Tools are sometime specially ground, how ever, for parting very soft metals or specially shaped .
The end is sometime ground on a slight angle when a series of small hollow pieces is being ough many cutoff(…………..)
Tools that have been ground back for resharpening too many time often from a “ chip trap”
Causing the metal to be torn off or the tool not to cut at all(…….)
Although many modern lathes have toolholders that hold the built-in back rake so it is not necessary to grind one into the tool as in(……….)
Threading tools(……….) should always be checked with a center gage for the 60-degree angle while thay are being ground or sharpened. Various kinds of threading tools can be made to suit the application.tool for brass or plastics should have zero to negative rake,back rake, and relief angles are given for tools in table I-2