Cutting a large round hole

As an alternative you could drill a pattern of holes, say 1/2 inch. Air flow is still quite good. If you look at a lot of computer cases you will see they rarely use one large hole, usually a lot of smaller ones, often only 1/4 inch or less.

They do that for safety reason and it does inpeed airflow

It doesn't need to be perfect. I certainly wouldn't buy a big hole saw just for this. I think you could do it with an electric jigsaw with a reasonably fine blade, not too fine or it will clog. For ally spray the work with WD40. Support by sitting the sheet on a partly open workmate so that the blade is going between the flat bits.

Well I bought a big hole saw, will come in handy for other jobs

A tank cutter to me is a hole saw, clamp between wood and preferably on a drill/mill table, dont run to fast and lubricate as you go.

Martin P

Got the hole cutter and done a test

Left hand hole is hole cutter and right hand hole was jigsaw. The left hand hole is much neater

This is the finish which can be flapp wheel cleaned up

However the hole will be covered by this

Quite respectable Petrolhead, i would have expected much worse.
Maybe the grade of aluminium, i always get the cutter deflecting to one side.

Those that intend buying new hole saws the Bosch quick release and arbor are the best, last longer and cut a bit quicker than Starret etc. Have and use both types of Bosch White and Blue for drilling through to 18mm thick in 6082.
I just the hole saw to cut a hole then bore out which brings i back on centre, 18 yesterday and close on 14k holes so far, cant go wrong or i would have changed 25 years ago they work within reason.

So the people who have experience of hole saws were right then?