Smithy Midas 1220 LTD - Manual (Page 51)

Figure 10.16 Four-jaw independent lathe chucks hold round, square,
eccentric, or odd shaped workpieces. and Figure 10.17 Three-jaw universal geared scroll
chucks hold round or near-round workpices.
Mounting Work in a Four-jaw Independent Lathe Chuck
For small-diameter, short work, insert jaws in the chuck with high ends to the center. This
gives the maximum gripping and tool clearance (Figure 10.18). For large-diameter work,
insert the jaws in the chuck slots with the high steps of the jaws to the outside of the
chuck (Figure 10.19).
To place work in a chuck, follow these steps:
1. Adjust the chuck jaws to the approximate opening to receive the work. Roughly
center them by matching the nearest concentric ring on the chuck face with the
corresponding mark on the jaws.
2. Place the work in the chuck and grip it. Turn up the opposing jaws a uniform number
of turns with the key provided. This will hold the work in position. Then bring in the other
pair of opposing jaws the same way.
3. Revolve the spindle slowly with your left hand while holding a piece of chalk until the
chalk touches the high point (the nearest surface) of the work (Figure 10.6).
4. Guided by the chalk marks, readjust the jaws until a chalk line lathe chucks hold round,
will carry completely around the work. Then tighten all the jaws securely. square,
eccentric, or odd-shaped workpieces.
For greater accuracy, after roughly centering the stock using chalk, set a dial indicator at
the back of, and square to, the stock. Make sure you can see it clearly. Rotate the chuck
by hand. Looking at two opposing jaws, determine which side is higher. Align the higher
side with the dial indicator, loosen the opposite jaw, and tighten the higher jaw. Do the
same with the other two jaws. Repeat the process until you have located the stock
within necessary tolerances.
When making several identical pieces, after completing each workpiece release only two
adjoining jaws, leaving the others to hold the center. The jaws of the four-jaw
independent chuck are reversible. You can insert them with high steps to the inside or
outside.
10: Setting Up with Centers, Collets, and Chucks
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