how to drill a 12cm diameter hole in steel?

[Dave Plowman (News)]

A 120mm Q-Max? Think you'd find it would cost...

[Andy Dingley]

And you'd need an unobtainium Allen key with Arnie Schwarzenegger on the end of it to use it.

[Tony Williams]

It's a spanner operation, but still hard work. There's a (very expensive) hydraulic jack available for the larger Q-Max cutters.

[Dave Plowman (News)]

I've never seen a Q-Max that big, though. Do they exist?

Oh, hydraulic punches of course exist. I'd guess something like that makes the holes in production. But a Q-Max to me is screw operated.

[Tony Williams]

RS 600-082 is 116mm for fans, at only £131-51 each.

RS 605-223 is the matching hydraulic pump kit, at a bargain price of only £417-75.

I've used them to retrofit 118mm fans into steel cabinet doors.

[The Natural Philosopher]

Ther are various ways to make big holes in steel sheet.

One off - drill holes and use file.

Several off, get big Q-max punch or see if someone near has an old set of flypresses and tools.

Production. CNC punch.

[Lenny Brown]

never thought of a treppaning tool low tech but works well

[Kaiser]

Those things are dangerous, unless you are using a pillar drill (drill press) or similar with the job securely clamped or bolted down.

I've seen two accidents using those things, the first a few years ago, was someone with a sheet of metal (that wasn't clamped down properly) spun and sliced the top off his finger. The second was about three weeks ago a guy at the place I was working was using a pistol drill, the fly cutter (trepanning tool) snagged, the drill spun round and broke his thumb.

[Grimly Curmudgeon]

It was somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "John" saying something like:

Ye gods. I remember those - still got them somewhere.

[Tony Williams]

Quite dangerous, more or less guaranteed to snag especially on aluminium. We always run with the belts on the pillar drill not too tight. In that way when it snags the belts slip, rather than the trepanning tool spinning in the chuck (OR, worse still, breaking the taper of the chuck).