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?
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?
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. . . .
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
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
Watch for hand injury due to the vibration of the drill.
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