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Difficulty: MediumMeasuring and Layout Tools

A mechanic is setting up a differential assembly and needs to measure the gear backlash between the ring gear and drive pinion to within thousandths of an inch. Which measuring instrument, typically secured to the housing with a rigid magnetic base, is designed to measure this minute linear movement?

  1. A
    Outside micrometer
  2. Dial indicatorAnswer
  3. C
    Depth micrometer
  4. D
    Inside caliper

Answer

Dial indicator
A dial indicator is specifically engineered to measure minute distances, runout, and endplay. When mounted on a magnetic base and positioned with its plunger against a ring gear tooth, rocking the gear translates the clearance into needle rotation on the dial, providing a direct reading in thousandths of an inch.

Step-by-Step Solution

1
Identify the type of measurement required by the task.
The task requires measuring gear backlash, which is the tiny linear movement or free-play between two meshed gears, measured in thousandths of an inch.
Backlash requires an instrument capable of measuring positional deflection while a component is gently rocked back and forth.
2
Evaluate the mounting and functional capabilities of shop measuring tools.
A dial indicator with a magnetic base can be firmly clamped to the differential carrier housing with its plunger positioned perpendicular to a ring gear tooth.
Rigid mounting prevents base movement so that only the mechanical travel of the gear tooth is transferred to the indicator needle.
3
Select the tool that directly displays small linear displacements.
The dial indicator directly registers deflections as small as 0.001 inches (or 0.0001 inches) on its graduated dial face.
Micrometers and transfer calipers measure static physical dimensions rather than relative linear displacement.

Key Concept

Measuring mechanical play, runout, and backlash using a dial indicator
Estimated Time:1m 0s
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Topics

Measuring and Layout Tools

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