Drilling in rock is always slow, even for professional truck mounted drilling rigs; fortunately many places in the country will only encounter a few rocks, and the others will often have water relatively near to the ground and so will not need to drill as deep.

With rock drilling, the problem is not so much the slipping, as it is with clay, or the removal of tailings from the bottom of the hole, as with sand; instead, rocks need grinding action. And for that, within reason, the more surface area the better.

This bit is designed differently in several ways; for one thing, it isn't sharpened, and doesn't need to be; the drilling face is rough carbide. There will be no "cutting" action in the rock, only grinding, and for this it is the surface area contacting the rock determines how fast you can drill. Another thing which is different is that it has three wings instead of the General Purpose Bit's two.

All in all, if you anticipate a lot of rocks in your well, this may be a well advised purchase. Of course, this bit will also drill adequately in other types of strata, although not perhaps as well as the bits designed specifically for that soil.

In our experience this bit often cuts rock 2 to 3 times faster than the general purpose bit, and resists wear much more strongly.

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