How to make a small clean hole?

A coworker bought a view camera, and while searching for glass wants to take some pinhole pictures. I ran through the formula, and the pinhole
needs to be about .025". I have, somewhere, PCB drill bits in that size range. The material will be brass shim or soda can. My first attempt was going to be taping the Dremel to the quill of the drill press and go for it. Anyone have better ideas for a clean burr free hole?
Kevin Gallimore
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On Sunday, December 2, 2012 1:53:33 PM UTC-8, axolotl wrote:

Get a bit of aluminum foil, fold into a stack with many layers (16 is good). Stab the center of the stack with a pin.
Peel off layers of the stack until the hole size is right.
Mounting the foil, and protecting it, is left as an exercise.
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This is a good method for very small pinholes, but I think the OP wants a relatively large pinhole in sturdier stock.
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On Sun, 02 Dec 2012 15:11:41 -0800, anorton wrote:

I dunno -- the pinhole pictures that I've taken were done in a home-made camera (cardboard with lots of black paint and electrical tape) exposing onto B&W print paper. Pinholes were made with a pin and aluminum foil, and boy I wish I had know the "stack the foil" trick!
For a hand-made pinhole -- even with a pin in tin foil -- the blur spot is going to be roughly the size of the pinhole. The exposure times -- even with real film -- are long. So a small hole is good for crisp pictures, and you're going to have to have the camera firmly mounted during exposure anyway.
If you want better support, make a blank out of the material of choice to fit the camera, drill a 1/4" or so hole in the center, then tape the foil to the blank with electrical tape. That'll give you durability, while still leaving you with a nice tiny hole in the tin foil.
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wrote:

If anybody wants some...I have a small (Grin) supply of drill bits going down to .003"
Gunner
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As an optical engineer, I have actually done this a many times for various reasons. You do not really need the Dremel. Just use the drill press on its highest speed and very light pressure. The drill press should be small enough to control the force very finely. Those small carbide bits break very easily. Certainly if you just tape the dremel to the quill, it would be hard to keep the bit perpendicular which is probably important to keep it from breaking.
I have had good luck clamping the shim stock between two sheets of aluminum with about a 1/8" hole drilled in the top piece for clearance.
Another, much easier, method I have used is to place the shim on a wood backer and press in the point of a compass or divider. I measured the height on the compass point that gave me the diameter I wanted, marked it, and pressed in up to that point. This leaves a rim of deformed metal on the back side which has a slightly smaller I.D., so I turn it over and repeat from the backside. The rim is not usually a problem, but if you want to get rid of that, you can press on the back side with a larger angled cone tip. You can also try removing it by hand-twisting a larger drill bit from the backside.
Another method I have tried to get accurate holes is to open a (old) dial caliper to the appropriate size, lock it, place the shim over the gap between jaws, then press in the compass point until it is wedged in the gap. I am not sure this is better, though, because the rim on the back side tends to get unevenly deformed.
After thinking about this just now, it occured to me that there might be a better procedure I want to try: Start a small hole with a compass point and wood backer. Then, flip the shim over and finish to the final size on the calipers. Enlarging the small hole from the backside will probably spread the rim open rather than push it through onto the calipers where it otherwise would be deformed.
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On Sun, 02 Dec 2012 16:53:33 -0500, axolotl

Mill the hole, don't drill it. You should be able to find an end mill that size fairly easily. I think I have one in the sets I got from Gunner, complete with 1/4"(?) holders.
Otherwise, maybe use a drill press and drill it, flip it over, run a chisel over the burr, flip it and drill; repeat until perfect.
Question: How do these mfgrs -make- bits that small, anyway?
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A 25 mill is a monster pcb mill if you are making high speed stuff.
I used 7 and 10 mill endmills that were typically 2 and one was a 3 cutter. They are carbide and turn fast - 10k or more and must fly cut Copper and fiberglass and epoxy matrix (and other exotic materials).
Small pcb drills are often sold in Dremel kits. They have the large ring on them.
Martin
On 12/2/2012 4:55 PM, Larry Jaques wrote:

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On Sun, 02 Dec 2012 20:41:58 -0600, Martin Eastburn

I have 500 of those drills (at least) if anybody needs any. Im not sure how the numbering system works however.

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    And the color of the ring tells you something about the size.
    I'm not sure how many in the color sequence, but it is enough so you can usually tell two of the same color ring but nearby sizes apart.
    And the ones in kits for dremels (they all have 1/8" shanks) are usually resharps -- I don't know how many times they will have been resharpened but the glass boards even dull the carbide over time, so they do go out to be resharpened, until they get too short for the CNC machine driving them to accept them.
    Enjoy,         DoN.
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On Sun, 02 Dec 2012 14:55:24 -0800, Larry Jaques

Holders???
Sigh...big sigh......
Shrug

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wrote:

OK, they're not collets, so what's the word for them, Mr. Stroke? :/
Sherline calls 'em holders. Google has 680k hits for "mill bit holder". Whaddaya want from a still-a-newb metalworker?
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On Sun, 02 Dec 2012 22:21:31 -0800, Larry Jaques

No idea. I didnt even remember the drill press.
Gunner
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On Sun, 02 Dec 2012 16:53:33 -0500, axolotl

Since you have the drills the easiest method for you, in my opinion, is to clamp the brass shim between two brass sheets at least 1/16" thick and drill through. The goal is a round hole with no burrs and drilling through the same material for both the wanted part and the back up pieces will work well. One way of getting all the thin pieces to stay very close together while drilling is to use some super glue to bond them under pressure. Then use heat (BUT DON'T BREATHE THE FUMES!) to release the part from the backup pieces. Spin the drill as fast as possible. If you have a thick, say 1/8", piece of brass then use that as the bottom piece and don't drill all the way through. This will help prevent drill breakage. So clean the brass pieces, apply super glue, stack the pieces, put a weight on the stack or clamp in a vise, and after the glue has set drill the hole. You might as well drill several holes at a spacing which would allow you to make several apertures in case one gets damaged. Eric
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On 12/2/2012 5:14 PM, snipped-for-privacy@whidbey.com wrote:

Can you do it with a liquid? Drill a bigger hole. Solder in a 0.025" aluminum or stainless wire. The solder won't stick to the wire. Not sure what surface tension will do to the thickness, but would be easy to try.
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One company uses a chemical etching process on very thin metal.
I'ved used hypodermic needles on gaffer's foil, which is just thick blackened aluminum foil.
Other people have had laser drilled holes.
Poking a hole in foil is only as complicated as you want to make it.
pinhole cameras do not produce the best possible image, so trying to acheive the perfect pinhole doesn't make any sense.
Maing the cone will be harder than the hole.
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On 12/2/2012 3:53 PM, axolotl wrote:

Clamp the material between two pieces of metal - .125 aluminum, for instance and drill normally.
Should leave no burr at all.
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On 12/2/2012 3:53 PM, axolotl wrote:

I have a set of oxy/acet tip drills that you would end up turning by hand. I think that drilling the hole and "filing" with a tip cleaner would give a good burr free hole. You would also get a more burr free hole in brass or aluminum if you blunt the lead edge of the drill flutes like this:
http://www.homemodelenginemachinist.com/f26/how-drill-brass-without-drill-grabbing-7914/
look at photos about half way down the page.
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Make a dimple in the shim stock like this ____^____ and carefully file the point until it breaks through, you end up with a hole with extremely thin edges and no burs in a usefully thick metal surround.

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