Machinery's Handbook, 31st Edition
2748 SHAFT ALIGNMENT arrangement used matches the arrangement illustrated in Fig. 14a. In this problem the solution is obtained by using the same equations as were used to obtain the solution of Fig. 14a, adapted slightly to deal with the additional feet. Shim calculations for motor to pump alignment when the motor has more than four feet are performed in the same manner as the examples previously used. However, care must be used in determining the dimensions used in the equations. As in all the previous examples, the horizontal dimensions are measured from the location of the rim indicator. Distances to motor feet to the right of the rim indicator are assigned positive values, and distances measured to feet that are to the left of the rim indicator are assigned negative values in the formulas. The revised equations for this arrangement are shown beside Fig. 17. In the equations, S F is the shim requirement at foot F, S F 1 is the shim requirement at foot F1, etc.
f
F
r 2
h
^
−
! ! # = − + −
S
A
F
1
f
F
A
r 2 r 2 r 2
h
^
A −
! ! # = − + −
S
r
f
1
F
2
A f F A f F A f R
! ! # = − + −
S
R
F2
F1
2
F
F
F3
R
3
Fig. 17. Shaft Alignment When More than Four Feet are Involved Dimensions are measured from the path of the rim indicator. Dimensions to locations left of the rim indicator enter the equa tions as minus ( − ) values, and dimension to the right of the rim in- dicator enter the equations as positive (+) quantities.
! ! # = − + −
S
3
F
r 2
! ! #
S
= − + −
R
Example: Calculate the shims necessary for a pump and motor alignment where dimen sions are A = 4.5 inches, F = 22.0 inches, F 1 = 10.0 inches, F 2 = 8.0 inches, F 3 = 24.0 inches, and R = 46.0 inches. The two indicator dials read r = minus ( − )0.054 inch and f =
plus (+)0.032 inch, respectively. Solution, Vertical Alignment: . r f F ! ! # = − + − − = − − ^ h
. 45 0 032 22 0 027 0 156 0 183 . . . . # − = + = ^ h
2 0054
inch
S
+ −
2
A
F
1
. 45 0 032 10 0 027 0 071 0 098 . . . . # − = + = ^ h
f
F
. 2 0054
r 2 r 2 r 2
h
^
−
. 2 0054 . 2 0054 = − −
! ! # = − + −
inch
S
+ −
A
1
F
2
A f F A f F
. 45 0032 8 0027 0156 0030 . . . . # + − = + − ^ = − h
. 2 0054 A f R 3 ! ! # = − + − = − − ! ! # = − + − = − − ! ! # = − + − = − − r 2
inch
S
2
F
. 45 0 032 24 0 027 0 171 0 144 . . . . # + − = + − ^ = − h
inch
S
3
F
. 45 0 032 46 0 027 0 327 0 300 . . . . # = + − ^ = − h
inch
S
+ −
R
The calculations show that more shims are required under the two pairs of front feet, F and F 1, and need to be reduced for the other three pairs of rear feet. The top left figure in Fig. 14b (negative rim and positive face indicator readings) confirms that the numerical solution appears reasonable. Solution, Horizontal Alignment: The horizontal alignment solution follows the same procedure as the vertical solution above, and will use the same equations if the indicator set up shown in Fig. 17 is used. The dimensions F , F 1, F 2, F 3, and R are the distances from the rim indictor path to the respective locations where the move occurs, whether it be the location of the hold-down bolts, or another location where a monitoring dial indicator is mounted. See Solution for Horizontal Alignment on page 2729 for additional information on this subject.
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