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Hand-held case/enclosure design using CAD tools

Discussion in 'Electronic Design' started by Nicholas Kinar, Jun 22, 2009.

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  1. Hello--

    I am working on a custom electronics system which ultimately requires a
    hand-held case design. Consequently, I am wondering if anyone would
    know of a good book, paper or tutorial on electronics case design.

    How would I align the circuit board inside the case with the outside of
    the case? How do I create standoffs for the circuit board? How do I
    effectively deal with the routing of wires inside of the case? Perhaps
    there are more general books that are available on this type of design.
    Does anyone have a suggestion?

    As an aside, I am also curious as to how it might be possible to design
    an enclosure for an electro-optical system. How would I integrate
    lenses and an optical system into the enclosure? Are there standard
    mounting parts for lenses which I can model in a CAD program (and then
    produce using rapid prototyping), or would I simply purchase
    "ready-to-order" mounting parts?

    I've posted something similar on the comp.cad.pro-engineer newsgroup,
    but for this posting on sci.electronics.design, I've widened the net to
    be broader than just using the Pro/Engineer software. I hope that this
    posting should be interesting to a broader group of individuals.

    Are there any resources out there on this type of design? Perhaps this
    is not of interest to those working in electronics (after all, case
    design is sometimes more often done by mechanical and industrial
    engineers), but perhaps there are some "important"
    books/papers/tutorials on how to do this.


    Nicholas
     
  2. I doubt you'll find a book our there on this that really covers what you
    want. It's not really possible, there are an infinite numbers of variations
    possible and every design has it's own unique set of requirements.

    Generally speaking, wiring is not a good thing, and you should try to avoid
    it if possible. A well designed product will for example (if possible) have
    just the PCB with PCB mount connectors that align with holes in the case.
    This is cheaper and more reliable.

    Lens systems are pretty much a custom thing. e.g. look at security passive
    IR sensors and you'll see every design is unique and custom.

    The best way to learn this stuff is to take things apart and see how others
    have done it. Then when it comes time for your own design you can
    incorporate various ideas into your own case.

    Electronics designers who don't for example have good in-house mechnaical
    CAD designers will often resort to off-the-shelf cases for their products,
    and these can have have built in PCB stand-off's, front panel windows,
    battery holders etc. So you pick a suitable case from the countless ones
    available and then design your PCB and product around that case. This isn't
    really suited to very high volume manufacture, but is great for low to
    medium volume production.

    Dave.
     
  3. Thanks for your response, David!

    Ah, I think that you are right. There is a diverse number of products
    out there.

    I've done this once before, but I've found that alignment is sometimes
    really tricky. I suppose that a few revisions of the PCB might be
    necessary sometimes.

    Agreed. I'll take a look at some similar stuff.
    I've done this a few times, and this works really well for most
    circuits. However, if I need to interface to electro-optical or
    electro-mechanical components, the design becomes increasingly
    challenging, especially when the system needs to be ultra-portable. I'm
    either going to have to use a off-the-shelf case, or I will have to look
    into developing my own custom design.

    Thanks, David.
     
  4. Peter,

    Thank you for your reply!


    I suppose that it is best to learn from imitation.


    I agree that parts always need to be on hand when doing the layout.
    I've had a number of interesting experiences when I haven't followed
    this simple design suggestion. The tricky thing with some through-hole
    components is that often the part will appear to fit on the 1:1 scale
    layout, and then it will have to be forcefully pushed on the PCB with a
    pair of pliers. I've broken one or two parts using this method.

    Nicholas
     
  5. This book is pretty good for injection-molded parts:-

    http://www.amazon.com/gp/product/1569901295?ie=UTF8&tag=speffcom-20

    As is this one:

    http://www.amazon.com/gp/product/1569903506?ie=UTF8&tag=speffcom-20

    There are some others-- although a single 6' shelf will hold most of
    the decent books on this subject, IMHO.

    As others have said, look at existing parts and try to visualize how
    the mold opens, how each part gets ejected, and the reason for every
    single detail on the parts. Small differences like inserting a
    deliberate narrow groove where parts fit together (so things don't
    have to line up perfectly) can make the difference between a
    cheap-looking product and a nice-looking one.

    You really have to pay a lot of attention to details such as wall
    thickness, rib height-to-width ratio, material, shrinkage (often
    several percent, and varies with material, additives, process
    conditions etc.), draft (VERY important- just about everything has to
    be slightly angled so it will come out of the mold), and what kind of
    side action is required to do things like make holes on sides.
    One way which doesn't use much material or space is to have part of
    the mounting boss protrude into the PCB mounting hole, but there are
    many, many ways. High volume consumer goods often uses snaps, but they
    have disadvantages.
    A boss, preferably with gussets to strengthen it. Design it for a
    specific type of screw. And put it on the back of the case and/or
    under label so the shrink marks won't show.
    Try to avoid them entirely. Failing that, you can use clips and such
    like. It may be possible to make the kind you need without involving
    side action, particularly if you can cover up a hole to the outside
    with a label or something (eg. another part). A "crossover" (metal
    from mold halves meet to seal off plastic flow) is generally far
    preferable to side action (eg. a hydraulically actuated moving core)
    You can't possibly acquire the design skills that an experienced
    mechanical engineer has, plus industrial design skills, plus specific
    knowledge of plastic part design and manufacturing in just one or two
    books, or just a month or two of study. Knowing a thing or two about
    mold design also helps.
     
  6. Nico Coesel

    Nico Coesel Guest

    Perhaps you can ask these questions as well on a forum about 'solid
    works' (a popular piece of software for designing housings).
     
  7. That's where todays 3D MCAD features of PCB programs like Altum Designer can
    be useful:

    (the good stuff starts about half way through)
    Helps get your PCB/Case design right the first time with more complicated
    projects.
    Many case and part/connector suppliers will provide 3D models on their
    website, so you can just import them and do your clearance/fit checking
    fairly easily. Hammond are one case supplier that provide 3D models for all
    their cases for example.
    Check out an early quick 3D mockup for a new little project I'm working on
    for example:
    http://www.edn.com/blog/980000298/post/1570043757.html
    If you want to do your own cases easily then this mod and their software
    might help:
    http://www.emachineshop.com/
    Their software is easy enough for non mechanical guys like me to start
    producing something useful in 5 minutes.
    Designing your own case that looks good and works well takes skill, time and
    money though, so I'd exhaust all the off-the-shelf cases first before
    resorting to that option.

    Dave.
     
  8. Thanks, David!


    I had a look at the You Tube video, and Altium Designer makes me very
    excited. In the past, I've been using Eagle Cad to do most of my design
    work but it might be time for a change. I'll take a look at Altium and
    see if it will fit my needs.


    I had no idea that you have a blog, David! I think that your project is
    really neat, and I would like to do something similar to what you have
    done with the custom case. I've bookmarked your video blog for further
    reference.


    Which MCAD are you using? Does the MCAD interface with Altium? (I am
    assuming that you are using Altium.) According to the You Tube video,
    there should be a way to exchange data between the two software packages.

    Which manufacturing house is producing your case? What would be the
    cost of manufacturing? I'm currently situated in Canada, but I think
    that most product facilities for plastics closest to where I am located
    are in the United States.


    Once again, thanks David.


    Nicholas


    Yeah,
     

  9. This seems to have been a rite of passage for all those who work in
    electronics. It's part of the engineering experience. Maybe we learn
    something from doing it every time. At least I know that such a process
    helps to drain printer ink cartridges, but oh well...


    Nicholas
     
  10. Great titles! I absolutely love the covers on these books. Although
    there is always a word of warning about "judging a book by its cover," I
    think that these are excellent titles. I'll consider ordering them.


    Ah, neat ideas!

    I'm creating a hand-held ground-based remote sensing system for
    determining the physical properties of environmental materials. This
    requires attaching transducers to the circuit board. The transducers
    that I have been using in previous prototypes unfortunately require the
    use of wires. Clips are a good idea. In my previous circuits, I simply
    left the wires to slop around in the box. This was really not a good
    idea because I soon found that after the circuit was transported,
    vibrations would create a big tangled mess.



    Sigh, I understand the truth in these words. However, because I am a
    researcher working in the context of a university to do research and
    also develop a product, I have a vested interest in also learning about
    new things. Of course, if I was doing this for a company, then it would
    make good sense to hire a mechanical engineer with some experience in
    the field. Moreover, purchasing a few books may provide an enlightening
    experience, and it will simply give me some interesting summer reading!


    Spehro, thank you for this post and for the good book titles. I'll be
    sure to learn a lot during this summer.
     

  11. I'll give SolidWorks a try. Thanks, Nico.
     
  12. Both Solidworks and Altium are $thousands, but if you can afford a
    mold or three, that probably seems quite cheap. ;-)
     
  13. Well, I don't actually use MCAD myself, that's not my area. At work we have
    mech guys who do the 3D models for us, not sure which package they use. But
    if the model is available from the manufacturer then it's easy for me to
    attach this to the component myself.
    Yes, it uses the STEP file format. So if your MCAD package supports STEP
    then you are in business.
    It's an off-the-shelf case from Hamond, I just pulled that 3D model from
    their website. See what I said about the ease of designing products around
    existing cases! They also so custom mods to their cases (cutout/slots etc)
    for a fee.

    Dave.
     

  14. Well, I might be able to request access to a site-licensed SolidWorks
    installation, so it wouldn't hurt perhaps trying it out for a while.

    Concerning the actual production of the case, I may also have access to
    a rapid prototyping machine (there's such a machine in one of our
    engineering lab), so I wouldn't think about trying out a very expensive
    mold until I've learned something about actually working with plastics.


    Thanks, Spehro!
     
  15. Ah, the luxury of having engineers who are competent with mechanical things.

    For years, I've used Eagle CAD. I don't think that this software
    package supports anything remotely related to STEP.


    It would be a good idea to simply pull a model and then change some of
    its aspects. Because I have access to a rapid prototyping machine, this
    might give me an ability to learn from the model and then make my own
    version of it.

    Thanks, David.
     

  16. My remote sensing system will be used in an outdoor environment - so I
    am going to have to ensure that the connectors are waterproofed to
    prevent rain and snow from getting into the case. This was a problem
    with some of my earlier prototypes.

    In the past, I actually used a case from Hammond plastics and created a
    circuit board with holes to fit the stand-offs. I cut holes in the case
    for the USB connector and power jack - but the holes also allowed for
    rain and snow to enter the case. This caused the circuit to
    malfunction. I thought at first that if the circuit is hand-held, there
    should be a good possibility of keeping the circuit dry, but the weather
    thought otherwise. :)


    I don't know if this is a logical idea, but my initial thought was to
    produce an electronics case which also incorporated the transducers. So
    the transducers would fit into a recess at the front of the case, and
    the case would be designed to have a trigger grip.


    I need to also produce a stationary version of the remote sensing
    system. The system will be interfaced to a datalogger and then left out
    in a location which is exposed to the elements.


    I think that perhaps the circuit could be placed into an off-the-shelf
    case, and then the transducers could be placed into a "cradle" designed
    using mechanical CAD software and produced using rapid-prototyping
    technology. Connectors on the outside of the case will be used to
    interface the transducers to the circuit.
    Yes, that is true. I might be able to request access to a site-licensed
    version of SolidWorks, and in addition, there is a rapid-prototyping
    machine in one of our labs. My initial idea was to learn some of the
    basics of how to use SolidWorks and then produce an electronics case on
    the rapid-prototyping machine. I suppose that the more toys you might
    have access to, the more likely it is to get carried away.

    Of course, my first concern is the design and operation of the circuit,
    as it should always be.


    Thanks, Peter.

    :)
     
  17. Nico Coesel

    Nico Coesel Guest

    I your company has such a machine, chances are they have a license for
    Solid Works as well.
     
  18. Yes, they do. It seems that SolidWorks is *always* used with rapid
    prototyping machines.

    Thanks, Nico.
     

  19. Yes, thanks, Bob. All of these program *can* do some mechanical design
    work.


    Nicholas
     
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