Carrying on from what reno is saying,
I come from an engineering (Blacksmith/welder) background, I've always favoured holesaws, not the cheap old rubbish at the DIY stores, but the Tungsten tipped ones, from 16mm upwards to 150mm diameter.
The key to using a holesaw properly is keeping it wet with cutting lubricant, just like any other tool when cutting steel or any other metal for that fact.
If that tool face gets too hot, you will ruin the temper of the tool, rendering it useless, as the teeth wear more after the temper is lost.
