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.
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.
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.
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.