Squareness of X axis to Y axis is checked by placing a square on the center of the optical comparator table banked up against one of the stage vees. Face it to the right or left side. Place a magnetic base indicator on the face of the comparator near the chart ring. Lower the Y-axis to the bottom and place the tip of the indicator on the side of the square. Raise the Y-axis and check the squareness of the X axis in relation to the Y axis travel. It should be .0001” or less per inch (≤ .0006” for 6” travel). If adjustment is needed the knee bracket must be loosened and twisted to correct.

Squareness of Y axis to focus plane

Squareness of Y axis to focus plane is checked in the same manner as squareness of X axis to Y axis only with the face of the square facing forward or back. This should be .0005” per inch or less (≤ .003” for 6” travel). If this is not correct you would need to shim under the lower focus bearings to bring into spec.

X axis stage linear traveling accuracy

For this specification we use the formula ± (150+L/.02)µin. For a 10” travel optical comparator stage we would divide 10” by .02 to get 500 then add to it 150 for a ± total of 650 micro inches over 10” travel (±.00065”). The optical comparator stage is inspected using the 6” scale on the Acu-Rite master in the center of the stage. The deviation from the expected reading is recorded on the inspection sheet in micro inches (.000001”), a minus sign before the value indicates the measurement was under size. If corrections are needed a new comp. value can be entered into the optical comparator digital readout for the axis you are working on. Errors that are linear in nature are easily compensated for. If your readings are very non-linear it could indicate damage or looseness. The remarks section of the inspection sheet shows any error compensation set in the digital readout for that axis.

Y axis stage linear traveling accuracy is checked the same as X only with the master standing vertical on the stage.

ERP calibration counts

This value indicates the number of pulses recorded by the rotary encoder during calibration. The idea is to have a point of reference to use in the future if any errors or changes are needed to make the digital angle display more accurate. To re-calibrate the rotary encoder follow the instruction in the optical comparator manual and record the new value on the inspection sheet after a satisfactory value is achieved on the display.

ERP Repeatability

A check in this box indicates that the angle display is within ± 30 minutes of angle over a 360° rotation (±0.5°).

Related posts:

1. Optical comparator magnification
2. Optical comparators operating basics part 2