Best way to cut....

[MtB]

I need to cut a 4" diameter hole in the 4mm thick steel roof of our NB. I can think of three ways, none of them entirely satisfactory:

 

1) Use a jigsaw with a metal-cutting blade.

 

2) Chain drill using a 4mm drill then use the jig-saw to cut between the 4mm holes.

 

3) Use a powerful drill and 4" dia metal-cutting hole saw.

 

 

I'm currently favouring 2). Any better ideas, anybody?!

 

Cheers, Mike

Edited April 9, 2009 by mike bryant

[wonderdust]

I need to cut a 4" diameter hole in the 4mm thick steel roof of our NB. I can think of three ways, none of them entirely satisfactory:

 

1) Use a jigsaw with a metal-cutting blade.

 

2) Chain drill using a 4mm drill then use the jig-saw to cut between the 4mm holes.

 

3) Use a powerful drill and 4" dia metal-cutting hole saw.

 

 

I'm currently favouring 2). Any better ideas, anybody?!

 

Cheers, Mike

 

Good quality hole saw, easy, oh use a lubricating fluid as well!

Edited April 9, 2009 by wonderdust

[Keeping Up]

4" is a big hole saw. Personally I'd go for option 1; recently I had to cut a similar size hole, and I had a very old jigsaw. I bought some new blades, and after more than half an hour I'd cut a couple of inches and broken a blade. Then the jigsaw itself broke so I bought I nice new Bosch one. Fifteen minutes and no effort later the hole was complete. I love my new jigsaw!

[Mac49]

I'd go for option 1 too, that's how I did the hole for my stove flue. I used a cheap jigsaw I got from Woolies because it had a 5 year guarantee (not so much use now...) as I thought I might burn it out cutting holes in steel but it's still going strong after cutting quite a few holes in my boat. I used a good quality Bosch blade and set the saw slow using plenty of cutting/drilling paste, was a lot easier than I thought and made a neat hole. However having said that, since then I've borrowed a Dewalt cordless jigsaw and that showed you definately get what you pay for, amazing! (but it was about 20 times dearer than mine!)

Rick

[canalchris]

Done this a couple of times,for chimney flues. I used a couple of worn four and half inch metal cutting discs in angle grinder. finished off with jigsaw .

[colin stone]

Option 1 and 3 are easy - holesaw or jigsaw well oiled are fine and 4mm will be no problem - both will rip though it. Option 2 is a pain in the a**e.

[churchward]

I'd go for option 3 in preference.

[Rick-n-Jo]

May not be "best" way, but this is how I did it.

 

Choose position so as not to hit any frames, wires etc. measure carefully several times , then drill pilot hole.

 

 

I used a Bosch 104mm holesaw and arbor, from Screwfix. Set drill on slowest speed. Use cutting paste, re-applying frequently. Bear in mind that if you are using electronic speed control, ie trigger, rather than a geared low speed high torque drill, then the drill motor (and therefore its fan) will be turning slowly and working hard. I removed the drill/saw from the hole frequently to allow it to cool. You can spin the drill full speed off load to get the fan spinning.

 

 

Now I have to be honest and admit that the above bit of wisdom was only gained after my trusty Bosch drill had died with melted brush holders It was very old, honest! Still, the new 2-speed Makita is great!!

Take it slowly and use plenty of lubrication (as the actress said to.........)

 

Now, I had to do a bit of work with a file, so that I could just fit some 100mm vent ducting.

 

 

This is a snug fit when pushed about half way into a standard mushroom vent.

 

 

Drill and tap holes for the brass screws, and mark and cut off the vent duct flush with the roof lining inside.

 

 

Finish by bedding down on mastic or silicon sealant. Trim the inside with a nice brass grille.

 

Proper Job

 

 

Rick

[Reptile Smile]

^^ Rick FTW

[ditchcrawler]

4" is a big hole saw. Personally I'd go for option 1; recently I had to cut a similar size hole, and I had a very old jigsaw. I bought some new blades, and after more than half an hour I'd cut a couple of inches and broken a blade. Then the jigsaw itself broke so I bought I nice new Bosch one. Fifteen minutes and no effort later the hole was complete. I love my new jigsaw!

Thats how I put our mushroom vents and bulls eye in. Put masking tape on the roof round where the hole will be so the shoe doesn't take all the paint off.

I know a boat builder who cut a boat in half with a jigsaw to lengthen it.

[Big Steve]

Jigsaw definitely. Hole saw might break your drill, will cost lots, might break your wrist.

[blueprince]

Thermite, or as the spell checker says termite. Either would be entertaining.

[Martin Kedian]

Hi Mike I have just cut one with a hole saw It took less than 10 miniutes a New hole saw of good quality for a 102 mm size costs £15,00 from B+Q I will post youu mine if you will send it back when your done It does a nice clean job Regards Martin

Edited April 10, 2009 by Martin Kedian

[MtB]

Hi Mike I have just cut one with a hole saw It took less than 10 miniutes a New hole saw of good quality for a 102 mm size costs £15,00 from B+Q I will post youu mine if you will send it back when your done It does a nice clean job Regards Martin

 

 

Hi Martin,

 

Very kind of you to offer that. Thank you! If they are that cheap though I might as well buy one myself from Screwfix rather than put you to the trouble of posting it, being without it for a while then getting it back half worn out. How many holes is a decent 4" hole saw capable of drilling anyway?

 

And by the way, I haven't forgotten I said I'd post some photos here of the pigeon boxes you made and fitted for us. They are painted now and much admired! A mate of mine actually took some photos of them yesterday for me to put them up on here (along with pics of our excellent new trad cratch cover by Karl Assinger). I'll do it as soon as he emails them across to me.

 

Cheers, Mike

[Narrowboat Jimmy]

Rick has got it stop on.

 

Holesaw all the way. I have cut ALOT of holes in metal this way. I would say tho only really do this if you are going to be using a good drill like makita or dewalt. You should get about 10 maybe 15 holes before your holesaw really starts getting blunt.

 

Jimmy