Conventional, or manual, milling machines are primarily used to machine flat and angled surfaces by feeding a workpiece into a rotating cutting tool to remove material. They are also commonly used to position work more accurately for the same type of holemaking operations than can be accomplished with a drill press. By combining these operations, components can be machined to countless desired shapes.
Calculating spindle RPM for milling operations is the same as calculating RPM for drill press operations. Use the standard formula RPM = 3.82 X CS / D where CS = cutting speed in surface feet per minute and D = diameter of the cutting tool. Milling machines also use IPM (inches per minute) for power quill feed settings. To calculate IPM, the following formula is used: IPM = FPT X N X RPM, where FPT = feed per tooth, N = number of teeth, or flutes, of the cutting tool, and RPM = spindle RPM.
Holemaking operations are performed on the vertical milling machine. The work can be precisely moved using the table and saddle movements to align the work with the spindle. The digital readout (DRO) can also be used to create precise spacing between hole locations or between edges and hole locations. It is a good practice to lock both saddle and the table before creating holes to ensure that neither moves during the actual machining operation.
When the location of a hole from a reference edge is more critical, an edge finder can be used to very accurately find a reference edge. Carefully move the table to bring the edge finder in contact with the edge of the workpiece. Continue to slowly move the table. Notice that the tip will begin to run more true as the workpiece pushed the tip into alignment with the shank. When the tip "kicks," the position of the center of the edge finder (and the machine spindle) is one-half of the edge finders tip diameter from the edge of the workpiece. Every time you remove the workpiece from the workholding device, make sure that you know the reference '0" position from the edge of the workpiece so you can reestablish the coordinate locations from the same edge. Follow these steps to machine holemaking operations:
A pocket is an internal part feature machined into the surface of a workpiece. Pocket location and size can be controlled by using the DRO to monitor table and saddle movements. Follow these steps to machine a pocket: