Drilling and tapping 200+ 3/8" holes in 3/4" aluminum

I bought a couple of 3/4" thick aluminum fixture plates.
http://igor.chudov.com/tmp/Fixture-Plate.jpg
It was a local sale.
I would like to drill and tap them with 5/16" drill and 3/8" tap, say spaced at 1" interval. That makes for about 200 holes to be drilled and tapped on my CNC mill.
Some questions.
1. What is the best way to drill aluminum with 5/16" drill bit, making through holes. What RPM and feedrate and how often to peck.
2. Do I need to center drill those holes first? It is not really a big deal, just some more G codes.
3. For tapping, can I safely use a ER colleted floating tap holder that has a little bit of vertical internal travel. Like this one:
http://www.maritool.com/p67/ER25-Floating-Tap-Tool-Holder/product_info.html
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On Sun, 26 Sep 2010 16:41:07 -0500, Ignoramus24898

By chance I just finished drill and tap to 3/8 on four holes in AL 1.25" deep. I used G81 (no peck) feed 5.1 speed 2100. Got thick chips that fed out well and broke every two inch or so. Used my coolant mister at a heavy flow.
Karl
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On Sun, 26 Sep 2010 17:34:44 -0500, Karl Townsend

sorry you had two more queries.
I used a solid holder, your floating holder would be nice.
Spot drill if you need to hold +/- .002 location, stub drill maybe +/- .005, regular drill maybe +/- .010 or worse. So how accurate determines answer.
Karl
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I will use a spot drill indeed. Full diameter holes with spot drill, perhaps 1/8" deep, to provide guidance for the regular drill.
i
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On Sun, 26 Sep 2010 21:23:33 -0500, Ignoramus24898 wrote:

Is a "spot drill" the same thing as a "center drill"? (it kind of sounds like it, from Karl's info here.)
Thanks, Rich
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wrote:

No, they are different. A spot drill looks like a drill bit with a special grind point.
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On Mon, 27 Sep 2010 07:12:36 -0500, Karl Townsend wrote:

Ah. Thanks. I sit in an office and fly a desk, while right outside my door are a couple of machinists and weldors - on one side of the shop, we take big pieces of metal and turn them into little pieces of metal, and on the other side, we take small pieces of metal and turn them into big pieces of metal. :-)
On break, the only people I have to talk to, other than the boss and his secretary, are the machinists - When I'm chatting someone up, I like to be able to speak the same language as they. :-)
I do know what "spot-facing" is, however. ;-)
Thanks! Rich
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On Sep 26, 10:23pm, Ignoramus24898

If I were doing this on a manual mill, I would spot drill with a drill whose diameter is about the size of the web of the drill used for the hole.
Dan
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On Mon, 27 Sep 2010 05:06:02 -0700, snipped-for-privacy@krl.org wrote:

Do people use the terms "drill" and "drill bit" almost interchangeably?
To me, the "drill" is the part with the motor, that turns the "bit."
Am I wrong?
Thanks, Rich
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12:58:18 -0700, Rich Grise, snipped-for-privacy@example.net wrote:

As a rule, no. Most people either always use the terms correctly, or always incorrectly. Very few use them interchangeably. ;-)

If you're in a machine shop, you're wrong. If you're in a hardware store, sort of wrong. If you're in a Wal-Mart, well... as long as the guy knows what you mean... ;-)
--
☯☯

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Pretty cool. You feed 5.1 is how many inches per second?
Someone suggested 0.4 IPS, which makes some sense to me.
i
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On Sun, 26 Sep 2010 21:24:40 -0500, Ignoramus24898

That's 5.1 IPM. I just looked at the math, probably could have doubled the feed. Only four holes, chips were feeding, don't fuck with it.
Karl
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Just trying to do the math. 5 IPM, means one 1" hole drilled in 12 seconds, so it amounts to about 20 seconds per hole with rapids and everything. 200 holes, means 4,000 seconds, a little over an hour. Probably can run unsupervised. Not too bad.
How bad were the chips?
i
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I had no trouble with my mystery metal AL. Some AL is a stone bitch to feed the chips up the drill bit, others work great. As nearly all my metal falls in the mystery metal class, i can't tell you which grade is best.
You should feed maybe twice as fast as my small run.
Karl
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Karl, thanks. I will try on some aluminum junk that I have, first.
Tapping, as Richard noted, may be a challenge.
What tap would you recommend for this (tapping aluminum)?
Thanks
i
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wrote:

If they are through holes, I would go with a gun tap - they push the chips ahead of the tap. I have a Procunier tapping head you could borrow for a week or so if that would help. I've tapped a bunch of 0-80 and 4-40 holes with nary a broken tap so 5/16" shouldn't be a problem for that style of head.
Mike
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Mike, did you use that head on a CNC mill?
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wrote:

Not yet, but I know of someone else that has used the same head hundreds of times on a CNC mill.
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I don't agree with Richard's analysis. His method assumes the probabilty of a broken tap is the same on every hole. In fact, once you've set up proper conditions and selected a top quality tap the probablity of breaking goes with wear. Taps used in machines last FAR longer than hand taps.
I use OSG brand taps. Gun flute on thru hole, spiral flute on blind hole. I forget, you aren't set up for rigid tapping??
Both your tension/compression tap holder and the procunier can be set up in your CNC. But, its tricky. You've got to match feeds and speeds to where the tap wants to be.
Karl
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OK, good to hear.

I understand, yes. If I run the spindle at, say, 200-300 RPM, then it would take me about 0.2 seconds to stop the spindle, so about one revolution. The floating tap holder should be able to take care of that. You think ER16 collets would hold a tap well enough?
i
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