CNC Turned Parts-Using the Soft Jaws
Soft jaws are very useful when a component has to run dead true in the jaws, for example when making something like a grinding spindle where concentricity is important.
Soft jaws likely to be found in the home workshop are simple rectangles of steel with the scroll and groove formed directly into the soft jaws. Another type of jaw you may come across has a grooved pattern in the main jaws that matches a similar pattern in the actual soft jaws. The soft tops of these jaws are usually inter- changeable. They are more likely to be found on larger chucks, but you could make your own version for the smaller sizes of chuck if you wish.
The main use of soft jaws is for second operation work, for example when you have turned a component complete from a bit of bar and parted it off. Now you need to hold the component true to finish off the second end. You can do this by boring out the chuck jaws to the exact diameter of the workpiece. To bore the soft jaws, they should be tightened in the same direction as they will be tightened in use, so that they are operating on the same part of the chuck scroll every time. If you have a thin component to machine, fit the soft jaws to the chuck and tighten the jaws onto a bit of bar held in the chuck. Be sure to leave enough space in front of the bar so you can bore the jaws to fit the work.
