In cutting larger sizes of pipes sometimes a special cutting-tool is introduced in place of the circular cutter to accomplish the more difficult work; in shop practice it is customary to cut the large sizes of pipe in a lathe or screwing machine.
Fig. 612.
Fig. 613.
Fig. 614.
The three tools shown on this page are designed to prepare the pipe for the reception of the threaded end of the pipe to be joined. The upper one, Fig. [612], is a reamer used to enlarge a hole, or to round up one that has been drilled or cut with a chisel, to prepare it for tapping. The lower, Fig. [614], is the tap which cuts the thread. The middle, Fig. [613], is a combined drill and tap which is operated by a ratchet and is used to drill and tap a hole in water pipe, etc., at one operation.
“Tapping” is the process by which the thread is formed in the interior of a hole, and is done with a tap; screwing is the reverse process by which the thread is formed on the outside of a cylindrical surface, as a pipe or round bar of iron.