whenever the frictional contact alone between the live
center and the work is not sufficient to drive the work.
Figure 6-26.--Cutaway showing the construction of a hall
bearing center.
The common lathe dog shown at the left in figure
6-28 is used for round work or work that has a regular
be interchanged. A dead center requires a lubricant
section (square, hexagon, octagon). The piece to be
between it and the center hole to prevent seizing and
turned is held firmly in the hole (A) by the setscrew
burning of the center. (NOTE: There is a groove
(B). The bent tail (C) projects through a slot or hole
around the hardened tail center to distinguish it from
in the driving plate or faceplate so that when the
the live center.)
faceplate revolves with the spindle, it also turns the
work. The clamp dog illustrated at the right in figure
The centers fit snugly in the tapered holes of the
6-28 may be used for rectangular or irregularly
headstock and tailstock spindles. If chips, dirt, or
shaped work. Such work is clamped between the
burrs prevent a perfect fit in the spindles, the centers
jaws.
will not run true.
To remove the headstock center, insert a brass rod
CENTER REST
through the spindle hole and tap the center to jar it
loose; you can then pull it out with your hand. To
remove the tailstock center, run the spindle back as far
The center rest, also called the steady rest, is used
as it will go by, turning the handwheel to the left.
for the following purposes:
When the end of the tailstock screw bumps the back
of the center, it will force the center out of the tapered
the most commonly used center for working between
centers. As your work expands from the heat
generated from machining, you should occasionally
feel the area that houses the ball bearings to make sure
they are not overheating. If the bearings become too
warm, you will need to decrease the pressure of the
center against the work.
For machining hollow cylinders, such as pipe, use
shows its construction. The taper shank (A) fits into
the head and tail spindles in the same manner as the
lathe centers. The conical disk (B) revolves freely on
the collared end. Different size disks are supplied to
accommodate various ranges of pipe sizes.
LATHE DOGS
Lathe dogs are used with a driving plate or
faceplate to drive work being machined on centers
6-16