Sunday, 20 September 2020
MECHANICAL INSTRUMENTS

Dial indicators

To determine geometrical errors such as roundness, taper etc. Determination of errors caused in surface position such as alignment, parallelism, flatness, etc. Indicator used for measuring the deformation in compression or tension testing of components.

Dial indicator

It is used in measuring devices such as bore gauges, dial depth gauges, diameter gauges, etc. It is also used as comparator for comparing distance between limits of narrow size.

Classifications of Dial indicators

Dial indicators are mainly classified into two groups they are.

  • Sector type dial indicator
  • Circular type dials indicators.

Sector type dial indicator:

The sector type dial indicators are not commonly used as compared to circular type, due to its limited range.

Circular types dial indicators:

The circular type dial indicators are mainly two types they are based on the required applications.

Dial indicators

Plunger type dial indicator

  • Back plunger
  • Plunger parallel to plane of dial

Lever type dial indicator

Working Mechanism of dial indicator

Dial indicator is consists of a plunger which slides in its own bearings and carries a rack which is accurately meshes with a pinion. Pin attachment in plunger is provided to prevent it from rotation about its own axis.

A light coiled spring is attached to keep the plunger in its normal or extended position.

Mechanism of dial Indicator

  • A small movement in the point of contact causes the rack to move, which is in turn and rotate the pinion meshed to it.
  • Spindle of the pinion carries a gear which is meshes with pinion.
  • The pinions are magnifies the movement with each other.
  • The gear which meshes with a third pinion it is mounted on the spindle having indicator pointer.
  • The magnification is further enlarged according to the length of the pointer.
  • The overall magnification can be measured by the distance between the divisions of the scale and dividing this by the equivalent movement of the plunger.
  • A light spring is provided to take up the backlash is attached to the gear which is meshed with pinion.

Advantages of dial indicators

  1. Dial indicators are easily used by an unskilled.
  2. In mass production these are suitable for precision dimension control.
  3. Low and uniform contact pressure is applied on the work piece.
  4. It is portable, easy to handle and can be set very quickly.
  5. It is less costly comparatively.
  6. It detects the small dimensional variations that are beyond the range of conventional gauge.
  7. It is eliminates the undesired human errors while taking references.
  8. It requires less time and avoids the necessity of using different inspections and expensive setups.