452 Modern Metalworking Copyright Goodheart-Willcox Co., Inc. 26.4.3 Cutter Holding and Driving Devices for Horizontal Mills On horizontal milling machines, most cutters are held and driven by arbors of various sizes and styles. Arbors with self-holding tapers are used on some small, hand-milling machines and older models of larger machines. As shown in Figure 26-24, the three basic arbor styles in general use are: • Style A arbor. Fitted with a small pilot that runs in a bronze bearing in the arbor support. • Style B arbor. Has a large bearing that can be positioned on any part of the arbor. The bearing support is then located as close to the cutter as possible for maximum cutter support. • Style C arbor. Used to support smaller sizes of shell end and face milling cutters. Both style A and style B arbors have a keyway milled their entire length, allowing the cutter to be keyed to the arbor, which prevents it from slipping during a cut. In general, use the shortest arbor that will permit adequate clearance between the arbor support and the work. It is also necessary to keep the arbor bearing well lubricated. Spacing collars, Figure 26-25A, allow the cutter to be positioned on the arbor. They are made in a number of widths and permit the accurate spacing of two or more cutters for gang milling or straddle milling. A draw-in bar, r r Figure 26-25B, is used on hori- zontal and vertical milling machines. It fits through the spindle and screws into the arbor, collet, or collet holder to hold it firmly in place. Drive keys on the nose of the spindle on horizontal milling machines fit into corresponding slots in the arbor flange or collet holder to provide positive (nonslip) drive. Photo courtesy of Grizzly Industrial, Inc. www.grizzly.com (A and C) WMW Machinery Company, Inc. (B) Figure 26-24. Basic arbor styles. A—Style A arbor. B—Style B arbor. C—Style C arbor. A B C Goodheart-Willcox Publisher Figure 26-25. A—Spacing collars are manufactured in many different widths. They are used to position one or more cutters on an arbor. B—The draw-in bar holds the arbor in the spindle. Avoid operating a milling machine if the draw-in bar is not tightened in place. Arbor Spacing collars Draw-in bar Machine spindle Arbor A B