Bench Vise
The nut in which the screw turns may be split so that, by means of a lever, it can be removed from the screw and the screw and moveable jaw quickly slid into a suitable position at which point the nut is again closed onto the screw. Many fitters prefer to use the greater precision available from a plain screw bench vise. The bench vise may include other features such as a small anvil on the back of its body. A bench vise screw is usually either of an Acme thread form or a buttress thread. Those with a quick-release nut use a buttress thread. In high production machine work, work must be held in the same location with great accuracy, so CNC machines may perform operations on an array of bench vises.
To assist this, there are several machine-shop specific vises and vise accessories. Hard and soft machine jaws have a very important difference between other metalworking bench vise jaws. The jaws are precision ground to a very flat and smooth surface for accuracy. These rely on mechanical pressure for gripping, instead of a rough surface. An unskilled operator has the tendency to over-tighten jaws, leading to part deformation and error in the finished work piece. The jaws themselves come in a variety of hard and soft jaw profiles, for various work needs. One can purchase machinable soft jaws, and mill the profile of the part into them to speed part set-up and eliminate measurement. This is most commonly done in gang operations, discussed below.
For rectangular parts being worked at 45 degree angles, prismatic hard jaws exist with V grooves cut into them to hold the part. Some bench vises have a hydraulic or pneumatic screw, making setup not only faster, but more accurate as human error is reduced. For large parts, an array of regular machine bench vise may be set up to hold a part that is too long for one vise to hold. The vises' fixed jaws are aligned by means of a dial indicator so that there is a common reference plane for the CNC machine. For multiple parts, several options exist, and every machine bench vise manufacturers have lines of vises available for high production work.
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