Review on SHDIATOOL Diamond Coating for Concrete, Marble, and Granite Surfaces by Mike Ewing

Not sure how well it would work but was pleasantly surprised with the results. I bought two of these SHDiamtool bits, 50mm and 32mm, for custom work in sandstone blocks 2" to 2-1/4" thick. So I made a template out of plywood and 2x4 with the same hole sizes and layout that I need for the blocks. simply ensuring that the bit does not slip or wander upon initial contact with the stone surface. I used a water cooled drill press and checked the core bit on the speed chart to make sure I was in the ball park for the spindle speed - at 1080 rpm for both sizes - and these things cut sandstone really well and fairly quickly with only moderate feed pressure.. them after 12 holes at 50mm and 48 semi-deep holes at 32mm or buy the right mandrel for them and you should have no problem if you do cool them with water, use the right spindle speed and don't use too much clamping force.