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The drilled hole has a polygonal shape. Why?
This may be due to runout during drilling.
(1) Runout when installing the drill.
Solution: Keep the installation slip within 20 μm (0.020 mm).
(2) If the lip height of the drill at regrinding time (variation in the height of the left and right cutting edges) is large, the drill tip will swing during machining.
Solution: Review regrinding
(3) The drill is swinging at the entrance of the hole.
Solution: Increase the feed per rotation and press the drill so that it does not swing. (Suppression by thrust resistance)
~Poor roundness~
