Enclosure for electronic project - drilling holes

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Hi everyone,

I am in the process of designing a circuit board with a 2 inch speaker. The board will be inserted into a PVC enclosure with a 2" hole in which the speaker will sit behind (The hole in the case will be seen on the front of the unit with the speaker behind it).

I need to make several hundred of these. In my attempts to drill with my drill press, the plastic melts where the bit edges are. :cry:

Is there a way this can be done? I tried a 'hole-saw' bit as well as a wide adjustable bit. Are there "companies" who can do the drilling for me in a professional way? I guess my question is - can my plastic PVC case be reworked to add a 2 inch hole without looking bad so it can be sold in a product?

Thanks for any advice. I am willing to run down to the basement and try some of your tips.

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Milling is the way to go for large holes like 2". Drilling is out of the question for this size, and "hole-saw" *can* be done but you need coolingfluid (mix of oil and water, an emulsion, a white fluid like thick milk)
Years back there was a specialist here that had all sorts of holes "in stock": value 0 as long as it stayed in stock, a few dimes when sold. That was a mindbraker for the bookkeeper, ... as you can imagine :)
For upto 32mm there are special drilling bits that look like a stepped cone: keep speed low and cool the drillbit.

For a small loudspeaker I wouldn't go for one large hole, but for a pattern of smaller ones. Saves a grid in front of the speaker too.

Edit: "emulsion" instead of "dispersion"

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Last Edited: Sun. Sep 18, 2011 - 10:52 AM
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this can be done with conventional tools (hole saw) and cooling fluid is not really necessary. dont try and drill it all at once. turn the speed down on the drill press as slow as it will go an take 'pecks' only removing small amounts of plastic at a time. give a little time between each peck to allow any heat to dissipate. also watch your chips closely for change in texture as this will indicate eating; adjust your peck timing accordingly. you will probably still have to clean up some burrs afterwards manually but if you're careful you should have a respectable looking hole.

hope this helps,
jay

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I used a laser cutting company the last time I needed a quantity of holes done in plastic. Cost me $132 for around a total of 90 holes ... including "translating" my pencil sketch to his cad file.

Ross McKenzie ValuSoft Melbourne Australia

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Here is another vote for laser cutting.

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If you want several hundreds of those enclosures, maybe you could invest on a small mill/router? The smaller ones are relatively cheap, although they do have a limited working area, so you will have to see if they can handle your enclosures.

-Pantelis

Professor of Applied Murphology, University of W.T.F.Justhappened.

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Water-jet cutting can be an alternative to a laser for plastics.

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There are a bunch of folks in the CNCZone.com forum that will bid on small jobs.

What you would do is

1) Draw the shape of the holes in some drawing program
2) Build a quick swap jig for the case you want to hold. This could be on top of a 0.5" piece of plywood, with a few inches on the side so that holddowns can be used.
2) Find a guy nearby that is willing to work with you on CNCZone (a lot of people have the machine needed to do this)
3) He'll import your drawing and convert to a cam file for his CNC machine. This will take about 20 mins.
4) He'll find a way to secure your jig to his machine
5) Offer to stand there and shoot the breeze with him, or even man the jig. You have enough boxes that you and he should be pretty good friends by the time this is done ;)

The key is the drawing and the jig. Have those done and you can save some $.

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You should be able to replace the drill on the drill press stand with a Dremel, and use a cutting tool made for PVC. The reason drill bits melts the plastic is the increased friction on the outside of the drill bit. Mind you you could also use a proper bi-metal holesaw. Use some masking tape to protect the edges from chipping. If it's melting either your blade is dull or you are drilling too fast and not pushing hard enough. Sometimes it helps if you put a scrap piece of wood behind the piece you are drilling for support. A piece of 2x4 fitting tightly inside the closed case should do the trick.

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avrhornet,

Do not run down to your basement. Instead locate a local machine shop that has a manual punch press. The usual brand is "Diacro". Sheet metal fab shops usually have them.

A Diacro punch press takes a wide variety of punch & die sets in many sizes and shapes (I think 2" round may be on the high side of their range.) Ask the shop to sample-punch one of your boxes with the nearest equivalent size punch they have on-hand, to see if you can get a clean hole like you need. I have used them for punching PVC sheet stock which was about 1/8" thick in the past with pretty good results. But the holes were more like 3/4" square. I'd venture that the quality of the resulting hole and edges will depend a lot on the "softness" of the specific PVC the box is made of.

Depending on which face of the box you need to punch there may be some fixturing involved to work within the confines of the punch press's neck, head and die surface.

If this works with the equivalent punch I suggested above, you can buy your own 2" round die & punch set and supply it to the shop that eventually does your punching.

If all goes well, you will probably find that you can punch 3 or 4 boxes per minute once you get everything set-up.

The standard punch & die sets are designed for sheet metal punching. However, the "right" machine shop will know how to modify (grind) the standard punch part of the set to work better with plastic, leather, fibre, etc.

You can educate yourself about Diacro punch presses and punch & die sets on E-Bay. There are always a bunch of all these for sale there. There is one guy in New Jersey that seems to specialize in these. Perhaps he can give you some advice on your particular application.

Also, did you consider punching a pattern of smaller holes in a 2-inch circular pattern, rather than one big hole? Maybe 5,6,7,8 or so 1/2" or 5/8" holes may work just as well. What will protect the speaker cone/diaphram with the 2" hole? An array of smaller holes might perform that function as well.

Also, when drilling various plastics I have found that "brad-point" drill bits work better than the usual twist drills intended for metal.

Brad-point bits look like an ordinary twist drill except they have sharp spurs on the outer diameter of the leading spirals and a sharp centering point as well. They are intended for wood drilling, but work well with phenolic, bakelite, various plastics and even thin aluminum. They come in standard sizes from 1/8" up to 1/2" in local retail outlets, more sizes are available from industrical supply houses like McMaster-Carr. Can't guarantee they will work with your specific PVC, but worth a try.

By the way, when I drill plastics (even with the brad-point drills) that tend to "burn" or "melt" as you are describing, I squirt a little tap water onto the workpiece before I start drilling, then maybe a little as I am drilling. Sometimes this is enough to quell the melting & smoking.

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AVRHornet,

I find building cases to be the hardest part on any project, and I've got no good advice for drilling 2" holes in plastic.

BUT, I do have some advice:

As you work in your shop be sure to wear safety glasses!

JC

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What about a circle cutter, combined with the slowest speed on a drill press?

like this:

By the way, that one is found at: http://www.ptreeusa.com/drill_products.htm
(search for the term "Drill Press Adjustable Circle Cutter" on that page)

Its also available at Harbor Freight, here:
http://www.harborfreight.com/adjustable-circle-cutter-37370.html

You will need to keep the wings sharp, but they are easily sharpened with a hand stone. On the one I have, you can turn the cutters to make either a smooth hole or a smooth disc. What others have mentioned about a backing board hold true here too.

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The circle cutter will melt the plastic. I've used it to make robot wheels, but I have to sand down the edges when it was done cutting.

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Circle cutters and hole saws need to be REALLY slow on a drill press. The real issue is the "surface speed" of the cutting tool. No more than a few mm per second on thermosetting plastics.

Most drill presses will NOT go slow enough!

A good mill, such as a "Bridgeport" will often go slow enough. Then, the hole saw or circle cutter actually becomes easier than most of the other tools.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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I cut all size holes in PVC on my milling machine. I use a very sharp fluted mill and I use air to cool the plastic and clear the chips.

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I agree about slowing down the cutting. I think most people have the drill bit or cutter turning too fast most of the time.

I have to get creative to get the thing turning slow enough for me. I have a drill stand that is powered with a cordless drill and I can control the speed down to 1 rev. per second or so. Instead of using a battery, I made a "plug" out of plywood and brass strips that allows me to power it with my bench power supply.

Much of my drilling is done with a cordless screwdriver with a drill chuck attached, and I've drilled many holes strictly by hand with a pin vise.

I've drilled a few holes in a polycarbonate case with an Irwin Speedbor flat bit. The spurs on the periphery of the bit cuts a very clean hole. It was mounted in the cordless screwdriver turning 1 RPS or slower. The biggest bit is 1.5 inches. Above that I would need to use a hole saw.

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Thank you all for the great tips! I tried garboui's tip of using a hole saw and doing it in several steps. It worked, but like he hinted it is very time consuming so for crank out a lot would be not feasible. I guess the thing to do it to start making some phone calls and sending out emails to some shops. Thank you all again! I will certainly post who I used so if this comes up again, we have some experience.

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avrhornet wrote:
Thank you all for the great tips! I tried garboui's tip of using a hole saw and doing it in several steps. It worked, but like he hinted it is very time consuming so for crank out a lot would be not feasible. I guess the thing to do it to start making some phone calls and sending out emails to some shops. Thank you all again! I will certainly post who I used so if this comes up again, we have some experience.
Adding your location details to your profile will help us provide more geographically relevant answers in future also. Hell, for all I know, you could be around the corner from me and I would suggest that you come to our hacker space where we have a laser cutter about to be commissioned :lol:

Cheers,

Ross

Ross McKenzie ValuSoft Melbourne Australia