When I use a hole saw on anything thicker than a mm or two I drill a hole or two, say 4-6 mm, on the circumference. It allows the swarf to clear. Without it the gullets just clog up and stop cutting. Anything to lubricate and wash the swarf away - wd40, oil, whatever you have handy.
I also use the mill or the pillar drill if possible, and a slow speed.
I also use the mill or the pillar drill if possible, and a slow speed.