On Fri, 12 Mar 2010 12:53:21 -0500, "EXT"
wrote:


wrote in message
.. .
I've got myself into a situation -
I need to drill through 6 2X8 joists which are accessible only from
the one side. They are spaced 2 feet on centers. (need to pull cable
across to the center of the floor). The joists are sitting directly on
concrete, and the decking is 1 1/2" (you read that right) plywood.

What is the lowest power-requiring type of drill to use/ since it
needs to be run on a 12 foot long extension-----.
I tried a speed-bore type spade bit, but it has a bad habit of
"catching" just as it breaks through - putting a severe strain on the
connection between the bit and the extension.

Would a forstner type work better? Or an auger?

Still looking for a viable bit extender setup as well - thinking I
might need to go to 1/2" steel waterpipe with a 7/16 or 1/2" hex shaft
welded into the one end for the chuck to grab. In 3 or 4 foot length
with couplers it should be handleable?

I don't see any drill working, as the shaft diameter is always much smaller
than the drill bit. To drill 6 joists with a 1 1/2" bit means the bit will
drop about 5/8" with each hole as the shaft rests on the previous hole
bottom, 5/8" x 5 joists (I am assuming the first hole will be accurate) = 3
1/8", so you will either have to start real high on the first hole or hit
the concrete with the last hole. I cannot think of any way of getting such a
large hole drilled through so many joists in one go. Can you not go around
the ends and come in from there some how?

Absolutely no way.

And I did it today. Started with the first hole just clear of the
decking - ended up abot 3 inches down from the decking at the other
end.. And I had something like 15 inches of joist to play with.