Fig. 4.31. Comparison of Roughing Cuts28
Blunt point angles (140°) work best for small diameter holes (1/4in. and less), while sharp points (90°) work better for larger diameter holes where higher pressures are needed to feed the drill. Relief angles also affect tool life; too small a relief angle will cause smearing and galling, while too large a relief angle results in edge chipping. When drilling holes deeper than one hole diameter, peck drilling will produce more consistent and higher quality holes. During peck drilling, the drill motor periodically extracts the bit from the hole to clear chips
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