I have asbestos shingles and i need to vent a portable a/c so i'm going to replace a few shingles with fiber cement board so i can cut them. i heard these things are a nightmare to cut.
if you only need it for one hole get a cheap one, cement board is hard on any hole saw so i have saved my good ones and bought throw aways. if you want a good one buy Milwaukee, there still made in USA
Go to any rental place they rent these drills and bits that have diamond tips for cutting concrete. And use water to hold down the dust. Should have any size you need.
here's a cheap way to do it...using inexpensive drill bits (carbide/masonry), if you have them, begin drilling many small wholes along the inside of the circle pattern you have drawn until it can be easily chipped away...after installing whatever it is you need, caulk it very well. Practice safety, of course. These shingles can be very brittle and will break if you are not careful. go easy.
A jig saw with a metal cutting blade will work. First, trace the hole you wish to cut on the surface, then drill one hole big enough for the jig saw blade to fit through. Then simply cut out your pattern. CAUTION! Don't breath in the dust since asbestos is a carcinogen. Get a filter mask at any hardware store.
