drilling stone

[avocado]

I'm using a cordles hammer drill w/ carbide bit to drill 3/8' holes in small stones (1" X 3" or so) which are likely granite. After 10 minutes of drilling I have a 1/4" indentation and a dead battery. Is there a technique I'm missing or am I just impatient?

[jOe~]

I use a cheap but big Harbor Freight hammer drill thats almost always on sale for $40 (includes 4 bits and a chisel point) . A few days ago I bore a 3/4" hole about 8" deep in granite in not much more time than it would have taken to drill wood. So I think that maybe your stones are really hard, but more likely your hammer drill is under powered. My small hammer drill doesn't do half the job of the big one. Cordless tools often don't have much poop. Your solution may be $40 away.

jOe~

[jvc stone]

Hard stone like granite needs good quality bits, and a drill up to the task.
Dribbling a little water on the drill bit sometimes helps by keeping the bit cool.

Cordless isn't going to do the job for you.

JVC

[avocado]

thanks for the hammer drill advice. I've rented a Bosch Bulldog with a diamond carbide bit. After working out how to keep my vice from unfastening due to the vibration I'm now splitting every rock I've tried. about a third of an inch into it the rock cracks or falls a part. High speed v. slow? More drill action than hammer? I'm not putting a lot of manual pressure on it just enough I think to stabilize until there's a bit of a hole to guide the bit. what do you think I'm doing wrong?

[G. Murdoch]

Hi Avocado,

I have experienced the shattered stone problem myself, especially on rocks as small as those you are drilling. The best solution would perhaps be a diamond bit, no hammer action, run wet on a drill press. Good luck.

Graham

[fused]

Speed and heat can both be detrimental to the process, so if you use high speed don't let your drill bit get too hot. One possibility is drilling a smaller "pilot hole" first --1/8 or so-- and finish the 3/8 hole from both sides of the stone, which will keep a chunk from popping out the backside when you break through.

Are these stones black or dark in color?

[tobias]

Ah just a note it was posted earlier to dribble water on your bits to keep them cool Do not quench hot carbide it will shatter. As for drilling a pilot hole bosch sells carbide bits that have a sort of double tip. this should reduce the need for drilling 2 holes.

[desertrock]

I'm with Murdoch. I drill all my holes with a diamond core drill bit. If your depth is under say 4" you can buy diamond core bits ranging in size from 1/2" up to 3-4" at most diamond tool stores that supply stone workers. These bits are very reasonably priced. These fit into a standard drill chuck, and can be used wet or dry (wet lasts longer). If your doing a lot, it may be worth investing $150 into a water feed adapter that fits into a standard 3/8" drill chuck and has a 5/8-11 threaded male side to screw a longer bit with a female 5/8"-11 threaded opening.

http://www.diamond-drill-bit-and-tool.com/Diamond-Drill/Default.htm?Diamond-Drill-Bit.htm