Machinery's Handbook, 31st Edition
2732
SHAFT ALIGNMENT
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Fig. 1b. Interpreting Dial Indicator Readings for Indicator Arrangement 1 Indicators are shown in the reading position. Solid lines represent the desired location for the dashed lines (movable unit). The plus, minus, and zero readings on the indicators are represented by one of these nine scenarios. Depending on the magnitude of the variables, the generic graph gives a mental picture of what the formulas should yield. Example 1(a), Vertical Alignment: Calculate the necessary shims for a pump and motor alignment where dimensions are A = 4 inches, B = 6.5 inches, and C = 18 inches. The two indicator dials read r = minus ( − ) 0.014 inch and f = plus (+) 0.021 inch respectively. Solution: The lower left block in Fig. 1b corresponds to a negative rim reading and a pos itive face reading. The figure indicates that both the front and rear feet will require shims, and that the rear feet will require more shims than the front feet. Shims on front and rear feet will be as follows:
A f B
A f C
! ! #
! ! #
R r
F r
2 = − + = − −
2 = − + = − −
. 2 0014
. 4 0021 65 . #
. 2 0014
. 4 0021 18 #
+
+
. . 0 007 0 034125 0041 .
. . 0007 00945 0102 . inch
inch = + = The calculations indicate that 0.041 inch of shims is required under both front feet, and 0.102 inch of shims is required under both rear feet. = + = Example 1(b), Horizontal Alignment: Fig. 1a. shows the indicators in the reading position for horizontal alignment, if the figure is thought of as a view looking down at the motor from the top. Assuming the same data obtained in the previous example, the two indicator dials read r = minus ( − ) 0.014 inch and f = plus (+) 0.021 inch respectively. Calculate the necessary horizontal movement required to align the motor to the pump. Solution: The equations adjacent to Fig. 1a apply, as in the previous example. The dimensions B and C in Fig. 1a are the respective distances from the rim indicator path on the coupling to the locations at the front and rear of the motor, not necessarily the feet, where the horizontal adjustments will be made. These locations could be the front and rear jackbolts, or they could be magnetic base monitoring indicators placed conveniently near the front and rear feet, as discussed previously with respect to Fig. 14. The diagram in the lower left corner of Fig. 1b indicates the direction of the move when the figure is viewed as if looking at the motor from the top. If B and C are 6.5 and 18 inches, respectively, then the equations indicate that the front and rear of the motor must be moved in the same direction, +0.041 inch and +0.102 inch respectively, to attain alignment.
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