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Cutting a 4 inch hole in steel sheet

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Cutting a 4 inch hole in steel sheet

Postby the bear » 17 Feb 2022, 17:19

I need to cut a four inch hole in the steel lid of a barrel. I’m guessing that the steel is about 1.5mm thick but happy to be corrected if they are a standard thickness. I’d like to do a neat job not just hack at it.
Options considered are jigsaw but I dread to think how many blades I’d get through of how neat it would be. I could drill a series of holes around the circumference then jigsaw between. I could try the small angle grinder at an angle but think this would be difficult to control. I doubt any would be particularly neat and all require significant time with a file to neaten up. If there a way of drilling a 4 inch hole with some sort of core bit or hole saw. Needs to not cost a fortune for one hole

What’s my best option?

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Re: Cutting a 4 inch hole in steel sheet

Postby AndyT » 17 Feb 2022, 17:57

If I was doing that, I'd try a tank cutter in a brace. If you search eBay for "vintage tank cutter" you'll see the tool I mean. They are pretty common and cheap. They were made for cutting big holes in galvanized steel water tanks in lofts.
A central drill makes a central pivot for a hard, sharp cutter which shaves the metal off a little at a time.
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Re: Cutting a 4 inch hole in steel sheet

Postby the bear » 17 Feb 2022, 18:45

Thanks Andy. Never heard of them but as you say quite cheap on ebay. How quick are they, how long should I expect this to take me? Are the cutters easily sharpened in case I get delivered a blunt one? Just then need to find a brace to put it in, my dad has one but lives 180 miles away. I like this idea if it works

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Re: Cutting a 4 inch hole in steel sheet

Postby Trevanion » 17 Feb 2022, 19:03

A decent hole saw that isn't made from cheese in that size will cost you about £15, then you need an arbour which is another £5-10.

Andy's suggestion of a tank cutter is worth a punt, you can get them to fit in a cordless drill but I imagine one to cut a 4" hole might be expensive.

With what you've already got to hand a good jigsaw blade like a Bosch or Starrett should manage it with ease though in that thickness, I would expect several holes from one blade, drill one hole and cut all around.
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Re: Cutting a 4 inch hole in steel sheet

Postby Doug » 17 Feb 2022, 19:06

Just done exactly this on my cyclone build, I needed to cut just over a 5” hole in the barrel lid I did it with a metal cutting blade in my old dads jigsaw & it cut through it like butter, done in seconds.

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Re: Cutting a 4 inch hole in steel sheet

Postby spb » 17 Feb 2022, 19:07

Depending how much you want to get it done versus enjoy doing it, I'd be looking at either Andy's suggestion or one of these. If you don't have the arbor already it's another fiver.
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Re: Cutting a 4 inch hole in steel sheet

Postby AndyT » 17 Feb 2022, 19:29

the bear wrote:Thanks Andy. Never heard of them but as you say quite cheap on ebay. How quick are they, how long should I expect this to take me? Are the cutters easily sharpened in case I get delivered a blunt one? Just then need to find a brace to put it in, my dad has one but lives 180 miles away. I like this idea if it works

Mark


No direct experience of using one on steel I'm afraid - but they clearly worked 50 years ago and I don't think there's any special complication with sharpening etc.

Doug's jigsaw looks good!
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Re: Cutting a 4 inch hole in steel sheet

Postby Dalboy » 17 Feb 2022, 19:36

Other than buying anything if you have a jig saw cut inside the line of the hole and bring to final size with a file may take a while but at least it should be a clean hole
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Re: Cutting a 4 inch hole in steel sheet

Postby the bear » 17 Feb 2022, 19:41

Thanks all.
Don't have much metal working experience hence the question. I have a hole saw arbour but would need to buy the cutter, wasn't sure how well they cut metal. Having seen Dougs effort I think I'll just go for the jigsaw now, much neater than I expected.

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Re: Cutting a 4 inch hole in steel sheet

Postby DaveL » 17 Feb 2022, 20:48

I found a 4 inch pipe on the bottom of my cyclone would clog with the shaving from the thicknesser, I reworked mine to a 6 inch pipe as I could not find the knob to turn up gravity.
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Re: Cutting a 4 inch hole in steel sheet

Postby RogerS » 17 Feb 2022, 22:16

Can you buy shaped charges on eBay, I wonder ? :eusa-think:
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Re: Cutting a 4 inch hole in steel sheet

Postby Robert » 17 Feb 2022, 23:26

As an ex sheet metal worker if I wanted to cut such a hole at home I'd use a metal cutting blade in a jigsaw too, then clean up the hole with a half round file.
Keep some oil handy and put some on the saw blade now and then as you cut. I'd be surprised if the drum lid was more than 0.7mm (22swg) or 0.9mm (20swg) thick and a fine toothed metal blade will cut it quite quickly. Don't push forward too hard as the blade might snag then and cause dents.

I've cut metal with fly cutters too and it can get scary and dangerous which is why a hand brace was suggested as opposed to a power tool. Sounds like hard work to me.

If I was still working I'd do it in about 15 seconds with a plasma cutter :)
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Re: Cutting a 4 inch hole in steel sheet

Postby Sheffield Tony » 18 Feb 2022, 00:09

I tried cutting a big hole with a tool which fitted in the morse taper of the pillar drill, and had a central locating peg and an arm with an adjustable flying cutter. I persevered for a few seconds before deciding I liked having fingers too moch for that game. Used a holesaw instead.
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Re: Cutting a 4 inch hole in steel sheet

Postby Pete Maddex » 28 Feb 2022, 11:00

I have done a 100mm hole in steel with a fly cutter and pillar drill running on the lowest speed.

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Re: Cutting a 4 inch hole in steel sheet

Postby AJB Temple » 28 Feb 2022, 11:20

Jigsaw with metal cutting blade is what I used. Quick, cheap and you could do 20 such holes and still have a usable blade. Will take you next to no time.
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Re: Cutting a 4 inch hole in steel sheet

Postby the bear » 28 Feb 2022, 12:12

I haven’t done this yet as I’m still getting a few other bits together for the project. It my first effort will be the jigsaw I previously mentioned as it won’t cost me anything

Thanks for all the replies

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Re: Cutting a 4 inch hole in steel sheet

Postby Mike G » 28 Feb 2022, 12:44

If you do cut thin steel with a jigsaw, your main issue is holding it down close to the cut so that it doesn't bounce around, especially once you are nearing the end of the cut. I've done it previously by clamping some ply or MDF scraps either side of the steel, and cutting through the lot. You don't need to do this, but you do need to think about holding the sheet down one way or another.

Also, your eyes. Wear goggles, because the fine bits of metal that can fly off the blade are hot.
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