The Pratt and Whitney Company, who are the manufacturers of this holder, make this angle of clearance 15 degrees. The height of the tool in the holder is adjusted by the screw s, which has journal bearing in the holder, and threads to the end edge of the tool.
Now it is obvious that the holder h, once being set to its proper position in the tool post, the tool t may be removed from and replaced in the exact same position, both in the holder and with reference to the work.
Fig. 1025.
In [Fig. 1025], for example, is a top view of the holder with a single-pointed threading tool t in place. w represents a piece of work supposed to be in the lathe, and g a tool-setting gauge; and it is obvious that, if the holder is not moved, the tool t may be removed, ground up, and replaced with the assurance that it will stand in the exact same position as before, producing the exact same effect upon the work, providing that the height is maintained equal, and the tool is not altered in shape by the grinding. To maintain the height equal, all that is necessary is to have the upper face (h, [Fig. 1024]) of the holder horizontally level and in line with the line of centres of the lathe, and to set the top face of the tool level with that of the holder. In sharpening the tool the top face only is ground; hence the angles are not altered.
Fig. 1026.