Jovial Monk wrote on Apr 18
th, 2022 at 11:02pm:
I needed to dismantle (undo some very long screws) some shelves from a defunct HBS and rebuild them in my HBS. There was time pressure—I would have had to pay another months rent on the defunct shop if I did not get the shelves dismantled by a date only a couple days away!
Somewhere I have a Maquita hammer drill.
I have not started emptying the shed yet—there is some goldplated plumbing fixture somewhere!
Oh, as you have found, it is harder to undo screws than put them in.
Sometimes they can be loosened by hitting the top with a hammer. Not too hard, just to jar them.
Spray it with penetrating oil, let it soak in for a while.
If you think it is getting too hard to undo them, you'll be right. Stop or the head will be stripped.
If they are in old wood, can you chisel out a bit around the head, then put vise grips onto the now exposed head ?
It's a hard job. Don't rush it.
Good luck