JMB Milling Machines
Made by the same German company responsible for a range of small but heavily-built millers, the JMB precision drill was also a rugged affair. A tightly-constructed machine, it had a round table machined with four radial T-slots, an integral motor, variable-speed drive and a built-in light. Giving a range from 1500 to 5000 r.p.m. the variable-speed drive system was a friction type, the 250 Watt, 2800 r.p.m. 50 Hz motor able to be slid backwards and forwards by moving a lever on the left-hand face of the main body. On the motor spindle was a rubber tyre, this pressing against the face of a steel disc attached to the main spindle. As the motor was moved forwards towards the centre of the disc the speed was reduced, while moving it backwards caused it to increase. A simple system and one perfectly suitable for drilling small holes up to 0.25" (6 mm) in diameter. A number of machine tools have been built with a similar friction drive including the Bulgarian Mashstroy lathe, American Elmco, Schaffner and Onan lathes, the German Robling and Boley F1 high-precision watchmaker's lathes - and some examples of German Klopp and American Hendey shapers. A reversing cone-type friction drive was also used on the English Oldak and Apex tapping machine, but this was not a variable-speed type.
If you have a JMB machine tool, the writer would be interested to hear from you