On Thu, 26 Aug 2004 00:32:21 GMT, (Doug White)
wrote:

I am going to hang a METAL extension ladder using some METAL hooks. Now
that I have established some serious metal content, I need to drill the
mounting holes in the concrete garage wall. The hooks have 3 holes, and
I'm going to use plastic expansion anchors for the screws.

*Please* tell me you are going to hang the ladder using the metal
hooks and plastic expansion anchors for storage, and not for
structural support while climbing the ladder...

(For climbing support, you need something seriously beefy and
reasonably bombproof like 1/2" expansion bolts or sleeve anchors of
some sort. 1/4" plastic sleeves and #10x1" screws won't cut it.)

I have a nice Bosch hammer drill, but my past experience has demonstrated
very poor success at getting holes where I want them. The drill wanders
& bounces off pieces of agragate in the concrete, and I end up with holes
that won't match up with the holes in the bracket/fixture/whatever. I've
tried using a star drill as a centerpunch, but that only helps a little.

It seems to me that the absolute error gets worse with bigger drills, so
I can try starting small and then boring out the hole with a bigger bit.
Another option is to drill the first hole, and then use the hooks as a
jig to ensure that the subsequent holes line up. I was thinking about
using a small bit with a sleeve that fits in the holes in the metal hooks
to prevent the drill bit from chewing things up.

Any suggestions or tips from the experts out there?

1/8" carbide pilot bit carefully drilled in to start the hole as
close to the desired center as you can get it, and then a single pass
to your finished hole size. No matter WHAT you do the bit will want
to wander with the aggregate - and it's really going to wander badly
if they used quartz gravel that's harder than heck, so plan on making
one or two holes in the bracket a bit oversized or oval to
accommodate. Or punch a new hole if it moved a mile.

If you are ever making a big roof access ladder or other big steel
structure, don't weld the mounting tabs permanently until after all
the anchor holes for the mounting are drilled - if the hole wants to
wander while drilling you don't fight it, you simply modify the bolt
tab location to match where the anchor ended up...

"Don't raise the drawbridge, Lower the river." ;-)

-- Bruce --
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
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