While looking into workbenches, I came across a suggestion that scaffolding screw jacks could be used to make a large vise, but also comments saying that since they’re designed for use on muddy construction sites, the threads have excessive clearance or slop. Is that a problem in practice? I can’t figure out why it would be, since I would think backlash just means you need an extra fraction of a turn when switching from tightening the vise to loosening it. What am I missing?
You’re correct that slop in the threads just means some extra backlash. I could see, depending on the construction of the vise, having some axial play due to that slop being bad, but vises usually have some other means to control movement in that direction. The only thing the threaded piece does is push or pull.