Improved parallelism measurement using a laser interferometer

The authors discuss an improved method for obtaining parallelism measurements of two straight bars in a plane, considering the specific problem of making two vertical surfaces parallel to each other to within 0.00005 of an inch over a 50 inch length. The authors compare the existing method of using dial indicators and a slider with that of using a laser interferometer, cable and pulley system, and a microcomputer. Possible errors this system may generate and solutions to help minimize them are presented. The procedure presented will help to minimize errors due to the operator such as 'reading between the lines' on an indicator and hand applied pressure. These methods allow improved parallelism resolution over that obtainable with the indicator.<>