I need to make (drill?) several 3/4" holes in 1/4" thick aluminum panels.
I have a 3/8" drill, a 1/2" drill bit, a 4" angle grinder, and hand files. It's a tedious job to drill a 1/2" hole and then use a file to enlarge it to
For example, many electricians have a "Greenleaf (sp?)" punch.. To use it you drill a 1/4" hole, asemle the male and female parts of the punch with thru bold on the 1/4" hold and tighten the bolt. In about 30 seconds you have your hole.
I have had to make holds for "stuff" in the top of stainless steel sinks. Usually, I just used the biggest drill I had (usually 1/2") and then used and "ball" or "cone" shaped grinding wheel to enlarge the hole.
An Al, you might be able to use a reamer.
Or you can use a saw to roughtly enlarge the hole and then "polish" with a grinder wheel as above.
Except for the punch, the results usualy aren't pretty but you usually cover up the hole so who cares.
You can get a set of knock out punches from Harborfreight.com for $15.99. It has 1/2, 3/4, 1 and 1 1/4 sizes punches and dies. Up to 10 gauge steel, aluminum, plastic and fiberglass.
Go to the drill bit section of your local hardware store. They should have hole saws in that size. Not totally precise sizing, but reasonable. Should cost between eight and fifteen bucks.
1/4 inch soft aluminum. I'm sure there are some aerospace grades that might break it. Anyway, a 1/2 inch conduit punch cuts a 7/8 inch hole size. (0.885 inches to be precise) Which is why I didn't post it as a suggestion. A mechanical punch for an exact 3/4 inch hole can be obtained but the price may be very high as opposed to that of a standard widely available conduit punch.
I guess we would need to know if the OP is going to cover the holes before we can say "who cares".
I've drilled many holes that do not get covered up, so I usually care what they look like.
One trick I like to use when drilling metal, especially on a drill press, is to clean up the hole with a bit that is a few sizes bigger than my hole. Slight pressure on the press will clean up the rough edges and impart a slight inward bevel. It looks nice, especially with exposed holes.
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