How to Measure the Inner Dimension of a Ring Gauge with a Universal Toolmaker's Microscope
Measurement adopts the contact method. Generally, a probe with a diameter of several millimeters is used to contact the inner wall of the ring gauge under test. Thanks to the small diameter of the probe, point contact between the probe and the workpiece can be guaranteed. During measurement, when the probe is positioned at points A and B along the diameter direction of the ring gauge under test, take two instrument readings a and b. The inner diameter of the ring gauge is calculated by: D=(b-a)+d. Where: D - inner diameter of the tested ring gauge; b,a - two readings from the instrument; d - diameter of the instrument probe.
The optical sensitive lever must be used with the 3× objective lens. Three pairs of double reticle lines will not be visible if other objective lenses are selected. Before measurement, install the 3× objective lens on the main microscope of the universal toolmaker's microscope. Fit the optical sensitive lever onto the lower end of the 3× objective lens, push the optical sensitive lever upward, and secure it with a rotating fixing ring. Place the tested ring gauge at the center of the worktable without any movement to avoid measurement errors. Lower the bridge frame, insert the probe of the optical sensitive lever into the bore of the tested ring gauge, then adjust the longitudinal and transverse slides of the instrument so that the probe contacts the inner wall of the ring bore and lies on the bore's diameter. The sign for proper positioning is that, when adjusting the transverse slide, the longitudinal reading reaches a turning point (maximum or minimum value). Keep the transverse reading unchanged, slightly move the longitudinal slide until three pairs of double reticle lines in the eyepiece symmetrically enclose the solid line of the crosshair reticle, and record the primary longitudinal reading a1. Then rotate the force-direction ring to reverse the measuring force direction. Move the slide to the opposite side of the tested ring gauge so that the probe contacts the bore wall along the bore diameter, adjust the probe to the vertical position, and record the secondary longitudinal reading b1.
The measurement principle of bore measurement by contact method is D=(b-a)+d, which is used to calculate the final result. The diameter d of the optical sensitive lever probe is marked on the side face of the lever.
Example: Measure a φ20 mm ring gauge. Given the diameter d of the optical sensitive lever probe = 3.10749 mm, the primary reading = 81.16569 mm, the secondary reading = 98.15862 mm. The inner diameter of the ring gauge is: D=(98.15862-81.16569)+3.10749=20.10042(mm).
