On Thursday, June 7, 2018 at 1:59:29 PM UTC-7, Puckdropper wrote:
I need to make 8 rather large holes, about 3-3.5" in pool steps that have
already been installed. They're 2x12 pressure treated boards.

Spade bits that big would be TERRIBLE in soft wood - grabby and splinter-producing.
Drill a pilot hole for center, and use a deep hole saw with a (waxed?) solid rod as its pilot
(it's a nuisance to make the pilot hole at the same time as the hole, you can't see where the
center is). If the hole saw won't do the full 1.75" depth, you can chisel out some of the wood
and keep on pushing.

Compressed air gun is the quickest way to get sawdust out of the kerf (hole saws need this
every few seconds of cut). If the treated wood is toxic, use a vacuum as well.

I've used expandable auger-type bits, but they usually have a fixed screw-feed center,
aren't easy to get started, and splinter at finish (unless you have access to both
sides of the step... and 'a lot of space to maneuver'. That's probably a no-go.