Tips for turning Acme worm threads

摘要

Cutting Acme threads on the lathe seems to daunt even some experienced home workshop engineers. Broken down into simple steps, however, the process is quite manageable. In a previous article I outlined how to make two substitute worm wheels for my fabricated version of G. H. Thomas's classic Versatile Dividing Head, photo 1, These now require two slightly different forms of worm threads screwcutting to engage them without needing the worm set at an angle to the wheel. The first, larger gear used was a surplus Myford change gear, having straight cut teeth. The matching worm will have to be turned with a thinner than standard thread profile so it can be rotated the 4.5 degrees to the straight position and still engage the gear.