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Metal enclosure

Discussion in 'Electronic Design' started by Steve, Oct 27, 2004.

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  1. Steve

    Steve Guest

    I want to make a metal enclosure for an electronics product. The enclosure
    will be 4" wide, 6" long, 1" high. Up till now I've been using an
    off-the-shelf standard extruded aluminum case. The main cost has been the
    CNC milling of the front and rear panels (they both have a few holes for
    connectors/buttons/LEDs). Plus it is a real pain to assemble, since the
    front panel is glued to the sides in order to avoid screws showing through
    (it's a consumer item). Now I am hopefully going to make them in bigger
    batches (500s or so), I've been looking at other approaches to save money
    and make assembly easier. So far, the alternatives I've thought about are:

    a) Stay with the extruded aluminium and face plates, but use a stick-on
    overlay over the front panel, so I can have screw holes in the panel behind
    it. However, on such a small unit, I am worried that registration between
    overlay and panel (and bubbles?) will make this problematic or at least be
    slow during assembly - the less skill/judgement decisions required during
    assembly, the better ;)

    b) Use a folded aluminium enclosure, one piece for base, front and rear, and
    one piece for top and sides. Although this would get rid of the screws
    needed to hold the box together, I still need some way of attaching a small
    PCB with buttons and LEDs behind the front panel (I'm using foam and glue
    for this at the moment!). I guess I could use blind fasteners for this, but
    maybe that is not the best/cheapest solution.

    c) A mod of (b) that seems to be used for DVD players etc. - folded aluminum
    plus a plastic clip-on front panel to make it look nice. The metal panel
    behind could then have all the screw holes etc. it needed. Not sure if the
    cost of making the plastic panel is feasible for my quantities (500's)

    Can anyone please suggest another approach, or comment on those above.

    Many thanks,
    Steve
     
  2. Steve

    Steve Guest

    That's an amazing idea that I've never come near to thinking of so far. I
    didn't say, but there are also three 7-seg LED digits and some 6x6 tactile
    switches that currently protrude though holes in the front panel, so I don't
    think it is quite suitable, but thanks for such a novel approach (to me
    anyway.)
    That sounds good. I wonder what the results and costs are like when
    contracted out to an assembly house? It's a real question as I have no
    experience with this.

    The use of slides could be a very good one. The extruded aluminium already
    has parallel grooves along the lengths of its sides for horizontal PCB
    mounting, so I'd need some way of attaching the vertical slides to that.
    Otherwise, I don't mind holes drilled in the base of the unit in order to
    attached the vertical PCB in someway, if that is possible.
    Thanks for your ideas, Rob.

    Steve
     
  3. Hi Steve, not sure if this link helps, but the prices seem reasonable
    for CNCing. But I dont think they will machine user supplied parts
    http://www.emachineshop.com/faq/prices.htm




    martin

    Serious error.
    All shortcuts have disappeared.
    Screen. Mind. Both are blank.
     
  4. Tim Wescott

    Tim Wescott Guest

    With those volumes unless you're cutting costs to the bone you should be
    able to justify getting professional help for the packaging. I'd
    consider finding a mechanical engineer who can help you out.

    Alternately you can go to the enclosure manufacturers to do the work:
    just call up the sales staff and say "gee, I'd buy 1000 a year of that
    if only I could figure out how to make it work the way I need".

    Label manufacturers will be similarly eager to help out, and you can get
    polycarbonate labels with embedded switches -- they look really slick
    and (to the best of my knowledge) can be quite reliable.
     
  5. John Larkin

    John Larkin Guest

    What's wrong with letting screws show? Will that keep people from
    buying it?

    John
     
  6. Steve

    Steve Guest

    Afraid it might - since the front panel is only 4" x1", a couple of even
    small screws will show up quite obviously. It's an audio consumer item for
    putting alongside their expensive kit, and so it will help if it looks the
    part too.

    Steve
     
  7. Steve

    Steve Guest

    Thanks Tim. Actually I am going to visit the existing metalworkers to see
    what they think - I'd like some ideas to give them too so any input here
    would be great. I'll give the label manufacturers a try too. It's all very
    knew to me, so thanks again.

    Steve
     
  8. Steve

    Steve Guest

    Hi Martin. Thanks for the link. In fact I just remembered that site a few
    minutes ago! Prices seem ok in volume, and the software is pretty
    straightforward (the audio help files are worth listening to.) I tried to
    create a folded aluminum lid for starters but the s/w refuses to laser cut
    sheet ally despite saying it is compatible with that (I've emailled their
    support).

    Steve
     
  9. I've been talking to http://www.lansing-enclosures lately; it's still
    off-the-shelf extrusions, but they're nicely consumerized, I think. And
    they sent me to an overlay manufacturer, http://www.polycraftinc.com.
    Between those two I think you could probably get what you need at a
    reasonable price.
     
  10. Tim Wescott

    Tim Wescott Guest

    Then use black oxide coated stainless hex socket fasteners -- that
    should be equally at home in an audio equipment rack or the engine bay
    of a race car.

    :)
     
  11. Steve

    Steve Guest

    Many thanks for the links Walter. The Lansing extruded enclosures could be
    good for consumer items as you say. It's an excellent site too for
    explaining the customisations available, fasteners etc. Bit of a shame I'm
    in the UK, but I'll try them anyway (might have contacts here).
     
  12. John Larkin

    John Larkin Guest

    Actually, exposed screws - especially flathead, countersunk, black,
    hex-wrench types - give gear a high-end look.

    John
     
  13. Rich Grise

    Rich Grise Guest

    Button head. :)
     
  14. John Larkin

    John Larkin Guest


    Hey, just who are you calling a button head?

    But seriously, the other cool kind are allen-drive cylindrical cap
    heads recessed in in milled-out holes, black or stainless. Doesn't
    work for sheet metal, of course.

    John
     
  15. Ken Smith

    Ken Smith Guest

    Add a "finish washer"


    If the product has knobs, hide the screw under the knobs skirt, or use the
    controls shaft bushings to mount it.

    Put blind Pem inserts into the front pannel and run a bolt through from
    the back pannel.

    Electron beam weld the front pannel on.
     
  16. John Larkin

    John Larkin Guest

    No, they're tacky.
    Leave the screws in plain sight. They make a statement: This Product
    Is Held Together By Screws.

    John
     
  17. Rob

    Rob Guest

    Steve, just some thoughts.....

    Is using a 'c' shape extrusion with slots for the PCB to run in possible - a
    single sided PCB with 'reverse mounted' leds (via a 2/3/5mm hole in the
    board or use SMD 'flipside' leds so the PCB becomes the 4th side of the
    enclosure. Silk screen the outside face of the PCB. Without knowing the
    application this may or may not be suitable.

    Polycarbonate or whatever decals are easy to apply without bubbles etc - use
    a squirt bottle with some weak soapy water in it and spray the surface prior
    to fitting the label. You can slide the label around to position it and
    remove bubbles, then either by hand or with a roller or squeegee push out
    any excess water.

    For no screws in the front panel - is it possible to mount the PCB off the
    end caps or in 'slides' inside the extrusion. Could you change any of the
    front panel indicators/controls to ones that have mounting threads and use
    these to hold the assembled PCB in place?

    Can ally extrusions be laser cut??????


    regards
    rob
     
  18. Anders F

    Anders F Guest

    I wonder if that's the message Audi wanted to send when they designed (?)
    the TT (and were followed by many others)... ;-)

    /A
     
  19. The heads can be 'semi-decorative', SS hex button-head screws for
    instance. Or hex cap screws for an industrial look.

    Screws under an overlay make servicing a pain. And the manufacturer
    is the #1 servicer, so make things easy on yourself.
     
  20. Steve

    Steve Guest

    Thanks for all the input. I'm finding myself being tempted to go the route
    that all the DVD player/amplifier/VHS recorder manufacturers seem to use -
    folded aluminum case comprising 2 pieces, with a plastic front panel that
    clips on or screws to the aluminum inside. The screws holding the two peices
    of aluminum together are at the sides and the rear, out of the way. The cost
    of the plastic front panel will be the deciding factor if I do go this
    route. Or I could use a milled piece of solid aluminum... ;)

    Steve
     
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