how to drill post holes in solid rock

[klim]

I need to drill many (50 to 100) 1 1/2" diameter holes 6" deep in solid rock for steel T-posts for a fence and I haven't decided how to go about it.

What type of bit/drill combination would be most cost effective? Electric drill (size?) with core bit? Pneumatic drill with impact bit? Other combo?

The location is far from power so the job would require a portable generator or a compressor if a pneumatic drill was used.

I have a 2hp 20 gallon compressor - would be sufficient to run a pneumatic drill to drill the 1 1/2" holes?

[Joseph Meehan]

Call in the pros with the commercial equipment. It will be a lot cheaper in the long run.

[Toller]

I haven't any idea, but know enough to ask if it is granite or shale.

[SteveB]

Rent a core drill?

As suggested, it MIGHT be cheaper to have someone do it. It WOULD be a whole lot easier. You might be opening a bag of snakes.

Steve

[DanG]

Way back when some friends and I generated a bid for 8' cyclone in extremely rocky soil. A California company came in 40% lower than any other local outfits. We went out to laugh thinking they would not be prepared for local soil conditions. They had a heavy steel dome, inserted approximately 1/4 stick of dynamite. When the charge went off, the lid was upside down next to the hole ready for the next load and the hole was clean to the bottom waiting for the post and concrete.

Don't ever assume the low bidder is nuts. These guys went all over the world setting fence.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing. . . . DanG

in

how to

portable

[R.C. Crawford]

Rent an 90 cfm air compressor and a drifter drill. Most equipmet rental companies rent these items. Get a drill bit to fit the drifter that is equal in diameter as the maximum size as your post. Then drill by going down about

6 inches and lifting the drill to within 1" of the top of the hole. continue this until you reach the plan depth of your hole. Once at the bottom flip the lever of the air drill to blow out the hole. There are usually three positions for the operating lever on the drifter drill. There is one that shuts it off. One that drills the hole and one that blows air to the bottom of the hole to clean out the cuttings. It is important that when you rent the drill, you show rent two drill bits. One is to be used to drill and the other is to be used in case you lock up the first drill bit. If the first bit gets locked in the hole, then simply use the second bit to drill beside the other bit to relieve the pressure and remove the bit. Wear heavy duty clothing and steel toe shoes when working. Safety glasses are best due to the fact that the high pressure air will blow cuttings into your face.

Make a plywood template that you can secure to the ground with your foot or other item to hold the bit in place on unlevel ground. Becareful not to let the plywood spin and cause injury.

Spend some time and plan a safe work experience. Expect the work to be very energy consuming. Watch for hand injury due to the vibration of the drill.

Good luck.