bolting with power or hand

Has anybody done both? I've only placed bolts by hand, and can manage about 15 holes per bit

Oh... 30 or so with a power drill. And that's drilling at least 3 or 3.5 inches each. Shouldn't you be going a bit deeper than 2.5 ?

I think hole depth is relative to what type of rock you are drilling in. A 2.5' hole is just fine in good granite but would be way sketchy in soft sandstone. If you are getting 30 holes with your power drill bits the rock you are drilling in must not be that hard. Its all relative.

Mike '1 hole per wrist' Schaefer

Sure.

I'd rather be a bit conservative and err on the side of safety, that's all.

No-one will judge you harshly for doing that. Bolting in rock is an inexact science. Any extra safety margin has got to be a good thing.

Cheers, Tim 'half by three and a half' Marsh

i've done a fair bit of both styles. you will certainly get more holes per bit with a power drill. how many is going to depend more on specifics of the rock (even granite varies). you should expect to get at least 30-40 holes per bit if you're only going to drill 2 1/2' deep holes. The drilling time will increase as the bit gets duller. the carbide can be resharpened by a sharpening shop for about $5 per bit (much cheaper if you have several bits to sharpen at the same time) and you should be able to resharpen at least a couple of times. you will know when a bit has lost its life when the bolts become much harder to drive into the holes. this happens because the sides of the carbide wear off with time causing you to drill a hole that is in reality not the true dimension, but slightly smaller.

hope this helps .

From all the rebolters replacing bolts for the ASCA in Yosemite, 15 per bit by hand is normal for Yosemite granite for expanding a 1/4' hole. Fewer would be expected in fresh holes; more in softer rock. Some people switch out earlier, especially for drilling on lead. I've had one bit last 30+ holes in Yosemite - and I've broken identical bits in 5 bolts. The harder you strike the hammer, the more quickly the bits break. Bits almost always break (chunks off the tip) in Yosemite granite, as opposed to getting too dull, but it will depend on the rock.

Usually drill bits last a lot longer power drilling, but on super-hard granite like Calaveras Dome, they wear just as quickly. Likewise for hand drilling, the super-tough rock found in the best of the best Yosemite granite (e.g. Good Book, Rostrum) will break the bits more quickly (and take up to twice as long to drill with a fresh bit).

The major tip for extending bit life is quick lighter blows as opposed to really going at it.

Greg Barnes ASCA Director