On Oct 6, 11:28 pm, willshak wrote:
When I first start the drill, I can see the crushed concrete powder
coming out and forming a ridge around the hole. All of a sudden the
powder stops building and I can hear the drill bit kinda bouncing over
something. The bit never stops turning, it just stops cutting.
I wash out the hole and look in. The aggregate filler in this concrete
is small roundish pebbles, about the size of a green pea up to a lima
bean size with colors of yellow, orange, grey, or whitish. I may see
parts of one, or two, or maybe three pebbles intruding in the hole, the
tops of which look sanded from the drill rather than cut. At this time I
take the small sledge and a 12" long steel tapered flat nosed punch with
a 1/4" wide tip and try to crack the pebbles into smaller pieces that
the drill bit can handle. I think that the 3/4" hand tool star drill can
do a better job of cracking the pebbles with fewer blows since the star
drill will completely fill the hole and may crack two or more pebbles
with one blow.

Bill,

I know "rent a hammer drill" is not the answer you're looking for.

Still, it is the best advice for your situation. With a hammer drill,
you will NEVER have to stop to bust up the aggregate. A hammer drill
will bust right through on its own.

The amount of time and money you spend running around looking for a
star bit will more than offset a 4-hour rental on a hammer drill.

Drill 20 holes with your regular drill, using the star bit every time
you run into a pebble. Then drill the other 20 with a hammer drill.
You'll wonder why you even bothered with the star bit.