442 Modern Metalworking Copyright Goodheart-Willcox Co., Inc. For practical purposes, milling machines may be grouped into the two large families of fixed-bed milling machines and column-and-knee milling machines. Both families include milling machines with horizon- tal spindles and with vertical spindles. 26.1.1 Column-and-Knee Milling Machines The column-and-knee milling machine is named for the e parts that provide movement to the workpiece: a column and a knee. The column supports and guides the knee With the exception of the lathe, milling machines are the most versatile machine tools for machining metal. They can machine flat or contoured surfaces, slots, grooves, threads, gears, spirals, and three-dimensional configurations. Milling machines are available in more variations than any other machine tool. In a milling operation, a rotating, multitoothed cut- g ter is fed into the work to remove material, Figure 26-1. Each tooth removes a small chip of metal. One of the main differences among milling machines is the movement of the worktable, cutter, or workpiece. The following terms are used to describe their move- ment on a milling machine with a verticle spindle: • Longitudinal movement is the back-and-forth move- t ment on the X axis. • Vertical movement is the up-and-down movement t on the Z axis. • Cross movement (also known as t traverse movement) t is the in-and-out movement on the Y axis. 26.1 Types of Milling Machines Milling machines are often categorized by their spin- dle orientation. Those with horizontal spindles are commonly referred to as horizontal milling machines, Figure 26-2A. The cutter spindle projects horizontally from the column on these machines. The axis of the cutter is parallel to the worktable. Milling machines with vertical spindles are called vertical milling machines, Figure 26-2B. On these machines, the cutter spindle is normally in a vertical position, perpendicular (at a right angle) to the top of the worktable. The spindle can also be tilted for angu- lar cuts on most machines. Goodheart-Willcox Publisher Figure 26-1. In milling, a rotating multitoothed cutter is fed into the work to remove material. Each tooth removes a small chip of metal. Tool changer Machine shown without guarding B A Horizontal spindle Worktable Bed Tool changer Vertical spindle Haas Automation, Inc. Haas Automation, Inc. Figure 26-2. A—An example of a computer numerically controlled (CNC) horizontal mill. B—A CNC vertical mill.