Making square holes in thick Aluminum Plate

Gentlemen, Hope you are fine wherever you may be.

I have a job which came my way which calls for making 2"x2" square holes in 3/4 inch aluminum plate. I am a construction worker, carpenter, with access to a heavy mill-drill machine and a small home shop size band saw. I have to make

24 of these square holes in separate 5" x 6" x 3/4" sections. The tolerances are not tight. + or - .01 inches is ok.

My question is what is the best way to do this? From what I can see there are three choices.

  1. Layout the square, drill a 5/8 hole, put a hacksaw blade through and start hacking away. Finish off using an end mill. Of course I might need a new set of arms when I'm done. i need a new brain already!

  1. Due the same but weld the bandsaw blade through each plate and cut using the band saw before finishing with the mill.

  2. Drill out a square shape formed by a series of holes using a 1/4" drill bit and finishing with the mill.

My 3 ideas might suggest to you that I have little experience with machining metal. And that would be quite true. So I would appreciate your suggestions.

Thanks, Rich

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I've heard it said that machining aluminum is like machining wood.

Ok, that's not entirely accurate, but...

I'd be inclined to cram a roughing endmill through there and take it all out in one pass, letting the slug drop through. I'd do the same with 3/4" tool steel given a capable machine. While you won't need a hacksaw, your arms will probably be pretty tired by the end of the run.

How large of an internal radius (in the corners) can the application tolerate? Obviously, the larger the rad, the larger the cutter, the heavier the cut. You'll want less flutes as opposed to more flutes (for chip clearance). LOTS of coolant. Your table will probably be overflowing by the time you've finished a couple of pieces.

If your machine has a DRO, you'll have an easy time. If not, I'd be inclined to set up a bunch of indicators or stops to make the job go quickly. 24pcs is enough to justify a longer setup, IMHO.

Good luck and don't forget the coolant!



Reply to
Robin S.


Suggest dont confuse him further, looks to me he may already be already in deep trouble here as it is.

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If it was just one hole you could do it any way that came to hand. For 24 holes in 3/4" plate you could be there for a couple of days with the wrong method. Ideally it wants a laser cutting machine which would slice them out in a few minutes. You might be better off finding someone who can do that and adding a markup.

If you have to mill it out then I'd suggest a smallish 2 flute milling cutter and do it in maybe 2 passes each 3/8" deep. Forget sawing. You'll still have to clean up the edges and the sawing won't actually save you much milling time.

Reply to
Dave Baker

You may want to make a template, then use (since you are a woodworker) a hefty router with the proper bit (carbide tipped) and run the router around the inside of the template, increasing depth over 3 or 4 passes. A router *will* cut the aluminum and 3/4 depth isn't all that much. HTH Ken

Reply to
Ken Sterling

How about finding someone with a large broaching machine? If you drilled the holes first it might not be all that expensive.


Reply to
Leon Heller (njrich) wrote in news:

Find the closest shop near you with an abrasive jet machine and send them to him. Abrasive jet can do this in a very short amount of time, at a very, very reasonable cost.

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If you start with a pilot hole you can use a down spiral roughing bit that will shove the swarf out the bottom, MUCH easier to see what is going on.

But some>>Gentlemen,

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Use a hole saw that is 2" diameter. 1. Lay out the holes. 2.Drill small holes in the corners, maybe 1/16" diameter or smaller. 3. Drill out the 2" hole.

  1. Finish by removing the remaining stock (not much) with an approriate milling cutter. File corners if you need to. I had to do this for 14 holes of 3 different sizes (3/4", 7/8" and
1") in 1" thick steel plate once. I used this process, but the dimensions had to be closer. So I used my shaper with a square, relieved on all four sides cutter to remove all the remaining material. Pete Stanaitis


njrich wrote:

Reply to
Pete & sheri

Hi- you could waste most of the stock with a good hand held saber saw with a coarse blade with lots of set. If its tough going, cut a series of holes around the perimiter, say 1/4 inch dia. on 3/8 centers before using the saber saw. Finish with a file like bump and paint guys use on lead- or a 1" wide vertical belt sander designed for internal sanding- or with a single pass in the vertical milling machine, or some combo of these. I would layout the holes with layout dye and prick punch along the lines in case the line gets "lost". Be aware that alum. can be tricky to drill-flatten the cutting edge a little on a stone. Consider clamping two or more plates together to save time. Consider bandsawing out the hole without breaking the blade and then welding the slot closed. Perhaps the saw slot could be left as is; no way for me to tell. I think my

24'' Delta floor mounted scroll saw could cut the aluminum with one starting hole. I think you will find trying to cut multiple depth cuts with an end mill more trouble than it is worth. Regards, jim
Reply to
Jim L.

I like #3:

Mill to tolerance. Don't forget to ask the designer / customer if you can drill

1/4 holes directly *on* the corners so there's no inside mill radius. Getting a yes on that will save you hundreds in labor, so lean on it. Don't take no for an answer unless it's a work of art, and you have to file out those corners square for appearance.

If it's functional, 1/4 holes in the corners just show that you are thinking, not wasting someone else's money. With a tolerance of

anyway, losing 1/8 inch out of the corner of a 2 inch square hole is a quibble.

You can finish 3/4 inch plate with a 1/4 inch long end mill, barely, but to hog, use 1/2 inch.

Consider locking the spindle somehow ( Does your belt need replacing anyway? Nail a plywood board between the belt legs) and using a carpenter's mortising chisel to square the corners, with the ram stroke on the mill, and feed of

0.005 diagonally, that is 0.004 on x and y should do, per stroke. Maybe a little less near the corner, to finish. Feel for the feed, use judgment.

Square the chisel to the table by clamping a bit of tool steel to it.

Or send it out to be water jet cut NC. Fast, easy program to write. More than one part, so programming amortizes.

I tolerance everything and tolerate everyone. I love: Dona, Jeff, Kim, Kimmie, Mom, Neelix, Tasha, and Teri, alphabetically. I drive: A double-step Thunderbolt with 657% range. I fight terrorism by: Using less gasoline.

Reply to
Doug Goncz

To find waterjet / abrasivejet shops, visit:

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- Carl

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I do not have my catalog handy, do those drill bits (Watts drills) for square holes go as large as 2"?

-- wf.

Ken Sterl>

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