Further to Peter Rawlinson's article "Trepanning In The Lathe", issue 94, Nov 2003, I thought I would add my own experiences. Last year, I was given two pieces of flat mild steel. 1in. thick by 6in square. Both pieces came from the Royal Gunpowder Mills museum at Waltham Abbey in Essex, where I work as a volunteer. They are a grade of armoured steel plate used for ballistic testing. Although fairly tough, they are machineable. In fact, if you can get the machine speed down low enough, they mill, drill and turn easily. I asked for the plates for a specific job I had in mind. I wanted to make a small indexing table for my mill. After mounting the first plate in the four-jaw chuck of my Warco WMT 300, I hit the first major problem. With a minimum speed of 160 rpm, turning off the corners of the square material to create a 5(3/4)in. round disc was going to take forever.
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