Dear Guys,
Last fall, I asked for advice as to how to drill holes in one inch slabs of slate, outdoors, without cracking the slate. I got lots of good advice, and followed one in particular.
I needed to drill half inch holes. I bought a plug type bit, with diamond coated edge, at Home Depot. Cost was around $20. I had trouble finding an arbor to fit it, but finally found that the bit would fit into the end of a 1/2 inch socket driver extension, and that the other end of the extension would chuck-up into my large hammer drill.
To keep the bit from wandering, I laid a piece of 1 by 6 cedar board down on the slate, marked where I wanted the holes to go, and then lifted up the board and drilled out 3/4 inch holes in the board on the marks. After laying the board flat again, the bit would fit neatly into the holes, with a little room to spare, which was good because alot dust will be brought up by the bit.
I did not use the hammer setting on the drill, just the regular drill setting.
To drill each hole, I had someone standing by with a bottle of water, and had him pour a little bit of water in the hole, at the beginning, and at each time I pulled the drill out. I then started drilling, on very slow speed, letting just the weight of the drill put pressure downward, and not pushing with my weight.
After an initial circular groove was cut in the stone, I pulled out the bit, added water, and then started drilling again at a slightly faster (but still pretty slow speed). I then pulled the bit out for every quarter inch of depth, and cleared the stone plug out of the center of the bit.
This was all pretty messy, since I was sitting down on the stone, and the water and stone dust are everwhere. (You get a wet bottom). But, I was able to cut 10 perfect holes in the slate, to a depth of 1.5 inches, without a single crack. (Beneath the slate was some type of thin set.) It took about 10 minutes per hole.
Again, thanks for the advice. The key is to get the diamond bit, keep the bit wet, go slowly, and have a heavy drill.
Best Regards, Mannyrock
