Although top rake has been shown for the purpose of illustration, it is not essential, and is often omitted, in order that the height of the cutting edge may remain nearly constant as the tool is resharpened.

The clearance and rake angles indicated are suitable for a tool used to turn mild-steel to a good finish, either when being traversed along the work or when facing a surface. Although in a tool of this pattern the whole width of the front face might be presented to the work, this would probably cause chatter and an inaccurate finish, due to the great pressure exerted on the work by the large area of contact.

It is usual, therefore, to form the tip of the tool as shown in Fig. 19c, so that the width of the cutting edge is much reduced by imparting what is termed relief behind the n

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