Gonna try to sort this out again. I went to the metalworking discussion looking for the same answers and got rather curt and unsatisfactory responses. Guess they kinda get their panties in a bunch when a sawduster enters their domain.
I "inherited" this three-jaw chuck when I purchased a used lathe, and it seems to me that it's a metalworking unit. There's no trademark on it. The darn thing is quite heavy (15-20 pounds) and the body is closed with a diameter of six inches. The jaws are straight (no dovetail) and grooved, stepped, and reversible. The metal guys said is wasn't any good for their work and was probably a low-end woodworking unit, but I've never seen anything like it in the woodworking community.
Three-Jaw Chuck.jpg
Here's my take: Because it's heavy, it's useful for rough-turning irregular blanks as long as it's used with the tailstock engaged. The size and bulk acts like a flywheel and tends to balance the object. And the three-jaws means it can grab onto just about any shape (four jaws can't) and the range of opening (1" to 7") makes it useful. I sometimes wrap it in cloth and use it to nervously hold the ID of a nearly-finished bowl to trim the bottom when the softjaws won't fit. BUT-- the lack of tapered jaw faces doesn't hold pieces as well so I don't trust it for my finished work and almost never use it without securing the tailstock.
Three-jaw chucks for metalworking are surprisingly expensive -- $300-plus is not uncommon -- despite what the metalworking guys said.
Not sure if I should keep it or sell it. I've thought about modifying the jaws but that's really hardened stock. Have any of you old-timers seen/used one of these before? Your thoughts?