I have a vent that I'd like to install in the side of my steel trailer.  The vent requires a 3 inch opening for installation.  Any suggestions on how to create a 3 inch hole in 1/4 inch steel?

It was suggested that I use a cutting torch but I'm afraid it may be catch the inside insulation and paneling on fire.

Thanks.

Round hole?  Or square/rectangle?  If it is round you can get a steel cutting hole saw, if it is straight lines you can get a grinding blade for a skill saw or a metal cutting blade for a reciprocating saw.  Depending on the steel, you may need more than one blade.

Round... hole saw

Square ... Drill 4 holes at each corner and use a saw to connect the dots.  File or grind the edges smooth.  Leaves a stress free hole that won't propagate cracks.

That would be a very, very heavy trailer.

 I didn't catch the thickness in the OP .... Beware of cutting a large hole in a structural member...  You could weaken the trailer to collapse

The hole needs to be round and I just guessed at the thickness.  Come to think of it, a 1/4 inch does sound thick...the trailer is made of standard steel.

Thanks to all for the advice.

I suggest making your center pilot hole first, the using the hole saw. Center the hole saw in your pilot hole. Use a heavy-duty drill.

Use a bottle of oil - those little bottles with the tiny squirt top and apply oil frequently to the drill bit AFTER you get it started. The oil will reduce the friction and help the bit cut through the steel.

Or...like me, take it to an RV place and let them do it and install the cover/vent. : )

Hole saws are connected to pilot drill bit via an arbor...

I think the best way would be to use a plasma cutter.  Most welding shops should have one.  It will cut 1/4 no problem and will do minimal damage to paint.  Plasma doesn't get as hot as a torch.  Be ware of cutting structural members.

Yes - BUT - if you are trying to control a hole saw on sheet metal - they tend to skitter around. It's much easier to drill a 1/4 inch or so hole, then use that to anchor the hole saw.  It also helps tremendously with the accuracy of placement.

Actually you mark the metal by using a center punch.

If you own one. : )  I have a very well-outfitted shop for the most part, but steel working tools are in limited supply. 

Same as with a plasma cutter - oh yeah... like everyone's got one of THOSE in their shop. NOT.

I have found, over the years, that when people ask questions that appear to have obvious answers - it's because they do not have the experience that many other people do - hence, I find it's easier to give as much information as possible.

Now, if the others who mentioned using a hole saw had said "First get a center punch to mark the center of your hole ...." then I probably wouldn't have said anything. I only know that when I tried to do something like that (withOUT center drilling or punching)... I had a heck of a time. Hence, I took my steel trailer to an RV place and had them cut the hole and install the device. The technician then explained to me about using a drill first. I already knew about applying oil to make the cut go better. I have been using the 3-in-oil everyplace I have drilled into the frame - which is thicker steel than the panels.

    OKAY?

I guess when you run a farm you have equipment that you just ASSUME......other people have...

Actually having someone else do something, like drilling holes in things that are important to you makes sense...because if THEY screw up, you can SUE THEM to make it right...

Versus the rest of us that chalk an error up to experience...which explains how we come to know quite a few things...lots of errors...