MEPX
Chapter 9 of 12All chapters
  1. 1What engineers do
  2. 2The design process
  3. 3Forces and loads
  4. 4Stress, strain and materials
  5. 5Structures
  6. 6Mechanisms
  7. 7Electrical basics
  8. 8Energy in machines
  9. 9Manufacturing and tolerances
  10. 10Safety factors and failure
  11. 11Testing and standards
  12. 12Responsibility

Chapter 9 of 12

Manufacturing and tolerances

Nothing is made exactly to size.

Tolerance

A tolerance states how far a real part may differ from its stated dimension. Tighter tolerances cost more at every stage, so they are specified only where the fit actually matters.

  • Tolerances stack: several parts each at their limit can add up to a gap that does not work.
  • Design so that parts can only be assembled the right way round.

Choosing a process

Machining, casting, moulding, printing and forming each suit different volumes and shapes. The process is a design decision, not something to decide after the drawing is finished.