The Elements of Mechanical Design

Preface Part One Elementary Rules of Mechanical Design 1. Create designs that are explicitly simple—keep complexity intrinsic. 2. Keep the functions of a design independent from one another. 3. Use exact constraint when designing structures and mechanisms—never over constrain a design. 3.1 Exact constraint: a description 3.2 Basic Theory of Exact Constraint 3.3 Exact Constraint in Two Dimensions 3.4 Nesting Forces 3.5 Constraint Theory In Practice 3.5.1 Curvature And Surface Matching 3.5.2 Elastic Constraint Design 4. Plan the load path in parts, structures, and assemblies. 5. Triangulate parts and structures to make them stiffer. 6. Avoid bending stresses. Prefer tension and compression. 7. Improve designs with self-help. 8. Manage friction in mechanisms. 8.1 Avoid sliding friction. 8.2 Maximize the length of linearly-guided components. 8.3 Select rotary motion over linear motion. 8.4 Use rolling element bearings whenever possible. 8.5 Use flexures to eliminate friction. Part Two Essentials of Thought and Procedure in Mechanical Design 9. Use three-dimensional solid model layouts to find the best arrangement of parts and assemblies. 10. Invert geometry to reveal new solutions. 11. Build prototypes of everything—but not all at once. 12. Separate strength from stiffness—and stiffness from strength. 13. Never overlook buckling phenomena in parts and structures. 14. Analyze and test for trends and relationships. 15. Identify contingency plans to minimize risks in design. Part Three Some Practical Advice 16. Avoid press fits. 17. Use closed sections or three-dimensional bracing for torsional rigidity. 18. When designing springs, use a low spring rate and a high initial deflection. 19. Minimize and localize the tolerance path in parts and assemblies. 20. Use mechanical amplification to reduce failures. 21. Include lead-ins in assembled designs. 22. Design assemblies to be self-locating, self-fixturing, self-securing, self-aligning, self-adjusting. 23. Use self-assembling symmetry to create a whole from two halves. The Wisdom of Experience Appendix A: Rules for Exact Constraint Design Appendix B: Nesting Force Windows in Exact Constraint Design Appendix C: Design for Assembly Rules Text Notes and References