Thursday, 22 October 2020
MECHANICAL INSTRUMENTS

Projection comparator

The Projection comparator is a measuring instrument. It is used for measuring the part of the shadow being on a screen, where it is a compared to a master drawing. The projection comparator method is suitable for complicated type shaped parts.

In any projection system, there are four essential elements such as.

  • Source of light
  • Condensing lens
  • Projection lens
  • Screen

The illumination required for any projector is a parallel beam of light, which can be achieved if the source of light is placed at the principle focus of the collimating lens.

projection Comparator

The collimating lens is to render the beam of light from point source parallel. The projection lens consists of a system of lenses, which form a real image on the screen of an object placed between it and collimator. The screen is generally transparent so that the image can be viewed from the opposite side.

Working of Projection comparator

The projection comparator instrument is especially suitable for

  • To measuring the gear hub cutter
  • Measurement of any complicated shapes
  • The tooth relief concentricity
  • The flute spacing
  • Measuring the helix angle in screw threads

The working of projection comparator illuminating system consists of a light source and a tungsten arc lamp. The glowing element in the lamp is a small cylinder of tungsten, which is heated by electron bombardment.

It is enclosed in a ventilated lamp house. Light is coming from the lamp passes to a system of lenses called achromatic condenser.

By using a single lens condenser, the image on the screen can be displayed in various colors. So as to get rid of them, each lens assembly is composed of two kinds of glasses.

The parallel beam of light from the condenser is then transmitted to the illumination mirror, which passes vertically upwards.