Twist Measurement By Microscope

A microscope having a rotating stage what its periphery graduated in degrees can be used to measure the twist angle and the yarn diameter and enable the turn per inch to be derived.After micrometer eyepiece is employed and it is first calibrated against a stage micrometer.With the stage set a zero degrees the yarn,mounted in a suitable holder,is brought into focus and the moving hairline of the eyepiece brought into line with the yarn axis.The stage is now rotated until the hair line is tangential to the helix formed by the twisted fibers on the yarn surface.The angle through which the stage has been rotated is then recorded. The yarn diameter is measured in terms of eyepiece divisions and then converted to thousands of an inch.At this point the yarn diameter d is known and also the twist angleThe length of yarn occupied by one turn of twist is therefore given by

A number of observation will,of course,be taken since both the twist angle and the yarn diameter will very from point to point along the yarn.Twist determination by means of some from of twist counter is precise only for plied or cabled yarns.For single yarns an accurate determination is almost out of the question by this means.Certainly no adequate idea of twist contraction in this latter case is possible.