TRUING A THREE OR FOUR JAW

SELF CENTERING CHUCK

 

The jaws that are more suitable for use with non ferrous, soft materials like brass, aluminum, plastics, and wood, are called soft jaws and are made of aluminum, as hardened steel jaws, unless padding is used to protect the work will dig and mar the work surface especially when a piece is reversed and gripped around a newly machined surface. The soft jaws as usually furnished are in an un-machined state but is not as bad as it sounds. If you try to use them to hold material as they are, you will find that the inner bearing surfaces may hold the work slightly off center and have a pronounced runout. The inner griping surfaces of the chuck jaws need to be lightly machined in a boring type process to bring them all to not only a concentric condition but also perpendicular to the chuck and parallel to the lathe axis. Open the chuck about mid way and insert a very thin steel washer about an inch in diameter into the opening between the jaws and while pushing it firmly against the back of the chuck face, tighten the jaws. This will tension the jaws outward the same way as they would be when they are gripping a piece of stock. With a boring bar and a medium to slow speed of the spindle, you should begin to take light cuts along the inside surfaces of the check jaws. Check each jaw after every pass to see how the work is progressing and quit as soon as three jaw's griping surfaces are evenly machined along their whole length. Doing it this way will insure that the jaws will hold a workpiece as concentric as possible for the type of chuck it is.

The inner surface of the newly machined jaws can be left smooth or it could have a couple of little grooves cut into them for better gripping power. The runout can measured by gripping a short piece round 1/2"drill rod and taking a dial indicator reading from the surface of the rod while watching the indicator needle for any fluctuations as you hand turn the chuck. It should be well within .001" to .0005" although depending of the quality of the scrolling mechanism, it may be less. Because the jaws are relatively soft, they will not withstand excessive abuse and may have to have its griping surfaces lightly machined every once in a while as a matter of maintenance to keep them in tune. The blank set of jaws for the TAIG chucks are very low cost and several sets can be machined for special purpose jobs without much in they way of expense.