Work Holding Devices of Capstan Lathe | Types of Chucks

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.


01 - collet chucks - job holder

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.

01 - draw back collet - types of collet

(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.

01- power chuck - work holding device

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.

Capstan Lathe Working Principle | Lathe Turret Head

CAPSTAN LATHE

Capstan lathe is one of the types of semi-automatic lathe. In semi-automatic lathes machining operations are done automatically. Functions other than machining like loading and unloading of job, positioning of tools coolant operations are done manually.

01 - capstan lathe - automatic lathe - engine lathe

1.BED

The base part of the lathe is the bed. It is made of cast iron. Guide ways are provided on the top of the bed. Cross slide and turret head are mounted on the guide ways. The bed should be strong and rigid to withstand loads force and vibrations during machining process.

2.HEAD STOCK

The headstock assembly is permanently fastened to the left end of the bed. Headstock of capstan lathe is similar to that of ordinary lathe. But it is heavier in construction . a powerful motor of 30 to 2000rpm speed is fitted.

The four main types of headstocks are

· Step cone pulley driven headstock.

· Direct electric motor driven headstock .

· All geared headstock.

· Pre-selective headstock.

3.TURRET HEAD AND SADDLE

The turret head is mounted on the ram fitted with turret slides longitudinally on the saddle. Turret head has a hexagonal block having six faces with a bore for mounting six or more than six tools at a time. The threaded hole on these faces are used to hold the tools. The actuation of ram is done by hand or power. An adjustable stopper is used to control the forward movement of the ram. Ram is returned to its initial position in order to index the cutting tool. The tools are indexed to 60 by rotation of circular plate which is indexed automatically along with the turret head. For bringing the next tool into cutting position a mechanism called Geneva mechanism is used.

01 - capstan lathe turret head and saddle

It is an H shaped component fitted across the lathe bed. It moves along the guide way. It can be moved anywhere along the bed and locked to the required position. In capstan lathe the turret head is mounted upon the ram which slides upon the saddle.

4.CROSS SLIDE

There are two type of cross slides they are

· Reach over type

· Slide hung type

Reach over type

The cross slide has two tool posts having totally four faces of square turret for mounting the tools. Tools are indexed by an angle of 90. While indexing, the motion of each tool is controlled by stop bars.

Slide hung type

This type of cross slide is entirely supported on the front and has no rear tool post. This enables a greater swing capacity to hold large diameter workpiece.

WORKING PRINCIPLE

Work piece is held in collet or chucks which is actuated hydraulically or pneumatically. All the needed tolls are held in the respective holes on the turret head. According to the sequence of operation the tool is moved with the help of turret head.

· Drilling, boring, turning, reaming, threading tools are mounted on the turret head.

· Forming, chamfering, knurling tools are mounted on the front end of the turret.

· Parting tool is mounted in inverted position on the rear end of the turret.

After completing each operation the turret head is moved back to its initial position which indexes the tools automatically.

ADVANTAGES

· Rate of production is higher.

· Different ranges of speeds are obtained.

· More number of tools can be accommodated.

· Chucking of larger work pieces can be done.

· Operators of less skill is required hence lowers the labour cost.

· Higher rigidity so can withstand heavy loads.