 Previous Page 131.02
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Use and
Care of the Dial Indicator
Background Electricians use dial indicators to align couplings and measure shaft and bearing runout. Excessive shaft and bearing runout and misalignment between the driver and driven unit can cause bearing failure and increase operating noise, temperature, and vibration. Use of the dial indicator allows for quick and accurate measurements to 0.0001 inch or 0.001 inch, depending on the model used. The dial indicator is light and compact and can be carried easily to the jobsite.
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Click on image to enlarge. Dial Indicator on Rotor in Test Blocks |
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Parts of a
typical dial indicator
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Click on image
to enlarge. Dial Indicator |
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| Measuring
shaft radial runout Attach the magnetic base to the end of the motor, motor mount, deck, or V block as appropriate.
Mount the dial indicator on the tool post holder by sliding the shaft through the clamp and tightening the thumbscrew. Adjust the tool post holder to permit easy reading of the instrument face. Bring the sensor button into contact with the surface to be measured. Tilt the adjustable sensing arm to wipe across the surface being measured. The button should contact the shaft as close to the end as possible. Raise and lower the sensor button with the tool post thumbscrew to determine full travel of the indicator pointer. Leave the pointer at midtravel and zero the bezel by loosening the bezel clamp screw and turning the bezel until the zero on the dial face is under the pointer, then retighten the bezel clamp screw.
Rotate the shaft slowly. If the shaft is straight, the instrument pointer should remain at, or near, zero. Runout should not exceed 0.002 inch of total indicator reading unless otherwise specified on equipment drawings.
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Click on image to enlarge. Measuring Shaft Radial Runout
Click on image to enlarge. Closeup of Dial Indiator (Shaft Radial Runout) |
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| Record the measurement on the motor data sheet (mechanical). | Click on image to
enlarge. Typical Motor Data Sheet (Mechanical) |
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Measuring inner bearing ring face runout  |
The shaft must be clean and free of corrosion.
If the shaft has a groove or keyway, do NOT allow the sensor
to enter this recess because this may damage the sensor. The shaft must be turned to one
edge of the groove and then back around to the other edge.
