This is a Chinese vice I bought to manufacture multiple pieces in one op. Its awesome actually and cost US$650 plus freight.

Build quality, I give it 85% but I am fussy fussy. It took a while to learn how to bring it into Fusion, and it has a couple of variable points with the wedges that need to be setup if I am machining more than 2 pieces. Anyway, I am very happy with it.

Question though, and the manufacturer has no idea, they just copied it from somewhere.

The way this vice works is the wedges are pulled down with a M16 bolt. This down force on the wedge, pushes the face to clamp the workpiece. I guess its obvious to you guys who use these types.

I do understand there is a mechanical advantage in the ramp of the M16 thread, and also there will be an advantage in the wedge yes? So if the wedge was 45deg it would be no mechanical advantage?

But today, first time its happened, the 2.5mm cut-out on the top of my jaws, actually sheared off the bottom corner of my 6061 workpiece. Both of them actually different sides. It was especially cold today but I do pull these bolts up quite tight. The force must be huge.

So my question is if I was to use a torque wrench what would I pull these bolts down to? I use up to 14mm end mills and a 45mm facing mill so I do get paranoid a workpiece might move as has happened once or twice. Can someone advise on that? Vice image attached.