Machining the 'Quorn' Spiral Column on a Vertical Miller

摘要

The 'Quorn' Universal Tool and Cutter Grinder (ref. 1), designed by the late Prof. D H Chaddock, is popular among model engineers. Its construction is not without challenges and one of the most awkward machining tasks is the wide pitch (half to three-quarter inch) spiral groove specified for the column which carries the grinding spindle and motor assembly. Although not essential for proper operation of the machine the spiral groove allows for easy fine adjustment of spindle height and also serves as a safety feature which prevents the spindle/motor assembly from dropping precipitously down the column if it is inadvertently unclamped. The spiral is clearly not difficult to machine given the appropriate equipment. The problem is that most small lathes are not designed to provide the wide pitch required. Professor Chaddock suggested one way in which the machining could be carried out on a Myford ML7 lathe but his method is not applicable to some other lathes. One expedient, which the author remembers was suggested in a letter to a model engineering magazine, is to take the column to a professional machining centre and have the groove cut using CNC equipment. The dyed in the wool model engineer (include yours truly) would probably hate having to do this; so what are the alternatives? There must have been a number of different approaches to the problem but few appear to have been published. The author's solution was to carry out the machining on a vertical mill.