Cone Keys.—These are sometimes fitted to pulleys, and are shown in fig. 32, page 38. In this case the eye of the pulley is tapered and is larger than the shaft. The space between the shaft and the boss of the pulley is filled with three saddle or cone keys. These keys are made of cast iron and are all cast together, and before being divided the casting is bored to fit the shaft and turned to fit the eye of the pulley. By this arrangement of keys the same pulley may be fixed on shafts of different diameters by using keys of different thicknesses; also the pulley may be bored out large enough to pass over any boss which may be forged on the shaft.
Proportions of Keys.—The following rules are taken from Unwin's 'Machine Design,' pp. 142-43.
| Diameter of eye of wheel, or boss of shaft | = d. |
| Width of key | = 3⁄4d + 1⁄8. |
| Mean thickness of sunk key | = 1⁄8d + 1⁄8. |
| ” key on flat | = 1⁄16d + 1⁄16. |
The following table gives dimensions agreeing with average practice.
Dimensions of Keys.
| D | = | diameter of shaft. |
| B | = | breadth of key. |
| T | = | thickness of sunk key. |
| T1 | = | thickness of flat key, also = thickness of saddle key. Taper of key 1⁄8 inch per foot of length, i.e. 1 in 96. |
| D | ¾ | 1 | 1¼ | 1½ | 1¾ | 2 | 2¼ | 2½ | 2¾ | 3 | 3½ |
|---|---|---|---|---|---|---|---|---|---|---|---|
| B | 5⁄16 | 3⁄8 | 7⁄16 | 1⁄2 | 9⁄16 | 5⁄8 | 11⁄16 | 11⁄16 | 3⁄4 | 7⁄8 | 1 |
| T | 1⁄4 | 1⁄4 | 1⁄4 | 5⁄16 | 5⁄16 | 5⁄16 | 3⁄8 | 3⁄8 | 3⁄8 | 7⁄16 | 1⁄2 |
| T1 | 3⁄16 | 3⁄16 | 3⁄16 | 3⁄16 | 1⁄4 | 1⁄4 | 1⁄4 | 5⁄16 | 5⁄16 | 5⁄16 | 3⁄8 |
| D | 4 | 4½ | 5 | 5½ | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| B | 11⁄8 | 11⁄4 | 13⁄8 | 11⁄2 | 15⁄8 | 17⁄8 | 21⁄8 | 23⁄8 | 25⁄8 | 27⁄8 | 31⁄8 |
| T | 1⁄2 | 9⁄16 | 5⁄8 | 11⁄16 | 3⁄4 | 13⁄16 | 15⁄16 | 1 | 11⁄16 | 13⁄16 | 11⁄4 |
| T1 | 7⁄16 | 1⁄2 | 1⁄2 | 9⁄16 | 5⁄8 | 11⁄16 | 3⁄4 | 7⁄8 | 15⁄16 | 11⁄16 | 11⁄8 |