Number of drill blows per minute. hope this helps !!
Explanation:
There are two rake angle types :
Positive rake
This is the case that occurs when looking from the inner side the face of the cutting tool slopes away from the cutting edge.
Negative rake
This is the case that occurs when the face of the cutting tool slopes away from the cutting edge at the outer side.
Increasing the positive rake angle means that the cutting tool will get sharper thus making the tool weaker. So, brittle material will form discontinuous chips and ductile material will form continuous chip. The tool life may also be reduced.
Increasing the negative rake angle means that the cutting tool will get blunt thus making the tool stronger. So, brittle material will form continuous chips. Results in higher temperature of the tool. Surface finish might increase.
