This is a lever operated collet closer I made for my 7x10 mini lathe. I copied from pictures of different models but made it smaller and for 3C collets. It can open and close with the lathe running and works great with my bar feeder.
Like many older designs it pulls the collet into the spindle to tighten it, with the lever mechanism at the far end of the headstock. The collet seats in a MT3-to-3C spindle adapter from Little Machine Shop, and the drawtube screws onto the collet and passes through the spindle, supported by a bushed adapter screwed onto the rear spindle threads, replacing the bearing jam nut.
The lever shifts a cam to spread three lever fingers that press against the end of the spindle and pull the collet into the spindle nose. I think like old Royals, and the Rovi shown below, the cone-shaped working surface is on the outside of the cam, and it has flats at both ends of the cone to limit the motion of the fingers and prevent it from releasing itself. Clamping force is pre-set by screwing the drawtube into the the collet and then locking it with a dog point set screw in one of the slots in the rear spindle adapter.
It has been reliable so far - I havenít made very many parts with it but hopefully it will be durable enough for my purposes. The drawtube is a piece of 1/8Ē wall 1/2Ē mild steel DOM tube but many of the rest of the parts are harder steel and bronze.
main view with guards removed; closed and open
shell guard tapped for the indexing screw and the slots that goes in; rear spindle adapter with closer removed
most of the parts before it was completed; some unused and undrilled fingers
Here is a very short video showing the collet in use, with it opening to let work feed up to a stop.