Machinery's Handbook, 31st Edition
SHAFT ALIGNMENT 2731 Practical Rim and Face Dial IndicatorArrangements forShaftAlignment This phase of millwright/machinist work is usually referred to as motor-to-pump align ment. The true objective is to correctly align the axis of one shaft to the axis of another by any of a rather wide range of dial indicator mountings, depending on a myriad of varying situations. These motor to pump scenarios can be duplicated on almost any shaft that is axially in close proximity to another shaft that has to share a common axis. Addressed here is standard rim and face pump alignment. There are sixteen indicator arrangements to select from in this rim and face section. Units are aligned as closely as possible with a straight edge before using the dial indica- tors. At the first indicator reading, a neat sketch of the scenario is made, along with a care - fully measured dimensioning schedule such as that shown in Fig. 1a. Based on indicator readings, select the applicable block from the second illustration, Fig. 1b, that matches the current plus or minus ( ± ) indicator reading. The dashed lines in Fig. 1b represent the cen- terline of the movable unit shaft. The two heavy round dots on the dashed lines (to the right of the couplings) represent points directly above or below the movable unit shim locations, and indicate that the movable unit must be raised or lowered at that location. The diagrams will help clarify the results of the shim calculations made using the appropriate formulas. Be certain to use minus signs any time they are called for in the formulas. Note: In all the rim and face formats that follow, the axial location of the rim indicator always dictates the beginning point of the dimensions that are used in the various formu- las. Also, the dial indicator arrangements in Fig. 1a through Fig. 16a are shown in the reading position , after having been zeroed at the position 180 ° opposite that shown and then rotated into the position shown. 1st Arrangement.— Fig. 1a illustrates the most universally accepted method of mounting dial indicators for shaft alignment, and it is also the same arrangement that was used in the preceding example, illustrated by Fig. 13 and Fig. 14. When a reading of the rim and face indicators has been made, find the diagram in Fig. 1b that corresponds to the signs (positive or negative) of the readings obtained (positive rim value and negative face value, for example). The appropriate diagram will provide a visual clue to the meaning of the indicator readings, and indicate the direction that the motor feet must be moved to obtain alignment of the movable shaft with the fixed shaft. Finally, use the equations adjacent to Fig. 1a to calculate the exact thickness of shims that need to be added or removed at each foot.
A f B A f C
2 2 ! ! # ! ! #
A
F r R r
= − + = − +
f
r
F
R
B
C
Fig. 1a. Dial Indicator Arrangement 1
In the rim and face format in Fig. 1a, r and f represent the values of the rim and face indicators in their reading positions. The F and R below the motor are the front and rear feet, corresponding to the F and R values in the formulas that represent the needed plus or minus ( ± ) shim packs. The formulas adjacent to Fig. 1a, are used to calculate the necessary addition or subtraction of shims required on the front or rear feet.
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