Rabbit, This depends on the material you need a 4 1/2" diameter hole through. If wood, then use a regular 4 1/2" bit and drill as deep as possible [about 2"]. Then chisel out the waste. Drill again. Repeat chiseling. If possible access from other side, use a long 1/4" aircraft extension bit to extend your pilot hole all the way through and use the hole saw from the other side. This will create a nice exit hole. If concrete, layout a 5" circle around your point. Along the circumference, drill a series of 1/4" hole with a SDS rotary hammer about 1/2" apart. Then enlarge these holes to 3/8". Then to 1/2" Eventually the holes will wander into each other. Then attack the remaining webs between them with a chisel point and the rotary hammer -- such as the Bosch Bulldog -- set in "hammer only" position. If steel: What? 5" of solid steel. Did a structural engineer OK this? Perhaps a plasma cutter or a big blue wrench. Consuly Hougens for a rotary broach. Maybe a trepan. ~Peter
Re: Hole Saw#67826 07/20/0612:25 AM07/20/0612:25 AM
It is a piece of steel channel under a rooftop unit. Rubber roof, so burning is out. I'm not sure of all the details as it is another PM's project. I told him if it existed the ECN guys would know. Will probably wind up making one. Thanks for all the help!