Nothing much happens in this video but you get to see how to set up a Mini-Lathe to turn plastic rod (Teflon) to a precise diameter. In this case, the rod started out as 3/4″ nominal, and I turned it to .736 ± .0005″ over its 3 ft length. The idea is that the rod is fed through an ER-32 collet (3/4″) at a precise rate. I made an add-on assembly that supplies feed pressure. A rotating threaded rod propels a foot that pushes against a feedrod which pushes the workpiece. Rotation is supplied by a 12V windshield wiper gearmotor with a pulley epoxied to it. The trick is to get the collet tight enough to grip the workpiece so the mini-lathe can rotate it for turning, but not so tight that the workpiece can’t slip through it as the feedrod pushes against it. The more consistent you can get the collet tightening every time, the more precise the turn will be rod after rod. Once you get the diameter set, you lock down the cross slide gibs and lock down the carriage and just do rod after rod. For the turning tool, don’t use anything made for metal, the angles are all wrong. You want plenty of rake on all sides of the tool, especially the front, where you want plenty of “bite”. And sharpen the tool knife sharp so the swarf comes off like peeling a potato. The top rake determines which way the swarf goes. If you set it up right, the swarf comes off in a string which drops itself to the floor. The workpiece is supported by a 3 bearing type steady rest. The video finishes up with a short clip that shows one of the travel limit switches that stop the motor just before the end of the workpiece pops out of the collet. The black switch allows me to reverse the motor to draw the foot back so I can start over. Thanks to Bobby Hill Machining of Redway, CA for the idea.
Post time: Jun-30-2017