Decided to take a day off from casting and went back to the fundamental idea of drilling granite with sand and copper tube..
After a day of messing around with an electric pillar drill , a De Walt battery hand drill.. a piece of modern 22mm copper tube.. and some ordinary builders sand
I had been trying to drill a piece of polished granite .. so decided to try a piece of rough cut grey granite..
I gave up on the pillar drill because I sensed that one needs to develop a certain amount of skill in terms of pressure, speed and angle..
The battery hand drill allowed me far more control over the drilling.. over time I developed a "feel" for it which is essential..
Getting started was a problem so I managed to chisel a small depression in the granite to act as a pilot. This prevented the tube from skipping all over the place..
I put sand into the depression, started drilling and it just spat the sand out..
so I tried damp sand .. much better.. I could feel it cutting/grinding.
I added more water.. Eventually the wet sand then turned into a kind of "paste" about the consistency of toothpaste.. I had an assistant pushing the sand against the drill with a stick
Now I could really feel it start to cut.. after a few minutes drilling I washed the "sand paste" off to check it out..
There was a shallow ring about 0.5 mm deep..
I mixed more wet sand.. the consistency is critical.. too wet or dry and it won't work.
same again, no real progress until after about one minute , then again the wet sand turned into a paste.. It's really obvious when this happens.. although difficult to describe.. and again I could feel it begin to cut.. so I carried on..
After about another two minutes the sand paste started to turn dark grey.
Obviously granite particles are mixing with the sand.. at this stage I could really feel the drill bit chewing into the granite. which makes sense..
so I carried on all the time my assistant adding water and sand and keeping it piled up around the drill bit..
I kept drilling for five minutes..As the "sand paste" turns darker grey the cutting becomes better..
So after five minutes drilling with sand/granite paste I managed a 5mm cut.
I used ordinary builders sand.. No ruby's or diamond's.. just ordinary sand. MYTH BUSTED!!
Drill speed was variable depending on how it "felt" but I'd say average about 200-300 rpm..
The granite was grey granite..
At the end of the drilling the paste was very dark grey so I'm guessing it consisted mostly of granite particles.
The end of the copper tube was clean and polished.. no sand or granite particles embedded.. So that's another MYTH BUSTED!!..
I think what had happened is that I had, produced by accident , first a sand grinding paste, that eventually became more of a granite grinding paste.. which seemed to work well. the paste consistency is critical and you need to develop a skill and feel for it .. I don't know how much the drill wore down didn't bother to measure..
So there you have it
Granite can be drilled with copper but it is very difficult.. and requires skill and know how.. The secret's in the grinding paste consistency.. Get it wrong and it will not work.
I was very pleased with the result..
Now I have to make it work with a bow drill.. :)
Post Edited (07-Jun-14 20:22)