![]() Head-press-fit bushings are designed for applications where heavy axial loads might push a press-fit bushing through the mounting hole. These bushings, however, are made with a head. Head-press-fit bushings, Figure 10-4, are similar to the press-fit bushing in design and application. Plain press-fit bushings, for permanent installations, are the most popular and least expensive drill bushings. This design, however, offers less resistance to heavy axial loads. The headless design allows the bushings to be mounted close together and flush with the top of the jig plate. Figure 10-3 shows recommended hole size for pressfit bushings. They are held in place by the force of the press fit. The bushings are pressed directly into the jig plate. Press-fit bushings are designed for one-step operations, such as drilling or reaming. These bushings are identified by the letter P (or PC when the bushing is carbide). Press-fit bushings, Figure 10-2, are the most common and least expensive permanent bushing. The different varieties of permanent bushings can be found below. Since these bushings are permanently installed, repeated replacement would cause the mounting hole to wear and reduce the accuracy and soundness of the installation. Permanent bushings are either pressed directly into the jig plate or cast in place. Permanent bushings are intended for limited-production applications where bushings are not regularly changed during the service life of the workholder. Drill bushings are specified by ANSI letter-and-number designations, which identify the bushing type and specific dimensions. This format consists of one to four letters to identify the bushing type, an OD size in 64ths of an inch, a length size in 16ths of an inch, and the ID of the bushing stated to four decimal positions.įigure 10-1. These letters and numbers describe the basic form and specific sizes of each bushing, in a format established by the American National Standards Institute (ANSI). The three general categories of drill bushings available are permanent bushings, renewable bushings, and air-feed-drill bushings.Īs show in Figure 10-1, drill bushings are identified by letters and numbers. Types of Standard Drill Bushings Types of Standard Drill Bushingsĭrill bushings come in a wide range of types and styles. But simply supporting the twist drill in a drill bushing can greatly reduce, if not eliminate, most of these problems. When combined, these conditions result in drilled holes that are off center, oversize, out of round, out of alignment, and usually not straight. A drill with an off-center point cuts oversized holes. Also, in most production situations, the drill point is not always precisely centered. The problems of the design increase further because of the unsupported length of the drill. In addition, the material removed to form the flutes and margins of the drill, combined with the standard back taper, greatly reduces the contact area between the twist drill and the hole. This design, although highly efficient for cutting, is not effective for centering the tool. The point formed by these angles is called the “chisel edge.” The chisel edge is normally at 135º to the cutting edges of the drill. ![]() The cutting edges are usually set 118º apart with a lip clearance angle of approximately 12º. Twist drills have two angled cutting edges. ![]() The major reasons are found in the construction of the twist drill. The design and cutting characteristics of the standard twist drill, although efficient, are not well suited for precision machining. The most common cutting tool for drilling is the twist drill. ![]() They work well in assembly tools, inspection tools, and similar devices that require precise alignment and location of cylindrical parts. Drill bushings serve three purposes: they locate, guide, and support the cutting tool.Īlthough they serve mainly as guides for cutting tools, drill bushings also have other uses. They act as precision guiding devices for drills, reamers, taps, counterbores, and similar shank-mounted cutting tools. What is a Drill Bushing? What is a Drill Bushing?ĭrill bushings are a major element in most of today’s drill jigs. Customized & Special-Sized Drill Bushings.Alternative Materials for Drill Bushings.If you know which drill bushing details and information you are searching for in this guide, select the topic below to navigate to that section: Information in this guide is adapted from the Carr Lane Mfg. provides detiled information about the various applications, installation methods, and features of the different types of drill bushings. This Drill Bushing Guide from Carr Lane Mfg. ![]()
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