Bench Centres (Metrology)

2.14.
Bench centre consists of a rigid cast iron base made from close grained cast iron having
minimum hardness of 180 HB (free from distortion, porosity and other casting defects). The base
is provided with suitable T-solts for the attachment of the
centre holders. The centre holders can be located in any
desired position. The male or female centres are adjus-
table and can be locked in any position along the ground
vees of the centre holder. These are used for checking
eccentricity of rotary components between centres.
These are available with heights of centres 125,
160, 200, 250 and 300 mm. For easy loading and unload-
ing, one of the centre is spring loaded. The distance
between the centres may vary from 500 mm to 1500 mm depending on the height of the centres.
The coaxiality of centres and parallelism of axis of centres with respect to guideways should be
ensured within close tolerances.
The permissible deviations in parallelism of the axis of centres with respect to guideways,
as per IS: 1980—1978 are 0.01 mm per 300 mm, and 0.015 mm/300 mm respectively leaning towards
the free end of mandrel for centre heights of 125—160 mm and 200—300 mm respectively. The
corresponding permissible errors in coaxiality of centres are 0.01 mm and 0.015 mm respectively
over any length of 300 mm.