On Wed, 12 Aug 2009 13:58:41 -0400, "Joe AutoDrill"
wrote:

I get all kinds of requests... And this one has me stumped.

A customer was at a Football stadium and noticed a contractor with a
dual-headed hammer drill on a jog of some sort. It was used to make the
holes for the stadium seating.

He wants to buy one from me (not gonna happen!) but I told him I'd point him
in the right direction.

On topic portion - He swears they went through the aluminum and concrete
with the same bit and stroke and it was 100% definitely a hammer-drill when
it got to the concrete (not just spinning, but pecking in and out and
impacting the concrete).

Anyone heard of such a thing?

If the guy makes a living installing stadium seating by the
thousands of seats per client visit, you'd almost have to come up with
a custom drilling jig to make the holes en masse. Your arms would be
falling off before lunch time if you didn't.

I'll bet he isn't drilling on the aluminum jig - the jig is most
likely premade with HSS bits, and the holes are used to position the
carbide concrete bit to get the holes in the right spots. No bits
hitting extra hard aggregate chunks and drifting off to one side.

I can see in my mind exactly how it would have to work...

You make a modular template that matches the seat layout, and the
various template segments have pivot points to snap/bolt together so
the bends work like the seats need - You rarely see the seats all in a
perfectly straight line, the whole row curves. Especially notable in
places with curved peristyle ends, like the Los Angeles Memorial
Colliseum (1984 Summer Olympics), the template makes the holes then
then they just drop the seats in place and grab an impact wrench.

The hard part IMHO is finding small electric hammer-drills that can
take the abuse of almost continuous running. Might even have to run
external forced air cooling into the motors to keep them from melting.
I wouldn't even try to make a multiple spindle head with an impact
mechanism.

A mobile drill rig isn't that hard to fabricate - a cart with solid
rubber casters, vertical rack, and space for some convenient ballast
like sandbags or shot bags. Could even carry the vacuum cleaner and
have a ring adapter to catch the dust around the bits as it drills.

You would have to come up with a clamp that holds the drill motor in
position in the drill-press vertical carriage, but allows for quick
changes when one drill motor dies so you can quickly swap in a spare.

-- Bruce --