Machinery's Handbook, 31st Edition
2724 SHAFT ALIGNMENT A heavy duty version of the rock-a-bye method is to have all the hold-down bolts tight and then loosen them one at a time while monitoring the indicators.
Profile View
Overhead View
MOTOR BASE
Fig. 6. Rim Indicator Mounted to Test for Soft Feet Fig. 6 shows a profile view (left) and overhead view (right) of the motor previously shown. In this figure, the indicator illustrated is mounted exactly as the rim indicator will later be mounted for checking alignment, and any soft leg activity will register the same as in the line-up process. Once a motor gets a clean bill of health from this soft foot check, it is safe to proceed with the normal procedures of motor alignment. Mount the indicators in the most convenient manner that will apply to the problem at hand and select the proper formula as discussed in the material that follows. Be sure all the bolts are tight before mak ing the first (vertical) indicator reading Other Mounting Issues: Any combination of the mounting conditions illustrated in Fig. 7 will produce soft motor feet, even if the motor feet are machined properly. The motor, base, or shims will need alterations to circumvent the illustrated problems. De- pending on the magnitude of the angle in a problem of this sort, wedge-shaped shims or machine work on the motor or the base may be required. Sometimes on relatively unimportant equipment, it is permissible to simply fold shims in various thicknesses to take up the slack. This method should not be used as common practice; but as an emergency measure, it is very effective.
Fig. 7. Mounting Conditions That Produce Soft Motor Feet. Mounting Dial Indicators, Perpendicular versus Otherwise.— When indicators are mounted to get a rim reading on a coupling, the indicator stem should be set to aim straight through the center of the shaft, and at a perpendicular to the axis of the shaft. This center shot at a perpendicular does not have to be absolutely perfect, but it should be close enough so that a closer than casual visual inspection can find no flaw. This is close enough for practical purposes. A
B
D
C
Fig. 8. Indicator Stem Orientation, Correct at A and B, Incorrect at C and D
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