Machinery's Handbook, 31st Edition
706 CHECKING SHAFT CONDITIONS To check for taper, the shaft is supported in the V-block and the dial indicator is used to measure the maximum height over the shaft at various positions along its length, as shown in Fig. 4b, without turning the workpiece. Again, the shaft should be marked with the reading positions and values, and with the direction of the taper, and a written record should be made of the amount and direction of any taper discovered. Checking for a bent shaft requires that the shaft be clocked at the shoulder and at the far ther end, as shown in Fig. 4c. For a second check, the shaft is rotated only 90 ° or a quarter turn. When the recorded readings are compared with those from the ovality and taper checks, the three conditions can be distinguished. To detect a curved or bowed condition, the shaft should be suspended in two V-blocks with only about 1 ⁄ 8 inch of each end in each V. Alternatively, the shaft can be placed between centers. The shaft is then clocked at several points, as shown in Fig. 4d, but preferably not at those locations used for the ovality, taper, or crookedness checks. If the single element due to curvature is to be distinguished from the effects of ovality, taper, and crookedness, and its value assessed, great care must be taken to differentiate between the conditions detected by the measurements. Finally, the amount of eccentricity between one shaft diameter and another may be tested by the setup shown in Fig. 4e. With the indicator plunger in contact with the smaller diameter, close to the shoulder, the shaft is rotated in the V-block and the indicator needle position is monitored to find the maximum and minimum readings. Curvature, ovality, or crookedness conditions may tend to cancel each other, as shown in Fig. 5, and one or more of these degrees of defectiveness may add themselves to the true eccentricity readings, depending on their angular positions. Fig. 5a shows, for instance, how crookedness and ovality tend to cancel each other, and also shows their effect in falsifying the reading for eccentricity. As the same shaft is turned in the V-block to the position shown in Fig. 5b, the maximum curvature reading could tend to cancel or reduce the maximum eccentricity reading. Where maximum readings for ovality, curvature, or crookedness occur at the same angular position, their values should be subtracted from the eccentricity reading to arrive at a true picture of the shaft condition. Confirmation of eccentricity readings may be obtained by reversing the shaft in the V-block, as shown in Fig. 5c, and clocking the larger diameter of the shaft.
Maximum Eccentricity
Maximum Eccentricity
Maximum Ovality
Maximum Ovality
Maximum Crookedness
Maximum Curvature
Maximum Crookedness
Position a
Position b
c
Fig. 5. Out-of-Roundness—Lobing.— With the imposition of finer tolerances and the develop ment of improved measurement methods, it has become apparent that no hole, cylinder, or
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