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Author Topic: Drilling holes in sheet metal  (Read 26758 times)
ND9B
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« on: February 14, 2012, 07:25:02 AM »

I need to make some 1/2" holes in an aluminum chassis. I want to make these holes nice and "clean". At work, we would use a giant "Whitney" punch or "Greenlee" knock-outs. But, I don't have access to these tools at home. My experience with regular bits and sheet metal is UGLY holes.

This may sound crazy, but is it possible to use wood "Spade" bits on soft aluminum sheet metal? I have a set of wood spade bits that have "ears" on the ends. They make absolutely perfect holes in wood, thick or thin. Could these bits handle thin aluminum, if used in a drill press at low speed? (I figure it's steel vs aluminum, the steel ought to win.)

ND9B

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WD8AJY
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« Reply #1 on: February 14, 2012, 07:54:47 AM »

I use a UNIBIT (stepped bit) i got mine at LOWES.
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K8GU
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« Reply #2 on: February 14, 2012, 09:03:17 AM »

A step bit works well if you have a drill press and the work will fit in your drill press.  (It sounds like this is the case.)  Otherwise, the knock-out punch is the way to go.  I have 1/2-inch and 5/8-inch Greenlee punches that weren't that expensive.  Is it not possible to bring your project to work or borrow the tools home?  I do this all the time.
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W5FYI
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« Reply #3 on: February 14, 2012, 09:15:33 AM »

FWIW, I bought Harbor Freight's punch set, #91201, and it will probably work on aluminum, but not on anything much harder. Cheaper than Greenlees, at $25, but you get what you pay for. The Unibit in a drill press is probably the better way to go. GL
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K8AXW
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« Reply #4 on: February 14, 2012, 09:44:22 AM »

How many 1/2" holes are you talking about? 

A drill press on the slowest speed and using pilot holes will get your there.  Get a reamer (shaped like a large diamond - not a tapered reamer) to cut the burs on both sides.  Otherwise the only way to make CLEAN holes is with a punch. 

When using a drill press it's essential you anchor your work to prevent "jiggle."  For a chassis of any size, consider bolting a flat 3/4" thick piece of plywood to the drill press stage and then use any juryrigged method of holding the chassis.
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NR4C
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« Reply #5 on: February 14, 2012, 11:50:24 AM »

Yes, a spade bit will work on alum to drilll nice, clean 1/2 inch holes.  Use a drill press, and clamp the work in place.  Go very slowly, but the spade bit will drill the center, and then the 'ears' will sleanly cut the circle out.  Place work on a nice peice of wood as a backing, don't try to cut unsupported.  A bit of light cuting oil on the bit, or workpeice, or kerosene, or even Simoniz wax will make the cuts smooth and nice.


...bill  nr4c
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WB6BYU
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« Reply #6 on: February 14, 2012, 12:12:13 PM »

I've seen plans to modify a spade bit to work better on aluminum.  Basically the portion beside the
center was filed down so that the only cutting surface remaining was about 1/16" to 1/8" at the ends
of the bit.  This then cut a disk out of the metal rather than trying to drill out all the material.
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KK0G
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« Reply #7 on: February 14, 2012, 12:56:47 PM »

Second vote for a Unibit.
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KE3WD
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« Reply #8 on: February 14, 2012, 01:01:28 PM »

Third vote for UNIBIT. 

1/2' HOLE in AL, with variable-speed hand drill, steady hand, no need for a drill press to use one. 

BTW Harbor Freight sells these, but not under the Unibit brand name, look for "stepped drillbit set".  Good price, good quality, at least the set I picked up there a couple years ago is. 


73
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KB1GMX
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« Reply #9 on: February 14, 2012, 02:28:55 PM »

Unibit!  [aka Step drill]

I have three different sizes and have used them for Aluminum, tin plate and
even 1/4" steel plate.

Regardless of the tool and metal, use cooling lubricant (oil, wax), clamp the work
(if it grabs the work spins and knuckles get busted.), use a drill press, and go slow.



Allison
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KB1WSY
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« Reply #10 on: February 14, 2012, 05:50:20 PM »

I have a related question, since I am returning to homebrewing tube equipment after a long gap. What do people recommend for a drill press? It seems that a brand called Dremel is very popular with hobbyists in general, but is that type too "light duty" for drilling aluminum chassis of the kind used for tube equipment?

What about the maximum drill size/chuck on this type of equipment? Can one drill 3/8" holes or does a "normal" drill chuck top out at 1/4"? (That is, without using reamers or stepped bits.) I already have a selection of Greenlee punches for holes 1/2" and up.

73 de Martin (ham callsign pending!)
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K8AXW
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« Reply #11 on: February 14, 2012, 09:34:56 PM »

CHESTNUT:  A drill press gives you more control over drilling than a handdrill.  You can maintain a consistant and constant  pressure of the bit as well as the speed of the bit.  A variable hand drill is OK, but it's extremely difficult to maintain a particular speed.  All in all, the accuracy of the hole drilling can't be replicated by a hand drill.

When I built my HB amplifier I made my own perforated aluminum sheets for the RF cage and power supply box.  I drilled over 6,000 holes with my new drill press.  That's 3,000 pilot holes, with those opened up to the final diameter and then all 3,000 deburred on both sides. 

It took the better part of a week and I had only one screw-up out of all 6,000 cuts.  Try that with a hand drill!   Grin
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G3RZP
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« Reply #12 on: February 15, 2012, 12:52:19 AM »

I just drill them. Pilot hole, drill press, work well clamped, wood backing, ream after if exact size needed, burrs removed with a patent tool, a knife, or even a bigger drill.

I think Dremel are a bit light for that job.

Or use a 7/16 drill and a taper reamer.

Or even a pin cutter - that's an end mill with a locating peg in the middle.
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NO6L
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« Reply #13 on: February 15, 2012, 01:26:50 AM »

And yet there is one everybody missed, hole saws. If you can find them at swap meets, the ones used specifically for metal are the ticket. The ones I have are perfect for tube sockets and SO-239s. You'll find them in sizes far more divers than the ones in home improvement stores. Though they can be handy, they're available from about 1/2" to above 4" at between 1/8 and 1/2 inch increments, depending on size range. "The larger the size, the larger the increments". Yes, they are primarily for wood, but go slow and they do fine in aluminum. The more pricey bi-metal saws can even be used on mild steel.

Do not use abrasive masonry hole saws, they will foul immediately and won't be worth cleaning out.

73
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KK0G
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« Reply #14 on: February 15, 2012, 12:18:16 PM »

I didn't 'miss' holesaws, I just wouldn't even consider using one for drilling a 1/2'' hole in aluminum. A step drill will do the job quicker and easier plus produce a cleaner hole, especially with a hand drill.
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