I've got a simple newbie question about workholding on the lathe. If I wanted to turn some chess pieces 1.5-2.5" long, they'll be supported by the chuck only - no tailstock, how much metal do I need to have sticking in the jaws/collet of the chuck? Is there a rule of thumb that says X% of the piece should be held or is it just whatever amount it takes to get a solid grip?
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How Much in the Chuck?
- Thread starter joe_m
- Start date
A hard question to answer. It depends upon many things. What kind of metal? Aluminum or brass is more easily displaced than steel,and marred or dug into by the chuck jaws. The design of the pieces,etc.. The best thing to do is take a longer bar,and make a chess piece,cut it off,and advance the bar for the next one. That is the most economical way of doing it,from a standpoint of left over metal stubs. You will only have 1 left when you use up all of the bar.
George makes good points, but if you don't have enogh spindle bore for using one rod....
I personally never put less in the chuck than to the 1st step unless making only very light cuts. Think of needle nosed pliers and to much force springing them if the work is held to close to the tips. With less in the chuck more chance of slipping, more tightening and more stress on the tips of the chuck jaws. If the material slips and the tool digs in there could be enough stress to spring the jaws and upset the acuracy and parralel of the jaws.
Steve
I personally never put less in the chuck than to the 1st step unless making only very light cuts. Think of needle nosed pliers and to much force springing them if the work is held to close to the tips. With less in the chuck more chance of slipping, more tightening and more stress on the tips of the chuck jaws. If the material slips and the tool digs in there could be enough stress to spring the jaws and upset the acuracy and parralel of the jaws.
Steve
In general, it's best to have enough stock in the jaws to contact the entire length of the jaw. In an extreme example, if you only chucked 1/8" at the very tip of the jaws, the chucking forces will act to spring the front face of the chuck and make the jaws out of parallel. Remember where the force comes from. The screws of a 4 jaw, or the scroll of a three jaw are set back a ways behind the face, and they act on the back surface of the master jaws in the case of 2 piece jaws, or simply the mating threads of a 4 jaw screw or a 3 jaw scroll. As this pressure mounts towards centerline, with nothing back far enough in the chuck to constrain it, the force concentrates nearer the end of the jaws, with considerable leverage. That's the risk there. Of course, lightly controlled chucking pressure poses little real danger of damage, but caution is advised. It is best to allow full length jaw engagement onto the bar.