Wednesday, June 10, 2009

Full circle

One of the machinist forums I read had a posting from someone who made a Geneva drive. The disk at the top rotates and the pin, which you can just see at the top left side, catches in the one of the grooves of the elegant piece at the bottom. As it catches the groove it turns the bottom piece, which then pauses until the next groove is caught. There are some animated illustrations of how it works on Wikipedia.

After reading comments of admiration on the machining skills one person asked what use anyone would have for such a thing. I wondered myself and checking Wikipedia discovered the purpose is to change a continuous rotary motion into an intermittent rotary motion. It was first used in clock and watch making where you need to convert a continuously wound spring into intermittent ticks.

Kind of interesting but what caught my attention is that this drive is also used in CNC machines (aka computer driven mills and lathes). Aha! I had a morsel of machining knowledge that my more experienced confreres perhaps did not know. I zipped back to the forum to post and discovered someone already posted they had been using one on a lathe. "I had no idea that's what that was called. Turret on big Warner Swasey VTL uses that for indexing the tools."

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