Machinery's Handbook, 31st Edition
2730
SHAFT ALIGNMENT
C'
B'
EAST
Fixed Unit
A
WEST
B
C
Fig. 14. Top View of Motor from Fig. 13 Side to Side Adjustment Using Jackbolts: Avoid using jackbolts that are longer than nec essary. Make sure internal and external threads are clean and lubricated enough to be functional. Then, if heavy resistance is encountered when adjusting jackbolts, it indicates a mechanically-bound condition, not a rusty jackbolt thread. Before advancing jackbolts on one side of the movable unit, back off the jackbolts on the opposite side about 1 1 ⁄ 2 turns to provide enough space to make the movement without creating a mechanical bind. Jackbolts should not be left in a “bind” against the movable unit to assist in keeping the movable unit in alignment. After alignment is complete, the jackbolts should be removed and stored for future use. This action will prevent jackbolt corrosion, and leave the jack- bolt nuts vacant to receive a tap and lubrication, prior to being used again. On movable units outfitted with jackbolts, one complete (360 ° ) turn of a jackbolt will advance the thread an amount equal to the pitch of the screw thread. For inch-threaded screws, pitch equals 1 divided by the number of threads per inch (1 ÷ TPI). The axial travel per head flat is the pitch divided by the number of flats on the bolt head. Example: A jackbolt has a 1 ⁄ 2 -13 thread. Find the axial travel per revolution and per flat for square-head and hex-head bolts. The thread has 13 threads per inch. . . . 13 1 00769 4 13 4 1 # = 1 1 00192 00128 6 h h Example: A motor needs to be moved 0.064 inch east at the front jackbolt and 0.091 east at the rear. The square-head jackbolts are 5 ⁄ 8 -11. How many turns of the front and rear jackbolts are need to bring the unit into approximate alignment? onefull turn of jackbolt 11 1 0.0909 inch full turns at front jackbolt 0.0909 0.064 0.7040 4 3 turn or 3 flats full turns at rear jackbolt 0.0909 0.091 1.0011turn 1turn or 4 flats . . = = = = = = 13 6 1 # advance per revolution (full turn) of bolt inch advanceper flat (1/4 turn) of square head bolt advance per flat (1/6 turn) of hex head bolt − inch inch # # = = = − = = = = = ^ ^ TPI TPI TPI 1
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