Thread-cutting methods; a treatise on the operation and use of various tools and machines for forming screw threads, including the application of ... machines, and thread-rolling machines

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. 1918 Excerpt: ... the hole may be the fault of the tap or it may be caused by the method of holding it; the size of the hole before tapping is also frequently the cause of inaccurate work. If the threaded part of a solid tap is warped or bent slightly by the hardening operation, this will cause it to cut large, the error increasing as the length or depth of the tapped hole increases, up to the full length of the tap body. When taps are made of steel that is not properly rolled or annealed they may shrink unevenly in hardening or lose their circular form. If the teeth of an evenly fluted tap do not lie in a circular path, the tap will chatter and cut over size. A tapped hole that is too large may also be caused by the crowding of the metal resulting from passing a tap through a hole that is too small. Errors may also be due to excessive clearance or rake on the chamfered part of the tap, uneven chamfering on the different lands, excessive under-cutting in the tap flutes, or too much relief in the thread angle. Lack of alignment between the tap and work is frequently the cause of tapping holes that are too large and tapering. The extent to which errors from lack of alignment may be reduced, if they are not eliminated entirely, by the use of floating tap-holders depends upon the design of the tap-holder and the amount of alignment error. By studying the different causes of error mentioned, tapping troubles that are the direct result of one or a combination of these causes may be greatly reduced or eliminated, and holes may be tapped accurately enough for ordinary commercial requirements without purchasing taps made to order and within specified limits of accuracy which require unusual and unnecessary refinement in their manufacture. Speeds for Tapping.--The speeds for tapping ...