Cutting round hole in corrugated iron clad garage.

I need to run a pipe 68mm diamater or possibly 110mm through the wall of my garage. The wall is timber clad with corrugated iron. The founds of the wall are concrete and the corrguated iron is at least 2ft into the ground so I've decided to go through the walll above ground rather than under it. The garage is old and the corrugated iron seems thick.
Can anyone suggest a method of making a hole?
My thoughts were
1. Jigsaw, but no real way of holding corrugated iron to wooden wall of garage so it will vibrate like hell.
2. Drilling a series of small holes round the edge of the 68mm hole and doing a join the dots with a pair of tinsnips.
3. Cutting the 68mm hole from the inside and removing the wood . Drilling the centre of the iron, snipping several cuts to the edge of the 68mm hole and trying to fold the iron back into the garage.
4. Cutting the hole with a pad saw with a metal blade.
I suspect once ive started with any method I'll have to carry on, so want to be sure what I'm doing before I start.
Thank
Ian
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On Wed, 24 Oct 2007 18:00:14 -0700, ian wrote:

=================================If you have an arc welder you can use it to burn a hole by using excess current with thick rods - say 1/8". The edges of the hole won't be very neat and of course the method does depend on having an arc welder in the first place.
An alternative method would be to buy or hire a 'nibbler' which will cut corrugated if used carefully. This again depends on the thickness of the corrugated as any nibbler has a limited capacity.
Cic.
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On Wed, 24 Oct 2007 18:00:14 -0700, ian wrote:

holesaw?
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John Stumbles

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Unless there is a compelling reason to do otherwise, it would be very much easier to cut a square aperture in the corrugated iron (using an angle grinder), then fit a collar around the pipe.
If you wanted to be fancy you could use an angle grinder to cut a closer-fitting hexagon or octagon.
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