Design Fundamentals

Patent project is due at final exam period

First: Find out what Ernest Hemingway said about the first draft of anything. It applies to engineering design as well as to writing.

  1. Problem Definition, Scope
  2. COVER YOUR BUTT
    1. DON’T GUESS — KNOW.
    2. Be able to defend any decision you make
    3. Make decision based on the best information
    4. If you don’t KNOW. Tell/ask someone who should.
  3. Get input
    1. First of all, know your job.
      1. learn something about how to do your job better every day
    2. Also, know your industry & company
    3. Marketing
    4. End user
    5. Manufacturing
  4.  Constraints
    1. Cost – will always be a factor
    2. Materials
      1. Know what you can actually BUY.
        1. Shop first, then specify instead of the other way around
      2. Look at catalogs and know what types of things are available
      3. Hardware stores are NOT a good source in general
    3.  Processes
      1. Draft angles
      2. Shrinkage
      3. Wall thicknesses
      4. Minimum bend radii
      5. Tolerance ranges
    4. Environment
      1. Salt spray
      2. Heat and humidity
      3. Ice
      4. Petroleum-based chemicals
      5. Sunlight
      6. etc
    5. Standards/Regulatory
    6. Performance characteristics
  5. Use the tools
    1. Use analytical methods
      1. Understand the limitations of your tool
      2. temper with real-world understanding
        1. e.g., truss analysis is usually 2D
    2. Test your assumptions
    3. CAD
    4. Mock-up
    5. Prototype
  6. Right sized features
    1. Understand tolerance, clearance, allowance, interference
      1. clearance for operation
      2. clearance for access, disassembly, replacement
      3. clearance for tools & tooling
    2. Press-fitting – not always appropriate
    3. Hole Locations
      1. for strength
      2. for access
  7. Rigidity & Robustness by design
    1. DON’T RELY ON WISHFUL THINKING
    2. Properly using friction
    3. Know about 4 Bar linkages
    4. Design joints for the joining method
      1. e.g., don’t glue a butt joint
    5. Fixing on axis
      1. Keys
      2. Splines
      3. Setscrews
      4. Lock collars
      5. Retaining rings
  8. Know your statics
    1. Factors of safety
    2. Balance competing design elements for performance
  9. Know your dynamics
    1. Be careful of binding
    2. Remember efficiencies
      1. Oversize motors
      2. Oversize power transmission elements
  10. Stress risers
    1. Sharp corners
    2. Holes close together
    3. Abrupt changes in cross section
  11. Symmetry
    1. Use symmetry unless there is a good reason not to.
  12. Don’t redesign the wheel – know what you can buy
    1. Know about nominal sizes
    2. Look at catalogs, websites
    3. Don’t assume something is easy to get
  13. Use design guides
  14. Simplify
    1. Standardize, limit types of fasteners, etc.
  15. Proper safety factors
  16. Design for…X
    1. Manufacturing
    2. Assembly
    3. Maintenance
    4. Always consider disassembly!
  17. Robust Design (Taguchi)
    1. De-sensitize to variation
    2. Identify what characteristic are critical to quality (CTQ)
    3. Parallel vs. serial, reliability
  18. Evaluate your own designs, be critical and objective.  What could have you improved on?