Use of Micrometer for Internal Thread Cutting
Fig. 33. Method of using Micrometer for Internal Thread Cutting
Fig. 33 illustrates a means of determining the size of internally threaded work. The work shown is intended for a lathe chuck. The outside diameter of the hub on the work is turned to the same size as the hubs on small faceplates which are furnished with all new lathes. The threaded size is then taken and transferred with a micrometer, over the anvil of which is fitted a 60-degree point as shown enlarged at A. In connection with a graduated cross-feed screw this greatly facilitates the work over the usual cut-and-try method.[[18]]
Inside Micrometer
The inside micrometer shown in sections in Figs. 34 and 35 is adapted to measuring, by use of extension rods, from 2 inches up to any size of hole, and has one inch adjustment of the measuring screw.
Figs. 34 and 35. Section of Inside Micrometer
Referring to the section shown in Fig. 35, the measuring screw S is secured to the thimble B with the screw D, the head of which is hardened and forms the anvil. By loosening this screw D, the thimble can be rotated to compensate for wear. The wear of the measuring screw and nut is taken up by screwing the bushing A into the frame with the wrench shown in Fig. 37. This bushing is split in three sections for about two-thirds of its length on the threaded end. The three small lugs on the wrench fit into these slots. The handle end of the wrench is a screw driver which is used for manipulating the set screw C. The bushing is made an easy fit in the frame on its plain end and tapered, as shown, on its outside threaded part. This thread being the same pitch as the measuring screw, adjustment for wear does not affect the reading of the micrometer. This manner of adjustment brings the nut squarely down on the measuring screw for its whole length, presenting the same amount of wearing surface after adjustment as when new.
