Keyways are grooves of different shapes cut along the axis of the cylindrical surface of shafts, into which keys are fitted to provide a positive method of locating and driving members on the shafts. A keyway is also machined in the mounted member to receive the key.
The type of key and corresponding keyway to be used depends upon the class of work for which it is intended. The most commonly used types of keys are the Woodruff key, the square-ends machine key, and the round-end machine key (Figure 4-35).
The Woodruff keys are semicylindrical in shape and are manufactured in various diameters and widths. The circular side of the key is seated into a keyway which is milled in the shaft. The upper portion fits into a slot in a mating part, such as a pulley or gear. The Woodruff key slot milling cutter (Figure 4-36) must have the same diameter as that of the key
Figure 4-35. Woodruff key slot
Woodruff key sizes are designated by a code number in which the last two digits indicate the diameter of the key in eights of an inch, and the digits preceding the last two digits give the width of the key would be 4/8 or ½ inch in diameter and 2/32 or 1/16 inch wide, while a number 1012 Woodruff key would be 12/8 or 1 ½ inches in diameter and 10/32 or 5/16 inch wide. Table 8-4 in Appendix A lists Woodruff keys commonly used and pertinent information applicable to their machining.
For proper assembly of the keyed members to be made, a clearance is required between the top surface of the key and the keyway of the board. This clearance may be from a minimum of 0.002 inch to a maximum of 0.005 to 0.001 inch wider than the keyway.
Milling Cutters Used for Milling Keyways
Shaft keyways for Woodruff keys are milled with Woodruff keyslot milling cutters (Figure 4-35). The Woodruff keyslot milling cutters are numbered by the same system employed for identifying Woodruff keys, Thus, a number 204 Woodruff keyslot cutter has the proper diameter and width for milling a keyway to fit a number 204 Woodruff key.
Square-end keyways can be cut with a plain milling cutter or side milling cutter of the proper width for the key.
Round-end keyways must be milled with end milling cutters (Figure 4-37) so that the rounded end or ends of the key may fit the ends of the keyway. The cutter should be equal in diameter to the width of the key.
Alignment of Milling Cutters
When milling keyways. the shaft may be supported in the vise or chuck, mounted between centers. or clamped to the milling machine table. The cutter must be set centrally with the axis of the workpiece. This alignment is accomplished by using one of the following methods:
When using a Woodruff keyslot milling cutter, the shaft should be positioned so that the side of the cutter is tangential to the circumference of the shaft. This is done by moving the shaft transversely to a point that permits the workpiece to touch the cutter side teeth. At this point the graduated dial on the cross feed is locked and the milling machine table is lowered. Then, using the cross feed graduated dial as a guide, the shaft is moved transversely a distance equal to the radius of the shaft plus 1/2 the width of the cutter.
End mills may be aligned centrally by first causing the workpiece to contact the periphery of the cutter, then proceeding as in the paragraph above.
Milling Woodruff Key Slot
The milling of a Woodruff keyslot is relatively simple since the proper sized cutter has the same diameter and thickness as the key. With the milling cutter located over the position in which the keyway is to be cut, the workpiece should be moved up into the cutter until you obtain the desired keyseat depth. Refer to Table 8-4 in Appendix A for correct depth of keyslot cut for standard Woodruff key sizes. The work may be held in a vise. chuck. between centers. or clamped to the milling machine table. Depending on its size, the cutter is held in an arbor or in a spring collet or drill chuck that has been mounted in the spindle of the milling machine.
Figure 4-36. Keyway milling.
Square-End machine Key
Square-end machine keys are square or rectangular in section and several times as long as they are wide. For the purpose of interchangeability and standardization, these keys are usually proportioned with relation to the shaft diameter in the following method:
Key width equals approximately one-quarter of the shaft diameter.
Key thickness for rectangular section keys (flat keys) equals approximately 1/6 of the shaft diameter.
Minimum length of the key equals 1 1/2 times the shaft diameter.
Depth of the keyway for square section keys is 1/2 the width of the key.
Depth of the keyway for rectangular section keys (flat keys) is 1/2 the thickness of the key,
Table 8-5 in Appendix A lists common sizes for square-end machine keys. The length of each key is not included because the key may be of any length as long as it equals at least 1 1/2 times the shaft diameter.
Round-end machine keys (Figure 4-35). The round-ends machine keys are square in section with either one or both ends rounded off. These keys are the same as square-ends machine keys in measurements (see Table 8-5 in Appendix A).
Milling Keyslot for Square-End Machine Key
The workpiece should be properly mounted, the cutter centrally located, and the workpiece raised until the milling cutter teeth come in contact with the workpiece. At this point, the graduated dial on the vertical feed is locked and the workpiece moved longitudinally to allow the cutter to clear the workpiece. The vertical hand feed screw is then used to raise the workpiece until the cutter obtains the total depth of cut. After this adjustment. the vertical adjustment control should be locked and the cut made by feeding the table longitudinally.
Milling Keyway for Round-End Machine Key
Rounded keyways are milled with an end milling cutter Of the proper diameter. As in the case of square-ends machine key keyways, the workpiece should be properly mounted and the cutter centrally located with respect to the shaft. The shaft or cutter is then positioned to permit the end of the cutter to tear a piece of thin paper held between the cutter and the workpiece. At this point the graduated feed dial should be locked and used as a guide for setting the cutter depth. The ends of the keyway should be well marked and the workpiece moved back and forth making several passes to eliminate error due to spring of the cutter.
Figure 4-37. Round-end key way.
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