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1 以高速鋼鑽頭在鑄鐵上鑽削30mm孔徑,若切削速度為25m/min,則鑽床主軸轉速約為
A 145rpm
B 185rpm
C 225rpm
D 265rpm

N = 1000VπD

= 1000×25π×30

=265(rpm)