Counterboring aluminum using a drill press

This is uncharted territory for me. Done similar stuff with wood using Brad
point and Forstner bits but never with metal. Basically, I need a
counterbore (CB) diameter of about 3/4" to a depth of about 3/8" in 1" thick
6061 aluminum. This is to create a recess for cap screw head and washer
along with room to use a hex socket on the cap screw.
Sourcing the correct CB and pilot seems easy enough except that MMC
recommends HSS ($$) for ferrous and carbide tipped ($$$$) CB for non-ferrous
metals. Surely, HSS should work for aluminum or am I missing something?
Also, what would be the best drill speed to use in a case like this? I
normally use wax lubricant for countersinking metal, is this good enough for
counterboring? Finally, is it advisable to buy say a 1/2" aluminum blank and
practice first or am I making a mountain out of a mole hill?
Reply to
oparr
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HSS will work fine, if your drill press will turn slow enough. For a 3/4" counterbore, you could use a 3/4" end mill, but maybe with a drill press a real counterbore tool is safer. I assume you have a Morse taper to Jacobs taper arbor attaching the drill chuck to the spindle of the drill press? These can come off suddenly when there are side forces or chatter on the tool. You probably want to keep the counterbore well under 1000 RPM for best results.
Jon
Reply to
Jon Elson
HSS works just fine for Aluminum. Thats all my CBs are, and I very occasionally use them on stainless..but its iffy there.
at .75, I go about 120 rpm just to keep the chips under control. I dont worry too much about speeds and feeds with CBs. Too fast is bad.
Finally, is it advisable to buy say a 1/2" aluminum blank and
Always drill a practice hole or turn a practice piece the first time you get a new tool bit, unless you have run them before.
Gunner
"In my humble opinion, the petty carping levied against Bush by the Democrats proves again, it is better to have your eye plucked out by an eagle than to be nibbled to death by ducks." - Norman Liebmann
Reply to
Gunner
I have done this using a carbide Forstner bit with WD40 as a lubricant (slow speed). Not being a metalworker, this is just an every now and again thing. Otherwise, I'd look for more suitable tooling. Kingfish
Reply to
Kingfish
Most counterbores are piloted, so a drill press does just fine. they are sized to fit a socket head cap screw with no washer, so the diameter won't be big enough to fit a socket around a hex cap screw. You may get a deal where there is a choice of OD and pilot to get to where you need to be.
Brian
Reply to
Brian
If you are going to go with the end mill one way to make things a little safer is to:
1. Drill the hole for the "bolt".
2. Drill to almost 3/8 inch with a 3/4 drill.
3. Finish up with a 3/4 end mill to make the bottom flat. Lower the end mill into the hole made by the drill before starting the drill press. A foot switch on the drill press is a great help and lets you have one hand for the quill feed and on hand for the work.
Ray Spinhirne
Reply to
Ray Spinhrne
Thanks all for the advice.
Jon,
I'll use lubrication and clamp the workpiece well to minimize chatter and spin at my lowest available speed (around 600 RPM).
Ray,
I'm a foot switch nut, use it with all rotary tools, can't see how anyone could use a drill press without one. I even use it with a miter saw in case my finger "freezes" on the button in time of danger.
Gunner,
Yeah, I'll buy a 1/2" bar to practice on. Good advice.
Reply to
oparr
||Thanks all for the advice. || ||Jon, || ||I'll use lubrication and clamp the workpiece well to minimize chatter and ||spin at my lowest available speed (around 600 RPM). || ||Ray, || ||I'm a foot switch nut, use it with all rotary tools, can't see how anyone ||could use a drill press without one. I even use it with a miter saw in case ||my finger "freezes" on the button in time of danger.
So how does one find a foot switch, and wire it? Are there OTS switches?
Texas Parts Guy
Reply to
Rex B
Clipper makes them, I bought mine from McMaster Carr. Get the larger one, it scoots around on teh floor less.
For a single phase motor I just wire it in series with the column mounted switch - so I need to have the pedal down and the switch up to get it to run.
My former boss used to call the switch on the column the "anti-suprise-mode switch!"
Jim
Reply to
jim rozen
Got mine at Sears. It has an electrical cord with three prong plug and socket for the drill (or whatever) on the switch body, plug and play, nothing to wire. Note that you basically want an on/off switch, not to be confused with some variable speed foot pedals for sewing machines etc. MMC et al should also carry them.
Reply to
oparr
What about using a flat bottomed drill - one at 90 deg? I only did it once and that was in a 1/4 in. hole with a pilot hole already in place. It was OK for a brass ball valve seat.
Bob Swinney
Reply to
Robert Swinney
If you scrounge around a bit..you generally dont have to "buy" scrap stock.
Guner
"At the core of liberalism is the spoiled child - miserable, as all spoiled children are, unsatisfied, demanding, ill-disciplined, despotic and useless. Liberalism is a philosphy of sniveling brats." -- P.J. O'Rourke
Reply to
Gunner
I have one on one of my drill presses and enclosed it in a plywood box made of 3/4" ply. Helps protect the switch from accidental activation and makes it very hard to move by accident
Gunner
"At the core of liberalism is the spoiled child - miserable, as all spoiled children are, unsatisfied, demanding, ill-disciplined, despotic and useless. Liberalism is a philosphy of sniveling brats." -- P.J. O'Rourke
Reply to
Gunner
Like an endmill? Thats tough because most drill bits have a relatively thin web, which makes them very springy and they tend to walk around. Compare an endmill and a drill bit and you will see the endmill is far far stiffer. Without stiffness, you need a pilot to keep it lined up. Ive cut with some sucess (generally poor) using the spade type wood working bits, but Ive always had to make a small pilot hole to keep it from wandering.
This bit is NOT recommended for any metals.
Gunner
"At the core of liberalism is the spoiled child - miserable, as all spoiled children are, unsatisfied, demanding, ill-disciplined, despotic and useless. Liberalism is a philosphy of sniveling brats." -- P.J. O'Rourke
Reply to
Gunner

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