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  • Golden Rules of Mechanical Design

    Discussion in 'The main mechanical design forum' started by blue_troll, Sep 27, 2011.

    1. blue_troll

      blue_troll New Member

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      I know there are a lot of rules for designing whatever you are designing but is it me or is it that since I did my degree in mechanical Engineering ( 22 years ago ) some of the basic ones have been forgotten or ignored .
      I have worked as a mechanic , ships engineer, field service engineer , project engineer and designer of various items and systems in a team or by myself . So forgive me if I whinge a bit when I say that some rules are definetley not being used

      1. Design everything as though you your self was going to work on it ( or repair it )
      2. Not everything has to have Micro electrickery in it to work . The simplest ideas are some times the most ingenious and reliable .Don't re-invent the wheel.
      3. design for the enviroment it is being used in . If it has to withstand volcano temps chose the materials for this not for polar conditions
      4. If it has to be maintained try to use the philosophy of no tools needed . I put this in because so many machines are so complicated or time consuming to take apart that if you don't make it easy to get at those filters etc then they probably won't get done .
      I really feel good now because although there are probably other rules people could add these are my current and particular favourites that most items I get my way seem to fail on and I have at last put them out there .

      College lecturers please drum it into the younger generation as this seems to be getting worse from my point of view . You could save them some pain when they eventually meet the people they have been designing for :)

      Sorry this is a bit long but when you crack you crack !
       
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    3. GarethW

      GarethW Chief Clicker Staff Member

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      Good thread. We should develop a mechanical design manifesto here!

      My contribution is: Don't be rushed and be thorough. Do not make wild assumptions or leave things to chance if you are unsure. Check, check and check again. If you don't do things properly it's almost guaranteed to cost more time and money in the long run. I've witnessed so many bodged designs by those who do not pay enough attention to detail.
       
    4. Dana

      Dana Well-Known Member

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      If there are two ways to put a part on and one of them is wrong, it will happen. Make it impossible to assembly it incorrectly, which can be as simple as moving one fastener in an otherwise symmetrical pattern.

      Where possible, use several of the same size fasteners rather than several different sized ones, even if some are larger than they need to be.

      Understand, and try to minimize, the manufacturing operations and setups. This includes avoiding machining operations on odd angles where right angles will do, doing as much of the machining as possible from one side, and avoid unnecessary chamfers and such.

      "A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away." -- Antoine de Saint-Exupéry
       
    5. Bill @ ERG

      Bill @ ERG Member

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      I believe that the trend in many higher education institutions to focus on academics has resulted in fewer instructors having adequate practical experience. They can't train new designers to design for the application because they have no field experience or first hand knowledge of the issues in the "real" world. I have heard some educators even talk disparagingly of "applied" design for commercial purposes.

      Some of my rules:
      - if it is a critical component in a critical application, then design it so it does not fail rapidly IE lets you know it needs replacing, but continues to function, even if at lower capacity
      - design critical components so their life exceeds the scheduled maintenance intervals so they don't fail during regular service
      - if it is not possible to design to have adequate life to avoid replacement between service intervals, make them quick and easy to replace
      - keep it simple - add complexity only as necessary to solve problems.
      - be sensitive to customer needs in service, and use materials wisely. Hammers are not better if they are made lighter.
      - be aware of the realities of operator education and experience. Automate functions, or design to make it difficult or impossible for machines to damage themselves through foreseeable gaps in operator knowledge or experience.
      - use good mechanical design first - bad design that functions only through application of complex controls will never function as well, nor be as reliable or durable as an inherently good design with minimal controls
      - avoid designs that require shimming, fitting or critical adjustments - these are likely to be done incorrectly in the heat of the moment in the field
       
    6. AdamW

      AdamW Member

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      Always radius internal corners!

      (or that's where it'll break!)
       
    7. cwarner7_11

      cwarner7_11 Well-Known Member

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      A design is not finished when there is nothing left to add. A design is finished when there is nothing left to remove. This is a paraphrase of a quote from someone else, but I forget where the original came from...
       
    8. AndrewNew

      AndrewNew Well-Known Member

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      Antoine de Saint-Exupéry, as quoted by Dana three posts above yours ;-)
       
    9. samroesch

      samroesch Member

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      I'm actually learning about this right now at school. It's a course called Life Cycle Engineering, and we've been talking about DFMA (Design for Manufacture and Assembly) quite a bit so far. It covers some of what you guys have mentioned about using similar fasteners, making things easy to work on without special tools, easy to disassemble for recycling etc...
       
    10. AdamW

      AdamW Member

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      A few more...

      - Galvanic Corrosion Really Happens (I've seen things that would make your hair curl)
      - Just because you've rendered it doesn't mean it really exists
      - The main purpose of simulation is not to provide answers but to understand the question.
       
    11. ASevern

      ASevern New Member

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      It took a 5 year apprenticeship + more than 5 years at college to get a start in engineering design/production and administration. How do people expect younger generations to get the knowledge in 2/3 years at college/university and hit ground running especially when industry is not doing continuation training. Draughting is a lot easier now with CAD whereas designing is a lot more taxing with the proliferation of changing regulations and standards.
      There is also the problem that lecturers and industry managers are of the younger breed and do not actually understand what the requirements are to provide and employ a fully rounded, able engineering person. You can see that from the job agency website advertisements requiring individuals to be Engineers after 2 years experience.
      In reality Training processes and Industry have lost the plot whilst Government departments have never taken engineering seriously enought to back it with anything more than rhetoric.
      In my work as a contractor I still have to 'mentor' younger engineering personnel through the minefield of providing final products fit for purpose, economically specced, safe to use and documented. The surprise that newbies have in the broad base of information, and activities required, to get engineering projects from start to finish amazes me, frustrates industry and highlights the lack of quality training.
       

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