The keyseats in the shaft and the hub are designed so

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 Y is 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 S and T can be computed and shown on the part
drawings. The equations are given in Figure 11–2. Tabulated
values of Y, S, and T are 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 Keys
Taper keys are 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 Keys
The 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