Shafting is usually turned 1/16 inch less than the nominal diameter. For instance, instead of a shaft 2 inches in diameter, one of 1 15/16 inches in diameter is used. The reason is that iron of a nominal diameter of 2 inches, usually 1/32 inch over size, can be used. Before turning a length of shafting, the rough bar should be carefully straightened. After the center holes have been drilled and the piece placed in the lathe, the work can be rotated, and the eccentric portions marked with chalk. When this has been done, the bar should be removed from the lathe and sprung back into true alignment. It is well to take two cuts in finishing shafting, one for the roughing cut, and one very fine finishing cut. The tool for the latter part of the work should be kept flooded with oil or with a solution of sal soda. If the work is light, a tool holder, carrying both the roughing and the finishing tools, may be used. This makes it possible to do the work in practically the same time as for one cut.

Preventing Spring in Shafting

As a length of shafting is likely to spring under the pressure of the tool, some method of preventing such action must be employed. A center rest can be used. It is, however, inconvenient, and must be frequently moved, or at times it will stand too far from the tools. Furthermore, as the rough bar will neither be truly round nor concentric with the centers, it is necessary to turn spots for the center rest. Spotting, however, takes considerable time, owing to the fact that very light cuts must be taken in order to avoid springing the bar. A good method is to have a ring attached to the tool holder; the internal diameter of this ring is that of the finished shaft. It is slipped over the tail-stock center, and follows the finishing tool. It must, of course, be rigidly fastened to the tool holder. In this way the shaft is supported close to the tools; the ring also serves as a gage to measure the diameter of the shaft. If, for any reason, the tools turn to a larger diameter than the inside of the ring, notice is immediately served upon the workmen to that effect, by binding in the ring.