A floating carriage micrometer, sometimes referred to as an effective diameter measuring micrometer, is an instrument that is used for accurate measurement of ‘thread plug gauges’. Gauge dimensions such as outside diameter, pitch diameter, and root diameter are measured with the help of this instrument. All these dimensions have a vital role in thread plug gauges, since the accuracy and interchangeability of the component depend on the gauges used. To reduce the effect of slight errors in the micrometer screws and measuring faces, this micrometer is basically used as a comparator. Figure1 illustrates a floating carriage micrometer.
Fig.1 Floating Carriage Micrometer
The carriage has a micrometer with a fixed spindle on one side and a movable spindle with the micrometer on the other side. The carriage moves on a finely ground ‘V’ guide way or an antifriction guide way to facilitate movement in a direction parallel to the axis of the plug gauge mounted between the centres.
The micrometer has a non-rotary spindle with a least count of up to 0.001 or 0.002 mm. The instrument is very useful for thread plug gauge manufacturers, in gauge calibration laboratories (established under NABL accreditation), and in standard rooms where in-house gauge calibration is carried out.