Additional comments on covered lead screws:

On vises with an exposed lead screw, there is generally a guide rod that keeps the two jaws aligned, and, to keep the moveable jaw from spinning when rotational (sheer) forces are applied. Think putting a long piece of pipe in the jaws and bending down. All you have is that little ˝ or 5/8 inch guide rod to resist those forces, and of course the lead screw. When hammering in the vise.. ie.. Putting pins in place, removing bushings/bearing etc.… all the downward force is transmitted to the lead screw and guide rod. The only bent lead screws I’ve seen were on exposed lead screw vises.

Keep in mind .. these little vises were for the home shop/hobbyist types, and built to a price point.

Just about all manufactures who produced industrial grade vises used square slides and for good reason. As we all know, it’s very hard to rotate a square peg in a square hole, Due to the amount of surface area, square shapes are extremely resistant to rotational forces. On these vises the lead screw basically just “floats” in place, it takes no sheer force or downward force when hammering on parts in the jaws. I have never seen a bent lead screw on one of these…. Don’t know how you could bend one.

In the excellent article posted by keith, most industrial grade vises included a lip or “Dynamic support” as additional support for the slide when downward forces are applied.

There was also a purposeful amount of “slop” machined into these vises, so if some parts did get “tweaked” the vise would still work. I’ve seen several vises with bent slides that worked fine.

Wilton “Bullet” vises deviated from the square slide and went with a round slide, these Wilton vises rely on a small ˝ inch key stock to resist rotational forces… Not sure why, as round tubes are designed to rotated in round holes. Possibly Wilton saw the keyway as a sacrificial part, much like a key in shaft/pulley set-ups. Too much force and the key will sheer.

On these large industrial vises, the nut is generally the sacrificial part, cheap and easily replaced.

Last edited by Mike Hunter; 11/20/19 11:37 AM.