Dumb Novice Questions re Enclosures

Well, I'm approaching the point where I will attempt to construct a circuit in a more permanent form than breadboarding, and have some dumb questions re finding an appropriate enclosure to put it in.

1. The catalogs show about a gazillion boxes in all sorts of materials. If I go with a plastic enclosure, how can I tell whether a particular type of plastic can be drilled (or cut, in the case of panel-mounted components which are rectangular) without shattering to pieces?

2. If I decide to go with a metal box, is it appropriate to tie the circuit ground to the box? I remember when I was growing up back in the middle ages, (tube) circuits were typically built on a metal chassis, which itself was used as the ground. Now that we live in an age where the components are typically mounted on a circuit board, is it still standard practice to tie the circuit ground to a metal enclosure?

Thanks.

Rob Rothman

I used ABS plastic for my project enclosure, and it Dremeled and drilled out nicely.

if you buy a "project box" then you can be pretty sure that you can attack it however you want, except my tip for the day is to use masonry bits when drilling plastic... the low abrasion means that the plastic doesn't usually splinter.

i personally wouldn't use the metal for grounding. if your using low amp / voltage stuff, you rarely have an issue with electrocuting someone, but if you push voltage the wrong way around the circuit you can easily do damage to the circuit.

i guess it will depend on the placement of the project also.

I like Really Useful Boxes for enclosures, plastic is not brittle nice removable lids.
Couple of examples:


Thanks.

Can a UBS or other plastic project box withstand the use of a center punch to mark the positions of holes, or is it necessary to try to hold the drill in the proper position without a center punch dimple? I don't have a drill press, and my experience in drilling metal is that its basically impossible to use a hand-held drill accurately without a center punch mark. I would think that plastic would likely be as least as slippery as metal, and hence would pose the same problem -- or is that not the case?

Rob Rothmen

I have a spring-loaded center punch; I just press firmly tho, that's about all you need.

ABS can take a center punch, just don't hit it too hard. As CrossRoads says, a spring loaded center punch is good, because you can adjust it and it always hits it with the same force.

I don't limit myself to official project boxes. It is important to know that the really clear lids sometimes are rather brittle. But not always, I've built several projects into them.

I build a capacitance meter adapter into a clear plastic box like this:

I would -not- use a center punch on this kind of plastic, though. Using a drill press helps keep the bit from pulling itself in and cracking the plastic, this goes for ABS, too.

Unibit/stepbit also good for drilling plastic, doesn't rip up the plastic or pull thru unexpectedly.

Re: unibit/stepbit, good advice. Lack of a spiral flute keeps it from pulling itself through.

Drilling holes precisely can be tough, even with a drill press. If you have a drill press and you can clamp-down the workpiece that helps too, but it can be tricky to clamp-down a plastic (or metal) box.

Even if you center-punch the hole, the drill can "walk" while you are drilling. A [u]Brad Point Bit[/u] is another type of drill that can help. Brad-point bits are designed for wood. They are OK with plastic as long as the plastic doesn't crack, and they might be OK with thin aluminum, but probably not steel.

See:

Use a hole punch if the front panel is flat and the holes are relatively close to the edges

Also us a nibbler