CTC Machine in Theory & PracticeAGP Laycock

摘要

The original segments of eight inch diameter were milled with 50 spiral grooves, spaced evenly around the circumference, by a standard angular milling cutter. Just why McKercher should have chosen this number cannot be known for certain, but it is interesting to note that a circle of eight inches diameter, when it is divided by fifty, provides divisions on the circumference of near exactly a half inch ! Parallel grooves crossing the spirals, were formed by a tool normally used for shaping the threadof a bolt, along the length of the roller, thereby creating the "teeth" of the segments. To do this, UMcKercher chose one of many such 'chasing tools' as being the most suitable for his purpose, which had a pitch of eight teeth per inch of the British Standered Whitworth (B.S.W.) pattern. Again, it is of interest to note that by employing a milling cutter of 70U angle in milling the spiral grooves, McKarcher formed the teeth of his rollers on this eight inch diameter, having the two longitudinal characteristics of the "shoulder" and "backslope" in approximately equal proportion. Why use a Helical Pattern? Because if milling is performed in a straight line at 90 U to chased grooves, all the teeth in a row wd cut togather at same time in a shock wave and happening 50 times per min, resulting huge vibration and power consumption, whereas with helical grooves it wd be each tooth following behind another and as the roller revolves, cutting is progressive down the row with no shock wave.