( 7) Threading o r chasing tools (119). There are many patented types of threading tools. The tool shown is provided with a formed cutter which i s sharpened by grinding the top face only. On some classes of material where it i s not possible to cut a smooth thread with a rigid chasing tool, a spring threading tool (120) will produce better results. The boring bar shown in illustration (122) is used for medium size holes and is adjustable for different depths of holes. It i s held in the regular tool post by a shank, the same a s the turning tool.
The spring threading tool i s built with a nut for the lockable spring head which provides a rigid backing for coarse threads and heavy cuts, and when loosened, the holder becomes a spring tool for finishing work. Neither of these tools is absolutely essential a s most threads can be cut by grinding a tool bit to the proper shape, with the use of a thread gauge. Figure (123) shows a boring bar for heavy work that is held in the compound rest T - slot. This makes the bar more rigid than when held in the tool post. Various shaped tool bits for boring, facing, counterboring and threading holes can be used in the different bars. (8) Boring bars and holders.
Tools of the type shown are used for boring holes and chasing internal threads. Two basic types of boring bars are used, namely, the forged type and the bar and holder type. Three of the bar and holder types are shown in the accompanying illustrations. No. 121 i s used for small holes, which in addition to holding bars with bits a s shown, can be used to hold boring tools made of drill rod for very small holes, and also for holding drills for drilling. (9) Knurling tool (124). On some classes of work such as thumb screws, hand - reamers, plug gages, etc., it is necessary to roughen the diameter to give a better grip and prevent oily fingers from slipping.
This is called knurling and is used extensively on optical, radio and other electrical work. A tool holder carrying two knurled wheels is fed into the work while it is revolving and impresses a pattern on the work. Extra wheels can be obtained for the knurling tool holder to cut various patterns. Nomenclature of Lathe Tools OFFICIAL A.S.M.E. DESIGNATIONS O F TOOL B I T ANGLES I ANGLE SIDE RAKE WORK SURFACE - FRONT CLEARANCE 3ff-' BACK RAKE GRINDING -(c&EWcK R A K E ANGLE ANLLE FINISHED SURFACE LSIDF CLEAR A NCE