WORK HOLDING DEVICES OF CAPSTAN LATHE
The
work holding devices used on the capstan lathe are generally automatic
type. These automatic type work holding devices reduces the setup time.
1. COLLETS
Collets
are also called as collet chucks. It is mainly used to long bar stocks
of various shapes operated either by hand or by power.
Collets
generally have 3 or 4 slits with a taper nose with a bore at its center
to receive the work piece. The tapered nose is made thicker for holding
the work piece. The bore may be of different shapes like square,
circular, hexagonal, etc., depending on the work piece.
COLLET
VARIOUS TYPES OF COLLETS
(a) DRAW BACK COLLETS
It
is also called as draw in collets. The taper of the collet is smoothly
converging inwards. The collet is fitted inside the taper portion of the
spindle nose. Collet is moved behind or forward with the help of a
thrust tube. This action of collet holds the bar stock by applying
pressure on the collet and pushes axially in wards. So enabling the
collet to clamp the work piece by pushing inwards.
(b) PUSH OUT COLLET
The
taper of the collet converges towards the right end. In order to hold
the bar stock the collet is pushed into the tapered hole by the thrust
tube which closes the jaws and grips the work piece. To release the work
piece from the collet the collet is drawn in.
(c) DEAD LENGTH COLLET
In
draw back collets and push out collet while gripping the bar stock it
may move inward or outward. In order to rectify this a sliding sleeve is
provided in between the spindle and the collet. When the work piece is
clamped the sleeve pushes through thrust tube by applying force on the
collet. Which implies that there is no axial movement either inward or
outward.
2. POWER CHUCKS
Power
chucks are mainly used for holding heavy work piece with more gripping
force. These are operated either pneumatically or hydraulically. The
fluid cylinder is fitted at the back of the head stock. A piston rod is
used for connecting the piston with the jaws with the help of links
which is actuated by sliding piston.
3. FIXTURE
Fixture
is a specially designed component to locate and grip the work piece.
Chucks and collets are replaced by the fixture and mounted on the
spindle. Fixture are generally use for machining a large no of similar
pieces. When fixture is mounted on lathes it is called as turning
fixtures.
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