What would be the best way to to drill/press/punch a perfect 3/4" inch hole into a big bottle cap?

I would like to put a 3/4" inch hole into a big bottle cap so I can connect a water valve through the cap.  What makes this interesting is that the Cap is very thin metal, and because a valve with a rubber washer is attaching to the cap it needs to be a perfect circle so water wont leak out.  Plus, I would like to be able to mass produce this item (100 an hr), so the method needs to be quick, clean and reliable.

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caarntedd5 years ago
Wad punch and hammer.
bwrussell5 years ago
Get a step drill bit. They are great for drilling round holes through thin materials, especially when the hole is large. A standard drill will tend to make oblong holes, especially at larger sizes. 100/hr leaves you with 36 seconds a unit. That's not much time to grab the cap, clamp/hold, center punch, drill, and set aside. I think with a good set-up and practice you could get 60/hr at good quality but an increase in speed is going to cost money (drill press, punch machine, assistant) and/or decrease quality.
The BEST way would be a small fly-press and a suitable punch and die, and bolster. You can pick up small presses for less than 100 bucks sometimes.

The punch and die set might set you back another 100, new, but shop around.

The clearance between the punch and die is set by the thickness of the metal to be punched - clearly you need a small clearance, for thin metal.
Steve
Burf5 years ago
I don't know what you're planning to make, but I'm nearly certain you aren't going to get a rig capable of turning out 100 units per hour for cheap.
I doubt a regular hand punch will work for you because it will flare and stretch the metal on the backside. A metal stud punch would do but I have only seen them in 7/8 inch or 1-11/32 inch sizes and they run between $250 and $750 U.S.
What I would recommend is a knock out punch, which will produce clean, flat cuts and will set you back $50 to $100 U.S. With a little practice, you could likely turn out 10 to 15 units per hour.
iceng5 years ago
At 100 an hr a manufacturer will make them just 4 U.

Until then a hand punch can do your  task very well.

A