Slow-helix drills

Drills with a helbc angle of 20 - known as slow-helix drills - are available with a point angle of 118 for cutting brass and bronze, Fig. 7.13(b), and with a point angle of 90 for cutting plastics materials,... 

Standard high-speed drills are satisfactory for use with plastics but must be cleared frequently to remove swarf. Slow-helix drills (20 helix) reduce the effect of swarf clogging in the flutes and, with a drill point of around 90 , give a better finish on breakthrough with the softer plastics. All drills should have an increased point clearance of 15 fo 20 . 

Figure 7.13. (a) Standard, (b) slow, and (c) quick helix drills... 

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