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Cutting a Helix with a Vertical Mill


I needed to cut a 1 thread per inch helix 0.1" deep into round stock. I did not want to spend months designing and building a fancy mill atachment. The design below is cheep, VERY dirty, but works well. All parts were in my junk box.

Basic Idea

The round stock is linked to the table feed with a 10 to 1 (thanks Tom) speed reduction. So as the table feed wheel turns ten revoltuions,  the round stock turns one revolution. One rev of the hand wheel advances the table 0.100" so ten revs of the hand wheel advances the table 1" plus turns the round stock 1 rev. Now, here is is "dirty" part: I wrap steel picture frame wire around both pulleys and tension it with weights. This provides the gripping so the wheels do not slip. The wire survives twice needed revolutions and then fails. So each time I cut a helix into a fresh piece of round stock, I replace the wire. I make the 0.1" deep cut in one pass.

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last updated 01/15/2004