and bearing alignment. Critical speed: rotor dynamics, avoid operating near resonance. Keys and keyways: transmit torque, stress concentration factor required.
Rolling element: ball, roller, tapered roller, needle, angular contact. Life rating: L10 life, 90% of bearings survive to rated life. Dynamic load rating: C value from catalog, P is equivalent dynamic load. Lubrication: grease for sealed bearings, oil for high speed or high temperature. Hydrodynamic journal bearings: oil film supports shaft, no contact at operating speed.
Spur gears: parallel axes, simple manufacture, noisy at high speed. Helical gears: angled teeth, smoother and quieter, thrust force generated. Gear tooth strength: Lewis equation for bending stress at tooth root. Contact stress: Hertz contact, pitting failure mode. Gear ratio: input to output speed ratio, inversely proportional to tooth count.
Bolt preload: clamping force created by tightening, prevents joint separation. Joint diagram: shows bolt and member stiffness, determines load sharing. Fatigue of bolts: preload reduces fatigue load range seen by bolt. Torque-tension relationship: T = K times F times d, K is nut factor.
| Pitfall | Fix |
|---|---|
| Ignoring fatigue for cyclic loads | Static analysis insufficient for repeated loading |
| Wrong bearing selection for combined loads | Use equivalent dynamic load calculation |
| Insufficient bolt preload | Preload must exceed external separating force |
| Gear interference | Check contact ratio and minimum tooth count |