Mr. Eisenberg. But the markings, you said, would be different on two consecutive bolt faces?
Mr. Frazier. Oh, yes.
Mr. Eisenberg. And if the tool is not changed, what is the origin of the difference between the markings?
Mr. Frazier. There are other accidental markings placed there during the machining operation.
Mr. Eisenberg. Could you describe that?
Mr. Frazier. For instance, as the blade of a milling machine travels around a surface, it takes off actually a dust—it is not actually a piece of metal—it scrapes a little steel off in the form of a dust—or a very fine powder or chip—that tooth leaves a certain pattern of marks—that edge. That milling cutter may have a dozen of these edges on its surface, and each one takes a little more. Gradually you wear the metal down, you tear it out actually until you are at the proper depth. Those little pieces of metal, as they are traveling around, can also scratch the face of the bolt—unless they are washed away. So that you may have accidental marks from that source, just in the machining operation.
Now, there are two types of marks produced in a cutting operation. One, from the nicks along the cutting edge of the tool, which are produced by a circular operating tool—which produce very fine scratches in a circular pattern. Each time the tool goes around, it erases those marks that were there before. And when the tool is finally lifted out, you have a series of marks which go around the surface which has been machined, and you will find that that pattern of marks, as this tool goes around, will change. In one area, it will be one set of marks—and as you visually examine the surface of the metal, these very fine marks will extend for a short distance, then disappear, and a new mark of a new type will begin and extend for a short distance. The entire surface, then, will have a—be composed of a series of circles, but the individual marks seen in the microscope will not be circular, will not form complete circles around the face of the bolt.
Mr. Eisenberg. Have you had occasion to examine two consecutive bolt faces from a factory?
Mr. Frazier. Oh, yes.
Mr. Eisenberg. And what did you find on that examination?