In article ,
wrote:
Hello again,

[ ... ]

Note that the 12" models can drill holes centered only 6" from
the nearest edge of the workpiece. If this is sufficient, fine.
Otherwise, consider larger, even if you are over your price limit.

The pieces I need to drill now are 1/16" thick (the 1" hole), and 1/8"
thick (smaller holes) and at most 1/2" from an edge, so size is not
an issue.

O.K. If these are not another example of the square tubing
which you mention later on, perhaps one of the heavier examples of the
Roper Whitney hole punches would be faster? I've never used on in
stainless. The smaller size goes up to 5/16" (IIRC) and can (with some
effort) make holes up to 3/16" in 1/8" aluminum. It might take too much
effort for stainless. Robin? You're the one who has done some punch
and die design work recently -- what are the odds of the larger Roper
Whitney handling 1/6" SS with a 1/2" hole? And how long would you
expect the punch and die to last?


... (lots of valuable info deleted )
Note that carbide drills in that size are *very* expensive, so
we'll calculate based on HSS. And I don't think that there are any
Silver & Demming (e.g. reduced shank) drills, in solid carbide, so HSS
is the most likely one for you.

I bought a set of 2 tapered bits, the first one to 1/2" and the second
from 1/2" to 1". These are to drill into 1/16" thick 316 stainless.
They are probably HSS (I don't have them nearby to check at the
moment, they cost $30).

These are the unibit style of bit -- though made under multiple
names by now. They are a nice choice for thin sheet metal, as you have
here. You can (except for the largest size) bring the bit on just a bit
farther, so you deburr the top side of the hole with the edge of the next
step.

The 1/8" 316 stainless will be drilled with smaller cobalt bits.

... (more good info deleted)
How many drill bits do you want to use per hole? Even the 280
RPM one is pushing things a bit for hobby work.

For the 1" holes, the two tapered bits I bought have something like 10
different sizes each, progressively larger. This, I presume, has the
same effect as using 20 progressively bigger drill bits.

In some ways -- yes. It will reduce the maximum torque needed,
as you will only be removing a little bit at a time. However, the
maximum spindle speed allowed is a function only of the diameter of the
hole, as the outer edge is moving faster than anything closer to the
center. Ideally -- you would do better with a variable speed decreasing
the speed as you move up each step -- but this becomes ridiculous fairly
quickly, so a speed set for the maximum diameter will have to do, even
if it is a bit slow with the rest.

Another benefit is that you have only one cutting flute, so the
torque is just that much smaller than the standard drill bit. All of
this makes it easier to supply sufficient pressure to keep it cutting.

Back when we didn't know how thick your workpieces would be, we
had to assume a standard format drill bit, and all the pressure which it
requires to feed. Adding the maximum thickness helps a lot.

You should get a good cutting fluid to keep buildup of metal
from the edge of the tool. And note that the sides of the steps will
rub on the edge of the hole to keep it centered. This might cause some
extra work-hardening at that surface, causing a bit more rapid wear to
the next step.

You may benefit from a TiN (Titanium Nitride) coating (looks
gold) on the step drills to help control metal buildup and supplement
the cutting fluid.

How thick is your stainless steel? You will want a minimum
stroke of probably at least a half inch longer than your workpiece
thickness with a 1" drill. You may need more if you have to lift the
workpiece out of fixturing, or if you need to change the drill bit
without disturbing the workpiece.

This is important, as the 1" holes are to go on opposing faces of 2"
square tube, so if I wanted to drill two holes without unclamping the
piece the stroke should be 2" plus the length of the tapered drill
bit. More than the small drill presses I was considering can do.

O.K. That is a problem -- especially as it can sometimes be
difficult to back one of these drills out which has gone all the way
through a hole. Also -- you'll need to either have two drill-press
vises to support it over the center hole of the table (if any), or to
hold it high enough -- or one larger drill press vise with enough
clearance between the rails for the drill to fully clear as it goes
through.

One thing to consider is that if you go all the way through from
one side, the exit side will have a burr on the outside where it can cut
someone with careless handling. Better if that is kept inside the tube.
(And to clean the burr off, you would need an even bigger countersink
bit than your hole. Maybe one of the countersinks which are a cone with
a hole drilled through at an angle to provide one cutting edge.

The alternative is to unclamp the piece and reverse it, but this
gets into issues of alignment and rigidity, as someone else pointed
out.

Since your total tool length is probably such that the tip, at
least, will start on the other side, this can be used to center the
workpiece after flipping. Hmmm ... 2" square tube? I'm not sure just
how long the working area of the 1" drill is. I only have a 0-1/2" one,
which I find really nice for holes in aluminum chassis materials. I've
never tried it in stainless. All of my stainless is too thick for that
kind of drill to make sense. (I also don't drill holes that large in
the stainless, normally. Biggest is 1/2", with a boring bar in the
lathe to enlarge it to minor thread diameter for 5/8-27 threads.

Anyway -- 2" square tubing is a bit large for a standard twist
drill which would be a good pilot for the Unibit. (Hmm ... again, what
is the smallest step on the 1" ones?) Perhaps a long drill bit of pilot
diameter to go through both sides in one pass, and then use that to
center both sides with the Unibit. This calls for a minimum stroke of
just a bit over 2" -- perhaps 2-1/2" would suffice.

... (more good info deleted)
brands/models. Does anyone have other recommendations?

Yes -- find a used machine tool dealer, and look for a serious
drill press -- with at least a MT-3 spindle. Plan to drive the drills
directly -- no chuck involved.

That's going to be my next step.

Expect that such a drill press will also probably need three
phase, so plan on building a rotary converter -- or hooking up VFD,
which will allow you to get even more speed control, as you can control
the motor speed directly, to supplement the belt reduction.

Nothing is as simple as I expected/hoped, oh well. Still, I recognize
good advice. Thanks!

...
Give us a clue where you are located, and perhaps we can point
you to a used equipment dealer known to do things right in your
vicinity.

Yes! Please! I'm in Red Bank, NJ (central NJ).

O.K. I guess that would suggest Dave Ficken (Mermac tools),
unless he has moved it all to Pa by now), and Dave Sobel. Dave Ficken
is on the web, but you'll probably never find Dave Sobel there.

I find myself reminded of a song by a friend who lives in
Middletown -- "The Long Branch Branch of the Red Bank bank". You might
never have encountered him, unless you are into the traditional music
scene.

Best of luck,
DoN.
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