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Moldmaking Report: ABCs of machine movement — Part II

In the last regular Tooling Tips column (Dec., '01) I discussed some of the basics of spatial orientation in CNC machine tool movement. One of the most fundamental prerequisites for correctly setting ...


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March 1, 2002 by Mark Benoit -- Tooling Tips

In the last regular Tooling Tips column (Dec., ’01) I discussed some of the basics of spatial orientation in CNC machine tool movement. One of the most fundamental prerequisites for correctly setting up tools and workpieces is a grasp of the concept of the Cartesian coordinate system.

The Cartesian coordinate system is based on a number of intersecting, parallel and extended axes labeled A, B, C, P, Q, R, U, V, W, X, Y and Z. In the last column I reviewed the Right Hand Rule, which is used to visualize the spatial relationship between the X, Y and Z primary axes; and the Right Hand Rotational Rule, which is used to find the positive direction of the corresponding rotation axis, A, B or C.

I will now discuss the relationship of the additional axes, U, V and W to the primary and rotation axes. The X, Y and Z axes help us define linear and rotational movement in a work envelope. Many horizontal machining centers have a quill that can be extended, as well spindle or table motion. These movements are referred to as the secondary axes of motion. When a machine has secondary motion that is parallel to the X, Y or Z-axis, it is defined by the U, V and W axes. An axis parallel to the X axis is the U axis; an axis parallel to the Y axis is the V axis and an axis parallel to the Z axis is the W axis. The U and V axes are designated on wire EDM’s, horizontal machining centers and boring mills, where the quill “W” can move in and out (see diagram).

On a wire EDM machine the upper head through which the wire is fed can move independent of the X and Y table movement allowing for taper cutting on contours. The movement of the head that controls the wire independent of the table are the U, V axis respectively. Each axis could in turn have a rotation axis P, Q and R. The U axis has a P rotational axis, V axis has a rotational Q axis and W axis has a rotational R axis (see the table below).

Understanding and applying these basic concepts of spatial orientation is a prerequisite for avoiding errors and making consistently high quality molds from CNC machines.