How to cut a 10" round hole in 5mm mild steel?

[Chris Green]

I don't know if the French are into tool hire (the boat is in France), I've never noticed any tool hire places. It's an idea though, I'll hunt around a bit.

[Colin Bignell]

Some Bricomarché stores do tool hire. Also look for "location d'outillage" or "location d'outils.

[Chris Green]

Yes, thanks, I tried "location d'outils" immediately after your original suggestion and there are a couple of possibles locally. I haven't yet really investigated that hard to see if they have anything like plasma cutters.

Strangely there isn't a Bricomarché anywhere near, we have a Leroy-Merlin close and a Brico-Depot not too far away, but that's all.

[Colin Bignell]

My knowledge of diy in France is about 20 years out of date. I can't help with the French for power nibbler either. :-)

[Clive Arthur]

<snip>

A shaped-charge explosive would be quicker. I'd just drill lots of holes then finish up with a grinder, simply because I have a drill and I know it would work.

[nothanks]

Yes, I use an SDS (or dedicated core drill) for core-drilling in walls but this was "just a 16mm bit" ... in other words: lack of engagement of brain and (an expression I'm fond of) hubris leading to nemesis ;-)

[Rob Morley]

Hire a plasma cutter.

[Clive Arthur]

<snip>

True. But it would be done by now.

[Mike Rogers]

Go with the jigsaw. Decent blade and regular drop of oil on the teeth. Mike

[nothanks]

I haven't used plasma cutters but am prepared to believe that they would do the job. However, everyone has a drill and not everyone has access to a plasma cutter (etcetera) and the skills to use it safely and effectively. There are many exotic tools that might make a particular job easier or quicker, but if you ain't got one or don't know how to use it then finding a way to use what you have becomes the better approach.

[Chris Hogg]

Not followed this thread in detail, so apologies if this has already been suggested, but if it were my problem I'd drill a circle of holes just inside the perimeter of where I want the enlarged hole to be, then join them up with a jig saw, and grind away the 'spikes' with a drill grinding wheel.

[Sam Plusnet]

Hmm. 10 inch circle, 5mm steel. How many holes would be needed, and hence how many drill bits would you get through in doing the job? The wear & tear on the drill is another factor.

[nothanks]

Simples! (I think!) 10" diameter is 254mm. Assume a 10mm drill bit so PCD is 244mm and drilling circumference is about 760mm. Assume 2mm gap between holes so about 64 holes needed. So, at 5 mm thickness, that's about a total drilling depth of 320 mm ... not too bad. It may need a couple of drill bits (depending on whether the optimum speeds and oil are used) but wear on a decent drill will be insignificant. I'd guess at about an hour.

[Fredxx]

How are you going to get past the remaining 120mm of steel (64 x 2mm)?

A jig-saw?

And the rest. If going down that route I might start at 3mm before moving to 10mm diameter.

Still think jig-saw is the best route if there's no other method.

[Andy Burns]

Less likely to set the boat on fire than a plasma cutter ...

[Chris Green]

OP here, it has been known! Not with a plasma cutter but....

A few years ago the boat was having an extra steel skin fixed to its hull because corrosion had thinned the original hull. I was inside monitoring things but not quite well enough, some expanded polystyrene (horrible stuff, I've removed just about all of it now) caught fire and I wasn't able to extinguish it immediately. Fortunately the shipyard were

*very* switched on, I got out and there were guys with breathing apparatus and extinguishers there within a minute or so.

It was a bit black and smokey around the area that had caught fire but there was little permananent damage, just some clearing up.

I monitored inside the boat even more carefully while they were welding after that!

[John J]

A gas axe?

[Harry Bloomfield Esq]

Reads from the description, like a 'tank cutter'.

[Colin Bignell]

TNP reminded me of the name fly cutter, but tank cutter seems to be the same thing.

[Sam Plusnet]

Did the same shipyard do the Admiral Kuznetsov? In Murmansk?