Page 71 - CITS - Fitter - Trade Theory

FITTER - CITS

1 Plunger or lever mechanism: This mechanism translates the linear motion of the stylus into rotational motion,
which is then indicated on the dial face. In plunger-type indicators, the stylus is connected to a spring-loaded
plunger that moves linearly against a spring. In lever-type indicators, the stylus is connected to a lever that
pivots as it makes contact with the object.

2 Spring: In plunger-type indicators, a spring is used to apply a constant force to the plunger, ensuring consistent
measurements by keeping the stylus in contact with the object.
3 Dial face: The dial face is typically a circular disc marked with graduations that represent units of measurement,
such as thousandths of an inch or hundredths of a millimetre. The indicator needle moves along this dial to
indicate the measurement being taken.
4 Indicator needle or pointer: The indicator needle is attached to the plunger or lever mechanism and moves
across the dial face to indicate the measurement being taken. It typically has a fine point for precise readings.
5 Bezel and crystal: The bezel is the outer ring that holds the crystal or glass covering the dial face, protecting
it from damage and contamination while allowing the user to see the measurements clearly.
Principal
The working system of dial test indicator is the principal of Rack & Pinion.
Least count of dial test indicator

In indicator rake 25mm length with 50teeth fitted on spindle. i.e when one teeth, i.e when one teeth of rake moves
upward, rake moves 1/2mm. Pinion 10teeth meshes with it & gear ‘B’ is fitted on 10teeth pinion axis. Pinion ‘C’
having 15teeth meshes with gear ‘B’ having 75teeth No. of revolution=Driver/Driven =50/10×75/15=25.
50teeth of rake=25 revolution Moving on 1teeth=25×1/50=1/2revolution. If dial is divided into 100equal part’s, the
half dial=50part’s =1/2×1/50=1/100mm or L.C=0.01mm
Care and maintenance of dial test indicator
• Keep the dial test indicator spindle and point clean using a soft cloth.
• Store the dial test indicator in a safe, dry place and cover them to keep the dust and moisture out.
• Do the dial test indicator under gaging conditions at intervals during the operating day

Bore gauge

• Introduction of bore gauge
A bore gauge is an essential precision measuring instrument utilized across various industries for accurately
measuring the internal diameter of holes, cylinders, or bores. Engineered with precision and accuracy in mind,
bore gauges provide crucial data for quality control, manufacturing processes, and maintenance procedures.
Bore gauges typically consist of a main body with a measuring head at one end and a dial indicator or digital
readout at the other. The measuring head features contact points or anvils that make contact with the inner
surface of the bore being measured. As the gauge is inserted into the bore, the contact points expand outward,
and the resulting expansion is measured by the dial indicator or digital readout. This measurement provides an
accurate representation of the bore diameter.

• Types of bore gauge
Bore gauges come in various types to accommodate different applications and bore sizes. Some common types
include:

1 Two-point bore gauges: These gauges have two contact points and are suitable for measuring simple bores
with consistent diameters.
2 Three-point bore gauges: Featuring three contact points, these gauges offer more stability and accuracy,
making them ideal for measuring bores with uneven surfaces or out-of-roundness.
3 Telescoping bore gauges: Consisting of multiple telescoping segments, these gauges are adjustable and
versatile, allowing for measurements of bores with varying diameters.

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CITS : CG & M - Fitter - Lesson 10