Instrumental methods for determining the centers of holes

The necessity of measuring the center distance between small holes (0.5 to 3 mm diameter) often arises in many industries, including those manufacturing watches, optical, mechanical , and electronic instruments. At presenl such measurements are made on universal or toolmaker's microscopes. The accuracy of measurement is l imited by the accuracy with which the center of the hole is determined visually. Investigations [1, 2] have shown that the error in determining the center of the hole mainly depends on random errors in aligning the axis of the eyepiece with the axis of the hole. The error is usually 5 to 8 g. It is, therefore, very important to develop methods and devices for semiautomatic or automatic al ignment of the optical system with the center of the hole.