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The keyseats in the shaft and the hub are designed so that exactly one-half of the height of the key is bearing on the side of the shaft keyseat and the other half on the side of the hub keyseat. Figure 11–2 shows the resulting geometry. The dis-tance Yis the radial distance from the theoretical top of the shaft, before the keyseat is machined, to the top edge of the finished keyseat to produce a keyseat depth of exactly H/2. To assist in machining and inspecting the shaft or the hub, the dimensions Sand Tcan be computed and shown on the part drawings. The equations are given in Figure 11–2. Tabulated values of Y, S,and Tare available in References 7 and 9.As discussed later in Chapter 12, keyseats in shafts are usually machined with either an end mill or a circular milling cutter, producing the profile or sled runner keyseat, respectively (refer to Figure 12–6). In general practice, the keyseats and keys are left with essentially square ends and edges. But radiused keyseats and chamfered keys can be used to reduce the stress concentrations. Table 11–2 shows suggested values from ANSI Standard B17.1.As alternates to the use of parallel keys, taper keys, gib head keys, pin keys, and Woodruff keys can be used to pro-vide special features of installation or operation. Figure 11–3 shows the general geometry of these types of keys.Taper Keys and Gib Head KeysTaper keysare designed to be inserted from the end of the shaft after the hub is in position rather than installing the key first and then sliding the hub over the key as with paral-lel keys. The taper extends over at least the length of the hub, and the height, H,measured at the end of the hub, is the same as for the parallel key. The taper is typically 1/8 in per foot. Note that this design gives a smaller bearing area on the sides of the key, and the bearing stress must be checked.The gib head key[Figure 11–3(c)] has a tapered geometry inside the hub that is the same as that of the plain taper key. But the extended head provides the means of extracting the key from the same end at which it was installed. This is very desir-able if the opposite end is not accessible to drive the key out.Pin KeysThe pin key,shown in Figure 11–3(d), is a cylindrical pin placed in a cylindrical groove in the shaft and hub. Lower stress concentration factors result from this design as com-pared with parallel or taper keys. A close fit between the pin FIGURE 11–1 Parallel keys. (Source for (d): Driv-Lok, Inc., Sycamore, IL)Key(d) Commercially available keys