Newbie - Drilling 1 5/8" & 2" holes in 4" square bar aluminum 6061

I could really use help from the collective experience in the group.
I'm going to attempt to machine some special brackets and would like to
hear any suggestions or alternate approaches. I plan to start with two 4"x4"x8" 6061 aluminum stock bars. I need to drill one 2" diameter hole and one 1 5/8" diameter hole (4" deep through the 8" wide face of the bar). Then I need to drill three sets of holes through the perpendicular face (for bolts). Finally I plan to cut through the center of the block so that I will be left with a front and back bracket to hold two poles (one 2" and one 1 5/8") that are held together with 4 1/2" bolts/nuts.
Does the basic plan sound reasonable (using a drill press)?
Do I need cobalt bits to drill the holes in 6061 aluminum? Or can I use standard metal bits?
Should I use a cutting lubricant? Suggestions?
Any ideas on splitting the block if I don't have access to a band saw?
Do you think the 6061 Aluminum will function as strong brackets?
Thanks very much - any and all comments are greatly appreciated.
Eric snipped-for-privacy@cox.net
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et writes:

No. You'd want to use a boring head in a milling machine, or even chuck the work in a big lathe.
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If you absolutely have to do it on a drill press, then step drill the holes in increments of 1/16" or less esp.as you drill in sizes over 3/4". You'll need a set of S & D drills for sizes greater than 1/2". They have the shanks turned down to 1/2" to fit ordinary drill press chucks. I'm not sure you can get S&D's as large as 2" but however you do it, step drilling is the safe and sane way to go. They make a special cutting fluid for aluminum but kerosene or Liquid Wrench is also good.
Bob Swinney

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It is possible to cut giant holes in 6061T6 on a drill press, but is not much fun.
For a solid 4" thick plate, you will need to cut pilot holes to exhaust the chips, and use a serious hole saw, like the Milwaukee 48-20-5153, a $100 tool.
Drill a guide hole for the centering bit, then drill two or three 1/2" diameter chip exhaust holes that are internally tangent to the cut your are making. These holes must be placed carefully in a symmetric pattern. Make up a simple base plate for your hole saw / drill press and connect to a shop vac so the chips are removed quickly out of the bottom of the cut.
Start the cut carefully, then use WD40 as a lube. Run the saw pretty fast, with a spray can of WD 40 spraying as fast as possible. The cut should take about 30 to 60 seconds on a 1 hp drill press. The metal will get pretty hot, so you need to use as much coolant/lube as you can stand.

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et wrote:

You can do it if you have a REAL drill press. By that, I mean old, American made, and heavy. Like 2 guys can put it in a truck, if they have a forklift. Find a local shop, or well tooled hobbyist, and find out what their favorite beverage is.
michael
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<<<<snip>>>>
Eric,
Whereabouts do you live ???
<G>
--
SVL




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PrecisionMachinisT wrote:

LOL! Thanks...I...needed that.
mj
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1. I would start with some 4x4x4 blocks -- no bandsaw needed then. Besides, unless the bandsaw is a very good and very big one, the cut through the block you plan will be ratty and require subsequent machining.
2. Depends on the tools you have. If you have or have access to a lathe, that's probably the easiest way to do it. Mount the block, centered, in a four-jaw chuck. Drill a pilot hole, and finish up to size with a boring bar.
3. If all you have is a drill press, it better be a big heavy one that can be slowed way down. You also better have a really good drill-press vice, or better yet, clamp the work to the drill press table using appropriate clamps. This task, with inadequate clamping, is a great way to lose fingers or worse.
3a. Step drill it -- takes a fortune in drills, unless you have them already. 3b. Drill out to the biggest size drill you have and then use a fly cutter to widen the hole in steps up to the finish size. Don't be overly surprized if the fly cutter drags the entire chuck out of the drill press spindle -- unless your drill press has a draw bar (rare) it is only guaranteed to keep the chuck in the spindle when the force is straight down. 3c. Chain drill around the periphery of the inside of the desired diameter -- say with a 1/4" or 5/16"bit. a bunch of holes, straight through, almost touching each other. Knock the web out with a chisel and then finish off with the fly-cutter.
4. If you have a milling machine and a boring head, that's the way to go.
5. A word of caution. If you have to ask how to do this job, chances are that either you and/or your available equipment are not up to the task.
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Boris Beizer wrote:

...
AIUI, 4x4x4 should be 2x4x8 since the 2" hole and 1.625" hole apparently are side by side in a 4x8 face of the 4x4x8 block, and the block is to be split on a plane through the axes of the holes. The two 2x4x8 pieces would need to be bolted up pretty tightly (possibly with .01" or so shim between them) before drilling or boring.
If the pole diameter is more than a few thousandths smaller than the drilled-hole diameter, shim around the poles with aluminum or brass foil or sheet.
If the main aim is just to clamp two tubes with respect to each other, it would be much easier, and about as rigid, to use 4 U-bolts and muffler or antenna clamp parts attached to a heavy aluminum or steel plate, instead of a split 4x4x8 block. What size of load will the tube and clamp thing carry? Are the tubes aluminum? Is this outdoors or indoors, overhead or not? -jiw
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Thank's for the clarification. The way you visualized (and explained) the things he wants to make, makes a lot more sense.

Sure, a lot cheaper, a lot faster. I prefer, however, to machine some plugs to fit the ID of the tubes. Say, going in 6" or so on each side. For that matter, how about a sleeve to take up the difference between the OD of the smaller tube and the ID of the bigger. In either case, as you suggested, finish off with muffler clamps.

Can't be a very big load if the tubes are Al.
> Are the tubes aluminum?
If not, there will be inevitable corrosion problems. I'm assuming they are Al because he chose to make an Al coupler.

Sounds like a DIY tent pole.
Boris
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Boris Beizer Ph.D. Seminars and Consulting
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