Lathes Page: 11
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way of making boring tool holders is to broach a hole in a bar or
rod of proper size to hold the tool bit. A set screw or other suitable
device is used for holding the tool bit firmly in place.
d. Form threading tools (fig. 7) have the thread form and proper
relief ground on them by the manufacturer and therefore remain
true to form and of correct angle, if the sharpening is done on the
Fli : 7. Fo in tlini:ulin tool.
top edge only. This type of form threading tool insures better
fitting threads and saves much grinding time.
e. The knurling tool holder (fig. 8) has a revolving head contain-
ing three pairs of knurls. It is used for rolling depressions into the
surface of work both for decorative purposes and to furnish a better
grip on the handles of various tools. Figure 48 shows the three
FIGURE 8.-Knurling tool holder.
grades of knurl rolls and illustrates the pattern that each set makes.
8. Cutting speeds and feeds.-a. In order to machine metals
successfully, careful attention must be given to the speed at which,
the work revolves and the distance the tool advances during each
revolution. These are known as "cutting speeds and feeds." Cut-
tin speed, which is usually given in feet per minute, is equal I)
' " >d, f
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United States. Army. Air Corps. Lathes, book, November 29, 1940; Washington, D.C.. (digital.library.unt.edu/ark:/67531/metadc96655/m1/13/: accessed September 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.