10
HOW WE PROCEED TO DETERMINE THE VALUE OF
THE AVERAGE DIAMETER WITH ARCHIMEDE HR?
When you want to minimize the problem of circularity error, it’s useful to divide the
cylinder circumference in up to 12 arcs of 30°. On each arc is then taken the diameter
measurement, to obtain the value of the Average Diameter.
In case of measurement of a very irregular or deformed cylinder, the value of the average
diameter calculated by Archimede may not match with the value of the diameter
obtained with a two points measuring instrument; that unlike Archimede cannot detect
circularity errors due to a number of deformation lobes greater than 2 (the case of an
irregular ellipse).
When we use a micrometric gauge, a caliper or bore gauge for inner diameters, we are
using a two points measuring instruments. Such instruments are unable to detect the
circularity error in case of parts which have an odd number of lobes (3 or 5 lobes), also
if different angular position’s measurements are taken. With the two points measuring
instruments it is possible to estimate the circularity error only in the case of parts which
have an even number of deformation lobes (ellipses).
