Workpiece Shape
Vises, by virtue of their two parallel jaws, are less effective when needing to hold a variety of old shaped workpieces, round workpieces workpieces that are round, or any workpiece that does not have two perpendicular surfaces. Operators commonly use scrap material of nearly any shape to kind to act as a “shim” to support unique workpieces in a vise. If the workpiece is “close enough” to parallel the machinist is likely to deploy their hammer, or a breaker bar, to apply “maximum” force to the vise; often resulting in damage to the workpiece, vise, or Machine Tool. To compensate for this shaky set-up they will typically slow the speeds and feeds of the Machine Tool to reduce the force applied to the workpiece; slowing production.
Jaw Lift & Downforce
Application of in-line clamping force exerts extraordinary pressure on the base of the vise. As the two jaws move together, applying force to the workpiece, the base of the vise is also bending, however minimally, upwards towards the workpiece, like an arch. Additionally, if the base of the vise is very rigid but the connection between the vise jaw and the lead screw or base is not very rigid the jaws can begin to flex up and backwards. This can result in the operator exerting more and moremore effort on the lead screw while the workpiece receives less and less clamping force.
Jaw lift can be measured using a dial indicator.