[North Wind]

I got this piece of black stone that I am drilling and can`t even put a dent in it. don`t know what kind of stone it is but it is hard.Masonry bits wont touch it.
what would you suggest I use to drill it? I need to put 3/8 and 3/4 inch holes in it.

[Keoma]

I have a set of diamond tipped dremel bits. They drill into my stones fairly well. The bit is crap house after, but it works and the bits are relatively cheap.

[slivers&dust]

try taking your piece to a granite countertop fabricator...they will use a diamond core bit for those sizes. Some of the larger concrete contractors use them also.

[AlArchie]

Sounds like you might have a piece of basalt...hard volcanic rock. You should be able to drill that with a carbide bit in a drill press at a slow (250 rpm or so) with water to cool and lubricate the cut. Just don't expect this to be a normal drilling..it's going to take time and patience.

Or you can purchase small diamond core cutters but you will still need a drill press and water for cooling. And then unless you cut all the way through, you will be left with the prospect of removing the solid core from the cut.

You might be best served by following siver and dust's advice and taking this to a counter top fabricator or maybe there is a lapidary shop near you??? They would have the necessary equipment.

Al

[cats pa]

Originally Posted by AlArchie

unless you cut all the way through, you will be left with the prospect of removing the solid core from the cut

If you don't need a smooth bottomed hole, just tap a small steel wedge into one side of the kerf. In brittle material, it doesn't take much to fracture the core at the base (assuming the material is of uniform hardness throughout).

Al, what do you think of water-cooling a cobalt steel bit? Might be cheaper than solid carbide, and less brittle itself. If it cuts, of course...

My buddy Bill installs granite counters - I'll ask him and let you know.

Update: he says that diamond bits are the way to go (sintered carbide will work on softer stone, but slower and a big PITA when they heat up) and he says if you use a drill press they cut a lot better because it holds them steady and the cutting pressure is uniform around the entire circumference and less side friction.

Parker

[AlArchie]

Parker, I'm not familiar with the cobalt/steel bits, but I have drilled basalt and granite with the standard carbide bits (1/4" and less) but used a drill press and plenty of water to carry out the slurry. I agree a diamond bit would be the way to go, but even then...a drill press and water to cool the cut. And those durn things ain't cheap, but then again neither are carbide tipped bits of 3/4" size. Expect to spend around 20 to 30 bucks for a good carbide bit.

I used a large round aluminum cake pan to contain the water so it wouldn't get all over my drill press table and chance rusting the thing up.

Al

[North Wind]

I did use a carbide bit with water in my drill press at slow speed.I will have to get some core bits I guess.Thanks for your help and I will let you know how it turns out.Does anyone know where there is a good place to them at?Vince

[susieq]

Daimond core bits in a drill press work pretty well if you can build a resivoir of modeling clay around the drill site and keep a melting ice cube in it to cool the bit as it works. The harder the rock, the hotter the bit will get.... (heat will not only damage the bit, but the rock migh split too)

I also work with bonsai and occassionally find a beautiful pot that would be perfect for bonsai if it only had drainage holes in it. So I aquired a diamond core bit years ago. Ceramic varies greatly in hardness and some things grind down pretty quickly while I have spent more than an hour on others.

With your stone, I might be tempted to get everything set up and then weight the lever on the drill press with something to keep pressure on the bit but free yourself up to do other things nearby while keeping an eye on the progress and keeping fresh icecubes on the drill site by the bit.

Diamond core bits can be very cheap or very expensive.....if you buy a good one you will get a lot more use out of it. If you plan to do this sort of thing very often, get a good one.
Best wishes for success with your project.

[AlArchie]

Vince, are you using the carbide masonry bits or the carbide tipped twist drills? the masonry ones should do the trick, but if not

Lee Valley has the diamond hole drills...check here http://www.leevalley.com/wood/page.a...180,42316&ap=1

You might also try lapidary suppliers.

Al