Best tool for cutting roof vent opening?

[mayble]

What's your tool of choice for cutting out the opening for the roof vent?

Dremel?  Jigsaw?  Other?

I own zero tools, so I'll have to rent/borrow something to work with.  I'd much rather cut from the inside, if that makes a difference, because I will be cutting right at the very edge of the roof support and don't want to cut into it. 
What do you all suggest?

 

[highdesertranger]

the easiest tool is a sheet metal shear. gives you a nice clean edge and not a bunch of metal shavings to deal with. a lot of people use a sabre saw(jig saw) the only problem with that is the large amount of metal chips. on a side note if you do it from the inside watch your eyes. gravity is your enemy here. if you do it from the outside you can rig a box or bag under the cut to catch the shavings. also you can mark where you want the cut and drill a hole at each corner then do the cutting from above. highdesertranger

 

[Putts]

 I'd much rather cut from the inside, if that makes a difference, because I will be cutting right at the very edge of the roof support and don't want to cut into it. 
What do you all suggest?

I use a jig saw. I mark it from the inside and then drill small holes right at the corners. Then re-draw the hole from the outside to match the holes. Then cut from the outside so I don't have to have all the shavings fall on my head. Also, the partial hole left at the corner prevents stress from building up at 90 degree corner and tend to prevent cracks propagating from the sharp edge.  Kinda like this.

An engineering table someone turned me on to said the hole should be the same radius as the thickness of the metal. So drill size should be 2x the thickness of the metal. 1/16" metal = 1/8" drill size.

 

[Almost There]

You want the drill hole size to be big enough to get the saw blade through...much larger than 1/8".

 

[Putts]

You want the drill hole size to be big enough to get the saw blade through...much larger than 1/8".

You can drill a larger hole for the saw blade within the part being cut out and work your way up to the lines.  Sorry, I should have mentioned that the holes weren't for starting the saw, just for marking and stress relief.

 

[Trebor English]

I used a jig saw.  I used 6 or 8 rectangular magnets to catch the sawdust.  That left some of the sawdust slightly magnetized making cleanup a little more tricky.  It worked well.

 

[caretaker]

just a suggestion, make as much of the cuts outside that you can, what ever tool you use will be awkward to use on your back/ over head. bet you ultimately use a jig saw.

 

[MikeRuth]

Did mine with a jig saw from the top after drilling pilot holes in each corner. One larger hole next to the edge line large enough to drop the saw blade in. Used a metal saw blade. Was done in just a couple minutes. Cleanup took longer LOL,

Oh and I put down Blue painters tape on the roof top along the cutting line to prevent the saw base plate from scratching the paint.

 

[WalkaboutTed]

For the a fantastic vent, Hubby drilled the corners and then used an angle grinder. Same thing for back door windows. Having never done anything like that before (read: petrified to cut gaping holes in brand new vehicle), he went to a junk yard and bought am old steel hood and practiced on that.
Ted

 

[MrNoodly]

And angle grinder is easy and fast — cuts like butter — with no need to drill any holes first.

 

[Weight]

I use an air chisel with a bit called 'claw ripper' https://www.grainger.com/product/WE...m/rp/s/is/image/Grainger/4MHE7_AS02?$smthumb$

 

[Queen]

I use an air chisel with a bit called 'claw ripper' https://www.grainger.com/product/WE...m/rp/s/is/image/Grainger/4MHE7_AS02?$smthumb$

Used that to cut cars apart when I was a firefighter, took sheetmetal apart like butter.  Although in that job no care was given to clean neat cuts.

 

[highdesertranger]

yes an angle grinder works, but it makes a hell of a mess and sparks. the debris from the cut is extremely hot and it will burn into paint and plastic. plus it melts the paint back from the cut leaving bare metal to rust. I just wanted to post that for anybody who doesn't know this. highdesertranger

 

[Putts]

^^In addition, my vehicle has an aluminum body and the aluminum will pack into the grinding wheel. Probably not a problem for the OP, but worth noting if your body is aluminum. Metal jig saw blades will also pack and overheat if the teeth are too small or you push too hard; the overheated blade packs faster. A medium toothed metal blade and slow cutting speeds helps, but you may still need to unpack the blade with a wire brush, or better yet, a file card. (A device with short metal bristles for cleaning packed residue from files.

 

[olddude48]

Jig saw. Open up a garbage bag, tape it to the inside of your roof around the outside of your cuts. It will catch the metal shavings.

 

[John61CT]

Surprised no one mentioned the higher speed RotoZips, like a Dremel on steroids.

With the metal Xbit and circle jig, can cut perfect circles in up to 18 gauge steel.

For straight cuts, there's a 90° adapter and metal ZipWheel, turns it into an angle grinder.

Very flexible tool, attachments for masonry, wood, even diamond ones for tile & ceramics, easy to make a little BBQ from an old flowerpot, just carry the grate!

Often go for peanuts on fleabay.

 

[Willy]

I'd use (and have used) an angle grinder, as others have mentioned. I've also used a jigsaw but, instead of jigsaw blades (which wore out quickly), I used cut down sections of hacksaw blades. ..Willy.

 

[jonyjoe303]

cordless jigsaw from harbor freight (30 dollars) with battery, just don't leave charging more than 3 hours, it doesn't have a smart charger. Used it for cutting roof vents, holes on the side of my van, and also to cut wood panels for inside my van. It's a good investment.

Yes I recommend you check the inside of the roof first, make sure there's no wires, or support beams in the way, with the headliner you might not be able to see them.  But do the actual cut from the roof, for better accuracy.

 

[galladanb]

I used my 40 year old jig saw with a metal blade using fine teeth?

Cuts like butter, made a lottttttttt of noise. The neighbor's even dropped by to see what was going on, lol!!!

Such Fun!

 

[jonsun]

Did I seriously get to page three and not see a sawzall? it literally saws all peeps