MMMmmm. Are we talking about the same type..They are usually fitted on CNC lathes. The lathe will have a rotary cylinder at the end of the spindle and a draw tube will run through the spindle connecting the cylinder to the chuck. You activate the cylinder and it pulls the collet into to body and thus grips the material.
It seems at the end he turns the key but i don't think my key does anything. It turns about 5 turns and goes solid but his seems to click and rotate again mine doesn't.Ah probably not seeing as how that is a manually operated one
I thought that might be the case but the front of the chuck alters the grip on the part. I thought the key might lock the front in place but o can still turn it...lol when i get it mounted to the backplate i will have another look.I don't think the clicking/rotating of the key is anything other than a safety feature so that you can't crank the pressure up too much, sort of torque wrench style, when it gets to a certain torque the key wont tighten the screw any more as it just clicks round.