Re: 3--to-4" dia. holes in steel plate -- how?

J. Clarke wrote:
Bert wrote:


"John" <johnmanders@xxxxxxxxxxxxxxxxx> wrote:


Bert wrote:

I need to put round holes of various sizes (3" to 4" dia.) in steel
plates (1/8" to 1/2"). I don't have a mill or lathe. I could grind or
file the holes to size after roughing out by torch cutting or by
drilling holes around the perimeter, but I'm hoping for a less
labor-intensive method (short of outsourcing it). Specifically, I'm
wondering if there is any tooling suitable for use in a drill press
that could do this job. Can a fly cutter be safely used in a drill
press? And if so, is there such a thing as an adjustable diameter fly
cutter, or are they all fixed diameters? Any other suggestions? (In
case it affects your answer, a couple of these holes need to be
precise enough that another piece can be press-fit into them; the
other holes can tolerate a little slop, maybe +/- 1/32".)

Just for my edification, what would be the tool or technique of choice
for this job in a better-equipped home (non-CNC) machine shop? Mill?
Lathe? Or ??? The plates in this case are in the range of 6"x7" to
8"x10".

One more question in case I decide to outsource this: My material of
choice is hot-rolled steel *with* mill scale (for aesthetic reasons --
it's a sculptural piece where the color and texture of mill scale
would work well). Would this be an unusual request for a machine shop,
i.e., would a typical shop prefer to use cold-rolled and/or pickled
hot-rolled steel?

Thanks.
Bert

Try a rotabroach for the sloppy holes. That will work in a normal drill
press.
Where you need a tight tolerance hole, there's no alternative to
precision machining either the male or female part.
The holes could be made on a mill or lathe equally easily.

John

I checked MSC and McMaster-Carr for rotabroaches. Wow -- they're
pricey. And they don't seem to be available in the right sizes.

But, while looking for these I ran across an "adjustable circle
cutter" (McMaster-Carr item 8830A13). Has anyone tried one of these?
It's basically an arm with a cutter on one end and a guide bit in the
middle. The description says "Use these cutters in a drill press to
cut holes and discs in sheet metal, mild steel, laminates, plastics,
and wood. Unlike hole saws, you can adjust the hole diameter to cut a
variety of hole sizes with just one tool. Maximum safe speed is 500
rpm. Maximum cutting depth is 3/4"." It sounds like it might do the
job, though I have no idea what kind of precision to expect from it.
At less than 20 bucks, it may be worth trying out.


If you're gonna cut steel with one of those things in a drill press then you
need a honking big industrial quality drill press just to swing the thing. Precision won't be good at all, enough for a rough cut or a clearance hole
but if you're going to press in a bearing race you'll have to ream it to
size after cutting. I wouldn't even _think_ about trying to cut anything
heavier than sheet goods with it but I suppose that if you have enough
drill press and enough patience and a good sharpening setup you could get
through what you are trying to get through.

If the bearings are purely for visual effect and don't have to spin or carry
load you might want to get a small plasma cutter, cut the holes a little
oversize, then rather than pressing in the races either weld them or
adhesive bond them (depending on what the aesthetics of the piece allow).

Or just use two sets of races and weld one on each side of the piece, using
them to mask the edge of the actual hole--if you're careful you may be able
to hide the welds behind the races.

A laser job shop can cut accurate, ready to use holes, and that is what I'd do. Plasma? sure, but the holes will not be as clean. A Machine shop could do it too, but I suspect the laser will be cheaper. You need a drawing of the parts and hole locations in DXF format and for minimum cost you might think about letting the laser shop cut all of the pieces of each thickness from a single sheet of HRS.

I would not try cut a 4" hole in HRS on a drill press unless you are masochistic and like to live dangerously.
.

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