Cutting holes in roofing sheet

[Chambishi]

I am currently working on a project which requires the use of a hole saw to cut 83mm and 104 mm dia. holes in galvanised corrugated roofing sheet.
I have managed to cut a few 83mm holes but it was hard work as the only hole saw of the correct diameter I can find has a 5 teeth per inch pitch which, when cutting metal of 0.55mm, causes a great deal of snagging. Eventually resulting in three teeth being knocked off the blade.
Any advice would be gratefully accepted.

 

[Silentrunning]

This is just a guess - could you sandwich the metal between 2 pieces of 1/2” or thicker wood? This may help the circular blade remain straighter and prevent any chatter or jumping.

 

[Chambishi]

Update I have managed to successfully cut a number of holes 102mm in dia using a holesaw with 5tpi but only by driving the saw in reverse when on the downward slope of the roofing sheet. The bespoke cutting tool is now in Zambia where it is being used to fit daylight powered lights in very basic living accommodation. If I could supply a holessw with 10tpi it would make life much easier. I can find 102mm 10tpi holesaws in many countries but not the UK. Can anyone help?

 

[Chambishi]

I obviously did not make myself clear. When I said I had used a holesaw I meant that I had cut a hole with a saw designed to cut circular holes which could also be called a hole cutter.
The problem of cutting holes in corrugated roofing material remains due to the relatively coarse nature of the hole saw teeth. It's fine when cutting the top of the roofing sheet profile but when cutting the sloping section the cutter becomes jammed. So I ask again. Does anyone know where I can obtain a 102mm holesaw with fine teeth (10 tpi if possible).

 

[AC Power]

I am not sure if you can even buy a hole saw with a TPI that fine, after all, hole saws are not known to be used for finer work.

I know exactly what your doing. I had to drill hundreds of those hole. Mine were 4" diameter in Q-deck. They were used to permit octagon boxes (and their conduit) to be installed on the top of the roof prior to insulation, tar and gravel. I took a 3' by 3' piece of 3/4" plywood, and made a 4" in the center of it. Then wherever you need to cut a 4" hole in the roofing tin, you place the plywood over the marked location, place the hole saw into the plywood's hole, and begin. Go slow, and hold the drill TIGHT, very TIGHT. And do remember to TAKE THE PILOT BIT OUT. You don't need the pilot bit if you've the plywood to secure any "skating" the hole saw will make upon contact to the tin. TAKE OUT THE PILOT BIT, HOLD THE DRILL TIGHT. As you said, it will feel awful (vibration, snagging, jamming, etc....) when you start cutting the vertical portion of the roofing tin, but that's how I did it.

 

[Chambishi]

I am not sure if you can even buy a hole saw with a TPI that fine, after all, hole saws are not known to be used for finer work.

I know exactly what your doing. I had to drill hundreds of those hole. Mine were 4" diameter in Q-deck. They were used to permit octagon boxes (and their conduit) to be installed on the top of the roof prior to insulation, tar and gravel. I took a 3' by 3' piece of 3/4" plywood, and made a 4" in the center of it. Then wherever you need to cut a 4" hole in the roofing tin, you place the plywood over the marked location, place the hole saw into the plywood's hole, and begin. Go slow, and hold the drill TIGHT, very TIGHT. And do remember to TAKE THE PILOT BIT OUT. You don't need the pilot bit if you've the plywood to secure any "skating" the hole saw will make upon contact to the tin. TAKE OUT THE PILOT BIT, HOLD THE DRILL TIGHT. As you said, it will feel awful (vibration, snagging, jamming, etc....) when you start cutting the vertical portion of the roofing tin, but that's how I did it.

Thanks for taking the time to reply but as I mentioned there is no electric power where these lights are being installed so all cutting has to be done by hand. I have come across 102mm hole saws with 8tpi and even 10tpi but they are only available in Europe, the USA, Australia and New Zealand not the UK The supplier is Eurafco and the saw made by Wilpu.
The website does quote a price in Euro but I am concerned about import tax now that we are not in the UK.
The best solution would be to find a 10tpi hole saw on sale in the UK.

 

[AC Power]

Ok, I must have overlooked your OP comment about being too far from a power source.

With regards a drill, lineman (power transmission) use gas powered drills....maybe you can rent one there.

With regards your hole saw, perhaps a concrete cutting saw (c/w diamond impregnated iron) will work? I know they do cut steel, but I suspect you'd have to keep the cutting cool/lubricated with a squirt bottle of water as you drill. They have NO teeth, and won't snag on anything. Anyways...it's just a thought.

 

[Chambishi]

Again, thanks for your input but Zambia is one of the most impoverished nations in Africa and the thought of giving a diamond encrusted cutting tool to a Zambian who is living in abject poverty would just not work even if it was possible. I'll keep looking for a source of a 10tpi hole saw locally.
Thanks again for your input
Chambishi

 

[Chambishi]

Again, thanks for your input but Zambia is one of the most impoverished nations in Africa and the thought of giving a diamond encrusted cutting tool to a Zambian who is living in abject poverty would just not work even if it was possible. I'll keep looking for a source of a 10tpi hole saw locally.
Thanks again for your input
Chambishi

Thanks for all your inputs but I have engineered a solution using a 10tpi holesaw sourced from Germany incorporated in a bespoke cutting tool. Now it is possible to cut a 96mm hole in a matter of minutes with no snagging.
I have attached a picture of both Mark One and two cutters together with a proof of concept photo showing a bottle installed in a small section of galvanised corrugated steel. And finally a screen shot from a video of a Zambian fitting a bottle light in the roof of a dwelling.