If you're still trying to hog long pockets by end-milling - and breaking tools in the process - plunge milling could solve the problem. When end milling long pockets, cutting forces can cause deflections along the tool's X and Y axes resulting in work-piece dimensional variations. These forces can lead to tool breakage. On the other hand, with plunge milling, the cutting force vector runs straight up the tool center-line, so you can cut with more force without fear of bending or snapping the tool. Plunge milling works much like drilling: plunge straight in, withdraw, step over plunge again, and so on. Since all the cutting force vectors are right up the tool's strong centerline, you can safely feed faster by plunging along the Z axis than by end-milling along the X and Y axes. Plunging leaves a scalloped wall, that may require finish milling, depending on tolerances and size of the stepover. Plunge cutters also have built-in chip evacuation capacity, so blast air or liquid coolant is helpful but not required on vertical setups.
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