Locating plug for the centerlines of holes

A fixture useful in connection with a programmable coordinate measurement machine to determine the centerline of a threaded hole formed in a workpiece comprising:

• an elongated cylindrical member threaded at one end in a manner complimentary to the thread of the hole so that the end of the cylindrical member may be threadedly inserted into the hole with one end of the fixture extending beyond the surface of the hole;
• and
• a cylindrical counterbore formed on the centerline of the cylindrical member from the end opposite that which threads into the hole, whereby the fixture may be threaded into the hole, and a probe of a programmable coordinate measurement machine moved into the counterbore and brought into contact with three opposed points in the counterbore with three programmed motions so that the coordinate measurement machine can calculate the centerline of the counterbore and accordingly the centerline of the threaded hole.

The method of determining the centerline of a threaded hole formed in a workpiece, comprising:

• placing a fixture having a cylindrical section threaded to mate with the threads of the hole and an extending section formed with a counterbore concentric to the centerline of the cylindrical section into the hole by threading the cylindrical section into the hole, and bringing a programmable coordinate measurement machine into the counterbore and into successive contact with three spaced points about the counterbore by three programmed straight line motions in order to determine the coordinates of the centerline of the counterbore and thus the center bore of the threaded hole in the workpiece.

The method of determining the distance between the centerlines of two threaded holes formed at spaced points at a planar surface of a workpiece, using a programmable coordinate measurement machine, comprising:

• placing locating fixtures into each of the holes, the locating fixtures each having a cylindrical section threaded to mate with the threaded hole and each having a head section formed with a counterbore, the counterbore being concentric with the cylindrical section, bringing the probe of a programmable coordinate measurement machine into one of the counterbores and moving the probe into contact with three spaced points on the surface of the counterbore, moving the probe into the counterbore on the second fixture and contacting three spaced points on the interior diameter of the counterbore of the second fixture, and calculating the centerlines of the two spaced holes and the distance between the centerlines.