Pcb In Enclosure

Discussion in 'The Projects Forum' started by frenchie29, Dec 20, 2008.

  1. frenchie29

    Thread Starter Active Member

    Nov 28, 2008
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    I finally finished my first project. And it's working [​IMG]

    http://store.qkits.com/moreinfo.cfm/MK105

    No I need to install in in one of those
    http://parts.digikey.co.nz/1/1/37693-box-a...-4-1591cbk.html

    the thing is it won't fit horizontally, the board is too short and too high. What would be another way to install it so it's solid and steady and and removable just in case I need to make some modification on it or for repair?????

    I was thinking of gluing 4 plastic legs and drill the screw holes but that's a bit too much work for what it is.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Maybe you can set the box you have aside for the next project and then go ahead and buy a box better suited to the dimensions of the board. You will also need to purchase some mounting hardware like screws, nuts, and standoffs.

    You have invested a good deal of time in getting the kit built and operating so an investment in a proper sized enclosure is warranted.

    hgmjr
     
  3. frenchie29

    Thread Starter Active Member

    Nov 28, 2008
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    that's the best box I could find for that project The battery goes at the bottom then the PCB then 2 xlrs connectors at the top, one on each side and a rocker switch at the top. The layout is perfect except nothing to rig the PCB.
     
  4. jpanhalt

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    Jan 18, 2008
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    That's a great little box. I use them for a lot of things. But, if the box don't fit, you gotta not quit.

    Why use a box at all? I get shrink wrap for batteries. It's thinner than the stuff used for wire splicing. Shrink wrap it.

    John

    View attachment 6009
     
  5. frenchie29

    Thread Starter Active Member

    Nov 28, 2008
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    That's interesting. I found some rubber feet that I'm gonna glue on the thing is I had to change the type of screws and the head of the screw is a bit larger and touching the casing of the pot. Could that be a problem at all if it's touching?
     
  6. frenchie29

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    Nov 28, 2008
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    Hey jpanhalt how do you drill holes with those boxes? I used a saw hole drill but the plastic melted and bunched up at the edge of the hole.
     
  7. jpanhalt

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    Different plastics cut differently. For example, cutting plexiglas and lexan uses a different technique than for cutting ABS. That said, there are some principles that apply to them all:

    1) Don't use too high a cutting speed. Some plastics do fine with usual or slightly slow metal cutting speeds, like acetal (Delrin) and nylon. But for ABS and most other thermoplastics, slow the cutting speed way down to avoid the melting you observed.

    2) Plastics tend to grab the cutting tool and pull it into the work ("hogging in"). Slow and controlled feeds help, e.g., with a drill press or lathe.

    3) Related to #2, plexiglas (acrylic), lexan (polycarbonate) will tend to crack with normal drills. That can be avoided by "dubbing off" the cutting edge. The normal cutting edge on a drill is an acute angle. To dub it off, you grind the cutting edge to make it flat, i.e., essentially a right angle. The drill then scrapes or shaves the plastic rather than digging into it.

    In brief, on a lathe, I use regular cutting tools with slow speeds. When drilling anything that is hard and cracks easily (e.g., lexan, plexiglas), I use a dubbed bit. For ABS, nylon and similar plastics, I just use a regular bit and slow speed.

    If you are using a hole saw, you have got to use a very slow speed and maybe water as a lubricant.

    If you can't do that, you can use a razor knife (like Xacto) and shave off the melted material before it gets to hard to cut.

    John
     
  8. frenchie29

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    Nov 28, 2008
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    K thanks that kind of sucks I paid $6 for that box It's a very strange material I started with a really small regular drill bit just to mark the spot then went with the hole saw but it was very hard at first and then went right trough like butter. I'm going to the hardware store tomorrow what bit should I asked for? Obviously the hole saw is too aggressive for it and was chewing up the plastic instead of cutting it. I also got the exact same size as the hole I was gonna drill (XLR chassis connector) and the hole is much bigger then the drill bit.
     
  9. jpanhalt

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    How big a hole are you trying to make? Large, two-lip twist drills can be very hard to control in plastic. By large, I mean larger than 3/8" or so. Moreover, ones more than 1/2" can be really expensive, particularly if you dub them off and ruin them for other purposes that way.

    For up to about 3/4" holes, I much prefer the stepped drills. They have only one cutting edge and make nice round holes. They work well in hand tools, and you have great control.

    For larger than that, I would use either a hole saw or fly cutter. The fly cutter must be used in a drill press, and the work must be clamped. If you have not used one before, it may not be a good choice.

    What you described happening sounds like the plastic was flexing under the saw pressure, then once it started to cut, it went right through. You probably just needed some sort of backing board. One approach is to clamp a board that is narrow enough to fit inside the box to your bench or drill press base so that it overhangs the edge. Put the box over it like a cobbler does with a shoe on a form and then drill.

    Your hole saw should work with a slow enough speed. It can be used hand-held as described, and is a lot safer, if you are not experienced with fly cutters. A little water or soapy water might help.

    John
     
  10. frenchie29

    Thread Starter Active Member

    Nov 28, 2008
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    All I have is a hand drill 14v

    Here's what I want to install on the box

    http://www.parts-express.com/pe/showdetl.cfm?Partnumber=092-092

    I used a 1 inch bit but I think I will have to go one size lower (7/8) and if it's too small maybe just use sand paper. With the 1 inch I could see light trough it.

    So you think I should stick with the hole saw?

    I still have the old box I'm gonna practice on it.
     
    Last edited: Dec 21, 2008
  11. jpanhalt

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    Jan 18, 2008
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    If you are in the USA, Harbor Freight has a step drill that is big enough: http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96275

    That would be my first choice. The HF tool will probably work well for plastic. I assume there are equivalent cheap import places in most western countries too.

    I would definitely not use either a conventional twist drill or a fly cutter for that size hole with a hand held drill. Your hole saw may still work with a backing board, very slow, and a coolant.
     
  12. frenchie29

    Thread Starter Active Member

    Nov 28, 2008
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    What about a spade drill bit? I'm in Toronto Canada I'm gonna go to Home depot tomorrow man those boxes are morecomplicated to work with then I taught.
     
  13. jpanhalt

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    Home Depot may have those drills too. It carries a lot of Chinese import stuff. The price may be more than at HF.

    A spade drill or Forstner bit (they are similar) may work in a rigid set-up, like with a drill press and with the box well secured. They would probably work better with a harder plastic like Delrin or Plexiglas than with the softer ABS of the boxes. I considered recommending them before I knew how big the hole needed to be and that you did not have a drill press. With a hand held drill, it is likely one side will break through the surface before the other. It will grab and either damage the box, rip the drill from your hands, or both. You would also need to have a good backing support to the box wall being drilled.

    Step drills have the advantage that most of the circumference is used as a guide, so the bit stays centered and you get a nice round hole in thin material. "Unibit" is the original brand, I think. I have a set, and they are probably my most used drill bits. I use them for almost any hole in thin material that is more than 3/16" and not an odd size. You are generally limited in thickness to the length of the step, but you can do thicker materials by drilling from both sides. Also, if you push just a little into the next step, you remove the burr on the top side and camfer the edge just a little. Since the driving force along the drill axis is quite low, step drills can be used without much backing to the material being drilled. Finally, step drills can be used to enlarge a hole slightly; whereas, spade drills cannot.

    The Chinese bits are of variable quality, so pick one that looks good. It may end up costing about twice what a spade bit costs, but consider it a capital investment. That's what I always told my wife when the cost of tools exceeded the cost of the project materials. I have never regretted it -- getting the right tools that is.

    John
     
    Last edited: Dec 22, 2008
  14. KMoffett

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    Dec 19, 2007
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    I'd use a dull screwdriver and a 5# sledge, before I'd use a spade drill bit to cut holes in a plastic case. :eek:

    Ken
     
  15. frenchie29

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    Nov 28, 2008
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    Last edited: Dec 22, 2008
  16. jpanhalt

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    The bits I have seen are made for 3/8 or 1/4 inch chucks. The largest bit I have only goes to 3/4" hole, and it has a 3/8 shank. How old is your drill? Almost all drills made now have 3/8" chucks.

    If the drill bit has a 1/2" shank, you should probably return it. Trying to retrofit your 14V drill to a 1/2" chuck or turning the shank down would be way expensive.

    As for the ebay options, I agree, it is impossible to judge quality from a picture. However, for drilling only plastic, quality is probably not too important.

    John
     
  17. frenchie29

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    Nov 28, 2008
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    Last edited: Dec 22, 2008
  18. jpanhalt

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    The big one in that group looks like it also has a 1/2" shank, which won't fit your drill.

    John
     
  19. frenchie29

    Thread Starter Active Member

    Nov 28, 2008
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    That's what I was thinking I sen an email to the seller. Too bad harborfreight doesn't ship To Canada. I'm gonna try to find a major hardware store since that seems a really hard thing to find here.
     
  20. jpanhalt

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    This seller will ship and specifies the 3/8" shank: http://cgi.ebay.com/NEW-1-4-1-3-8-M...0|66:2|65:12|39:1|240:1318|301:1|293:1|294:50

    It seems the problem is that with diameters >7/8, the Chinese supplier went to a 1/2" shank. Neiko sounds Japanese, which implies higher quality, but it could also just be another name for the Chinese product. That reference is to just the first one I saw. There are most likely others like it. Most seem to be coated with titanium nitride -- I guess people like the golden color. Black oxide will work just as well in your application.

    John

    Edit: You might want to confirm that you need a 1" hole. If 7/8" will do, you will have more choices and can find a bit with smaller increments. The 1/8" increments is relatively course.
     
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