Elementary Machine Shop Practice (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 Excerpt: ...mechanism that controls the feed, or travel, of the tool when cutting threads is independent of that used for the feed when doing plain turning. The two feeds usually run at different speeds so that if they are both in action at the same time the gears in the carriage will break. For this reason all lathes are provided with some means of disconnecting the feed used for plain turning when cutting threads. To disconnect the feed on the lathe shown in Fig. 73, move the lever J to the central, or neutral, position. This should always be done before starting to cut the threads. Speed of Lathe.--The lathe should run slower for cutting threads than for plain turning. With most lathes if the belt is on the largest step of the cone it will give about the right speed for cutting the threads in this problem. The object of running the lathe slowly is to give the operator time to draw back the tool at the end of the cut and to obtain a smoother cut. If the speed of the lathe is too fast, the cutting action will be so quick that the tool, instead of cutting clean and smooth will tear out the metal, leaving a rough surface. The slower the lathe runs the easier it is to cut the threads, but it will also take longer to do the job. It therefore requires practical experience to determine the proper speed to be used for cutting the different size threads. Chamfering.--After the lathe and tool are properly set, chamfer off the sharp corners where the threads begin and end with the side of the thread tool. The depth of this cut should be about the same as that of the threads when finished. If the corners are not chamfered, the threads, when cut, will form a very thin edge, or fin, at the ends. Use of Adjustable Stop.--To regulate the depth of each cut CHAMFERING 63 an adjustable...