The router lathe spins the screw blank between centers while a router slowly traverses from right to left, truing the blank. I made this around 1996 for a PBI class at Penland. It wasn’t motorized then so the students had to crank it by hand.
The blank is driven at the headstock by a nail that engages a plastic rod. At top right is a microswitch that shuts the machine off when a blank has been completed.
At the tailstock end the blank is held by another center. This one is pushed by a weighted lever, holding the blank securely between centers at both ends while it is shaped.
A view of the weighted lever that pushes the pointed center into the blank. The pressure can be released by using the plywood prop so that a finished blank can easily be removed and a new one inserted.
The tailstock center is made from a piece of 1/4″ drill rod with a 60 degree point. The hex bolt that can be seen is one of four. They enable very fine adjustments to insure the blank is turned to a true cylinder without taper. The diameter that is machined on the screw blank can be easily held to within a few thousandths of an inch.
A blank has just been finished. The white plastic part on the left is the thread follower. It engages the two small lead screws and controls the router’s forward motion. The router is tipped up to show the bit and how it is guided along the rails. The router is pulled along by a cord which is weighted at its other end. The bolt head visible at the left is a stop that can be adjusted to correctly trim the edge of what will become the screw handle.
The thread follower can be easily snapped on and off so the tool can be quickly re-set to make more screw blanks.
First the far side is snapped in place and then the front is snapped down on the other lead screw.
The thread follower is just visible beneath the front edge of the router base.