Autocollimator and tool makers micro scope

Autocollimator

  • The autocollimator is an optical instrument and is used to measure angular displacements with high accuracy of 0.2 seconds arc
  • It can also be used to measure the flatness of a large surface


Collimation of light

  • If a point source of light is placed at the focal point of convex lens ,parallel rays of light are reflected by the lens. This is known as collimation of light
  • A device with a lens suitable for causing light rays from a point source to become parallel is known as a collimator



Auto collimation of light

  • Auto collimation of light occurs when reflecting surface is used in conjunction with a collimation lens system
  • The collimation rays will be reflected back from the surface
  • These rays pass through lens ,and unless reflecting surface is perfectly tangential to the lens axis ,will be brought to a focus along side of the light source




Principle of the autocollimator

  • From the fig. The light in the form of parallel rays , is reflected from the surface of reflector
  • After re-entering the objective lens ,the light form an image of target wires in the same plane as the wire itself
  • The eyepiece incorporated in micrometer enables the observer to measure any angular displacement caused by misalignment at the reflector
Autocollimator accessories
    • Leveling base
    • Surface plate stand
    • Steel reflector
    • Mounted glass corner reflector
    • Steel cube reflector

Leveling base

  • It supports the autocollimator and enables it to be leveled to bring its axis parallel to the surface being measured
  • It incorporates spring loaded clamps and a circular bubble level
  • Three pads are included for use under the foot screws
  • There is no necessity to remove the autocollimator from the base after use as the autocollimator case is constructed to take both items

Surface plate stand
  • A multi purpose stand of heavy duty construction for general bench use ,comprises ground cast iron surface plate, column and bracket
  • The Autocollimator clamping bracket has independent clamping and rotational adjustments, enabling the bracket to be turned with out disturbing the height adjustment

Steel reflector

  • A reflector must be regarded as an integral part of any autocollimator system
  • Successful auto collimation requires a reflector of adequate flatness reflectivity and diameter
  • The faces are not perfectly parallel when the reflector is mounted at the back.

Mounted glass corner reflector

  • This is used in conjunction with a reflector carriage and mounted reflector for calibrating a surface plate
  • It enables several calibration lines to be traversed without the autocollimator being moved
  • Thereby saving setting–up time and making the subsequent correlation of reading easier

Steel cube reflector

  • It can be used as a general purpose reflector and for providing a 90ºangle stand in three planes for setting or checking perpendiculars

Autocollimator applications

  • To the measurement of straightness and flatness
  • Precise angular indexing in conjunction with polygons
  • Comparative measurement using master angles
  • Assessment of squareness and parallelism of components
  • The measurement of small linear dimensions

The toolmaker’s microscope

  • The toolmaker’s microscope has a table on which work piece is clamped
  • The table movements are controlled by micrometer
  • The light source is contained in the base
  • The work may be viewed directly as in the case of conventional microscopes or projected on screen


  • When looking into the eyepiece of this microscope two thin straight lines intersecting at the centre of the field may be seen on the glass at the focal plane
  • The microscope is focused to show a clear image of a magnified portion of work piece on a focal plane
  • To take the measurement ,one cross-line of the eyepiece is aligned with one end of the dimension and location of table is noted
  • The table is moved so that the same line in the eyepiece next aligned with the opposite end of the dimension and location of the table is again noted
  • The difference in the two readings is the desired measurement

Optical system of toolmaker’s microscope

  • The optical system with projection screen of toolmaker’s microscope is shown in fig.
  • The image of the work profile is focused by the objective lens system and passed through an inverting prism
  • To ensure that the projected image is oriented same as the object on the work stage


  • The projected light then picks up the image of a graticule which can be focused by a second lens system before passing through a right angled prism
  • Both images are then projected by the final lens ,of the reflecting mirror and on to the screen

Applications of toolmaker’s microscope

  • To measure the diameter of holes and distances between centres
  • Position of keyway with reference to centre of bore
  • Angles and pitch of threads
  • Gear tooth spacing

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