Drilling rock with any rig, even large million dollar truck rigs is slower than drilling other formations.
First of all, use the smallest bit you can, 3 to 4 inches would be best, smaller the bit, the faster the penetration will be.
To drill hard rock, you need a better drill pipe and better bits. Steel tooth tricone rock bits are for soft rock, if you have real hard rock, you will need carbide button tricone rock bits with weight against it. Rig should have Power down for rock, or several weighted drill collars.
The worlds fastest way to drill Rock is the DTH hammer ( down the hole hammer), this is basically a mini jack hammer. It screws on drill pipe like a drill bit, but works off of air instead of water. The DTH drilling is fast, but cost much more than a tricone rock bits. DTH start at 2500.00 for a 4: hammer, and you still need a 500.00 bit and a 20,000.00 air compressor to run it. On hammer drilling, the larger and deeper the Hole the more CFM's of air you need. Remember the DTH is great in hard rock, but if you hit soft formations it is useless; if you have a place where you have soft and hard formations, you may have to switch bits and DTH back and forth.
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