Something to remember on hole saws, run em as slow as you can and use lots of lube.
50 to 100 rpm on something over say 1.5" is highly recommended. Run them too fast, and they'll ruin the teeth, or heat up and work-harden the steel you're trying to cut thru to the point you can't cut it anymore.
Hard to do with a hand drill or most cheaper drill presses, as they don't go that slow.
Walked in to my shop at work a while back, and one of the new guys was trying to hole-saw a 2" hole for a panel mount air gauge into a panel, running in high range on a big cordless drill. Squealing like crazy and sparks flying!
I had to finish it with the plasma cuter due to the fact he got it so hot, couldn't even touch it with a new hole-saw.