15 years ago
Your questions hit a number of issues.
The angle - we face it with the "on the flat" bit coming out towards us. So half the holes are quite near to the corner (the holes are alternately staggered to prevent rocking (?). So problem getting a mag.base drill to line up.
The access is "single-sided" in most places, as breeze-block has already been put up and in some places the waterproof roof is already in place, so we absolutely cannot disturb that. If we had access to both sides, I could improvise a clamp or something.
I think this is simply a "pessimum" situation - single-sided access limits options, not big enough to get a big drill in, too big to be comfortable with a hand-held drill.
I've looked at this job and I see no easy way to make some sort of clamp and drilling assembly. The only one I can see is use a hand-held drill on the first hole, then bolt on a rig, going along the job one-by-one, using each drilled and tapped hole to reach the next position.
Drilling was much easier with a "pistol-grip" electric drill when had a handle set "sticking out of the top" and the drill used "on its side". However, provided polymer handle with steel band fixing was not rigid enough to take the force needed happily and I think making a big handle which clamps onto the front parallel section of the drill would help a lot.
Thanks for trying to help me out here.