When to switch jaws on lathe chuck

[Surprman]

Hi all,
I have two sets of jaws on my three jaw chuck for my lathe. Are there any rules regarding when you should to switch from one to the other? (other than when a diameter of the part won't fit). I have a piece that will fit in both, but there is about a half inch of the chuck jaw protruding outside the diameter of the chuck with the presently installed set of jaws. That seems less safe than using the set of jaws that are completely within the body of the chuck. I intend to use the presumed safer scenario, but I was just wondering if there is something more concrete to go by. (Or if I am missing something else I should consider)
thanks,
Rick

 

[JimDawson]

The rule of thumb that I use is that I try to keep a minimum of 2/3 of the jaw engaged in the scroll. Sometimes I go a bit less, but I'm pretty careful with the machining loads. I don't worry about the jaws sticking out a bit, but I make sure to keep my hands out of that area.

 

[12bolts]

pretty much what Jim said, but if the opposite set of jaws would not protrude from the chuck body then that would definately be the better/safer option.

Cheers Phil