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Software 32 MoldMaking Technology May 2015 The Misunderstood Cutter Path By Jeff Jaje F ive-axis machining is attractive to mold- makers because it can produce improved surface finishes, and it can be more effective for milling steep areas and pockets in molds. Achieving these goals requires an under- standing of which types of cutting paths are appropriate for such applications. A common five-axis cutter path is normal to the faces of the part. While, in milling, this often provides reduced tool deflections and vibrations, it is not always practical to machine this way on the steep areas of many molds, sim- ply because of machine kinematics. Here, we'll examine appropriate applications and methods for using normal vectors for five-axis milling in moldmaking. Force Effect Cutting tools experience force on both the tool shank and on the cutting edges. The forces on the shank are both axial, in line with the tool axis, which compresses the tool, and lateral, sideways to the tool, which causes the tool to bend. When the tool finishes normal to the faces that are being cut, the ratio of axial forces to lateral forces is higher towards the axial forces, allowing more of the cutter forces to be transferred through the tool axis. As the tool contact point moves from a normal position to sideways, the amount of lateral force increases. This induces a slight tool deflection, and since the tool is also rotating, tool vibration can occur. Milling normal means less tool deflection and Normal vectors are not always the best choice for milling complex mold surfaces. Figures courtesy of Vero Software. In this illustration, the tool axis is normal to the face of the part being milled. Here, the tool axis is tipped from the normal position to avoid milling with the very tip of the tool. It is not usually practical to mill normal to the surface when machining steep walls or pockets. FIGURE 1 FIGURE 2 FIGURE 3