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12 degrees of freedom
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The collective range of possible directions that a workpiece could move. An unrestricted workpiece has twelve degrees of freedom.
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3-2-1 method
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A workholding rule defining the minimum number of contact points necessary to properly locate a rectangular part in three planes. The primary datum requires three points, the secondary datum two points, and the tertiary datum one point.
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adjustable locator
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A locator that can be adjusted to accommodate variations in workpiece dimensions. Adjustable locators are less accurate than fixed locators.
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auxiliary locating feature
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A part of a workpiece included for the purposes of workholding that is not related to the use or function of the workpiece.
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axes
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Imaginary lines that pass through the center of an object. Axes are used to define the location of objects in the Cartesian coordinate system.
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axial degrees of freedom
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The potential direction of linear workpiece movement along its axes.
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Cartesian coordinate system
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The system that describes the location of an object by numerically expressing its distance from a fixed position along three imaginary linear axes.
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clamp
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A workholding device that maintains the position of a workpiece by holding it in place against locators.
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concentric locator
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A locator whose center aligns with the center of a circle in a workpiece.
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conical locator
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A locator used to position a cylindrical workpiece by self-centering the workpiece on a cone.
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cutting force
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A force generated by the motion of the cutting tool.
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datum
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A surface that is assumed to be geometrically perfect or that acts as a reasonable surface for the purpose of workpiece location.
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fixture
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A customized workholding device used on machine tools to position and hold a part during various machining operations. A fixture is built to hold a specific part design.
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holding
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Maintaining the positioning of a workpiece. Workholding devices maintain, or hold, the workpiece in its desired location usually with the aid of clamping devices.
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locating
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The process of positioning the workpiece in a designated location. Locating is also used to describe the precise positioning of the workpiece in the horizontal plane.
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machine tool
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A power-driven machine that uses a cutting tool to create chips and remove metal from a workpiece.
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machined hole
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A hole that has been shaped by a cutting tool. Machined holes are more accurate than cast holes.
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machined surface
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A surface created by the removal of metal during a machining process. Machined surfaces are generally accurate and are preferable for locating a workpiece.
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metal cutting
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A machining process that uses a tool to create chips and remove metal from a workpiece.
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milling machine
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A machine that uses a multi-toothed milling cutter to remove metal from the workpiece surface to create flat and angular surfaces and grooves.
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perpendicular
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An angle formed by two lines at a right angle. The corner of a piece of paper is formed by perpendicular lines.
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positive stop
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A locator into which the part is directed by primary cutting forces generated by the cutting tool.
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primary datum
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The first plane of the 3-2-1 method determined by three points. The primary datum usually coincides with the largest surface of the workpiece.
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radial degrees of freedom
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The potential rotational direction of workpiece movement around its axes.
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redundant location
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A situation in which a workpiece has more locating points than it actually needs. Redundant locators increase the chances of errors in manufacturing processes.
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secondary datum
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The second plane of the 3-2-1 method determined by two points. This plane must be perpendicular to the primary plane and is usually the second largest surface of the workpiece.
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sight location
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A rough locating method used as a first step. Machined details are usually created in this step for further use and better precision.
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support
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The process of locating from underneath the workpiece. Supports generally restrict motion down along the Z-axis.
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tertiary datum
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The third plane of the 3-2-1 method determined by a single point. This plane must be perpendicular to both the primary and secondary planes and is usually the smallest surface of the workpiece.
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unmachined surface
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A surface that is less accurate than a machined surface. Cast parts have rough, unmachined surfaces.
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vise
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A workholding device with one fixed jaw and one moveable jaw. Vises are often used to hold simple rectangular or cubic workpieces on a mill or machining center.
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workpiece
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A part that is being worked on. It may be subject to cutting, welding, forming or other operations.
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X-axis
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The linear axis representing motions and positions along a line parallel to the longest edge of the worktable.
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Y-axis
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The linear axis representing motions and positions along a line parallel to the shortest edge of the worktable.
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Z-axis
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The linear axis representing motions and positions along a line perpendicular to the worktable.
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