Types Of Chuck In Lathe Machine
Introduction to Types of chuck in lathe machine:
A chuck is one of the most important devices for holding and rotating a piece of work in a lathe.
The workpiece of short length and large diameter of irregular shape which cannot be conveniently mounted between centres are held quickly and rigidly in a chuck.
A chuck is attached to the lathe spindle by means of bolts with the back plate screwed on to the spindle nose. Accurate alignment of the chuck with the lathe axis is effected by spigotting.
Types of Chuck in Lathe Machine are as follows:
- Four jaws independent chuck
- Three jaws universal chuck
- Combination chuck
- Magnetic Chuck
- Collet chuck
- Air or hydraulic operated chuck
- Drill Chuck
Four-Jaw independent chuck:
The figure shows a four jaw chuck diagram. The arrangement of four jaws independent chuck, which has four jaws, located at an angle of 90° to each other.
Here all the four jaws are opened independently. Here four screws are used in place of scroll disk, Hence it is called as four jaw independent chuck.
Each jaw made of tough steel has three inner and one outer gripping surface. The outer gripping surface is used for holding larger sizes of the workpiece by reversing the jaw.
Concentric circles inscribed on the face of the chuck facilitate quick centring of the workpiece. This type of chuck is particularly used in the setting up of heavy and irregular shaped articles. The diameter of the body specifies the size of the chuck.
Universal or Three Jaw Chuck:
A three-jaw chuck is shown in the figure. This is the most commonly used types of chuck in lathe machine. The three jaws are generally made of high-quality steel and are arrogated at an angle of 120° to each other.
During the operation, the jaw teeth are made to mesh with scrawl spiral teeth (Bevel teeth). The meshing causes a moment of all three jaws either towards or away from the chuck centre, depending upon the direction of rotation of the bevel pinion. The pinion is operated by square end key called “chuck key”.
The chuck suitable for holding round, or hexagonal, and other similar shaped workpieces. In three jaw chuck, the job is centred automatically and quickly. But it has the less gripping capacity as only three jaws are used and centring accuracy is soon lost due to wear.
As the name implies, a combination chuck, as shown in Figure. It is used both as a self-centring and an independent chuck to take advantage of both the types.
The jaws is operated individually by separate screws or simultaneously by the scroll disc. The frame has teeth cut on its underside which meshes with the scroll and all the jaws together with the screws move radially when the scroll is made to rotate by a pinion.
The chuck is used for holding a very thin workpiece made of magnetic material which cannot be held in an ordinarily chuck. It is also used where any distortion of the workpiece due to the pressure of the jaws is undesirable.
The holding power of the chuck is obtained by the magnetic flux radiating either from the electromagnets or from the permanent magnets introduced within the chuck.
In the ON position, the flux passes through the workpiece and grips it. In OFF position the magnets are set aside bringing them in contact with high permeable ” keepers” which short-circuit the flux and prevent them from passing through the workpiece.
Collet chucks are used for holding bar stock in production work where quick setting and accurate centring is needed.
The chuck attached to the spindle by a nut consists of a thin cylindrical bushing known as collet having a slots cut lengthwise on its periphery. The inside bore of the collet is cylindrical, hexagonal, square, etc. Depending on the shape of the work that will pass through it.
The outside surface of the collet which is tapered fits in the taper hole on the body of the chuck, and the tail end which is threaded meshes with a key.
When the key is turned from outside, the collet is drawn in resulting the split tapered end to be pushed inward due to the springy action. And the workpiece is securely and accurately held in the chuck. Different sizes of collectors are used for holding different sizes of the bar stock. These chucks are commonly used in capstan and turret lathes.
Air or hydraulic operated chucks:
This type of chuck shown in the figure. It is used in mass production work for its fast and effective gripping capacity.
The mechanism incorporates a hydraulic or air cylinder mounted at the back end of the headstock spindle and rotates with it.
Fluid pressure is delivered to the cylinder by operating a valve with a lever and the piston will slide within the cylinder. The movement of the piston is transmitted to the jaws by a connecting rod and links and the jaws grip the workpiece securely.
A drill chuck is sometimes used in a lathe for holding straight skank drill, reamer or tap for drilling, reaming, or tapping operation. The chuck is held either in headstock or tailstock spindle. It has centring jaws which have operated by rotating a key.
Difference between Three jaws and Four-jaw chucks:
1. The jaws on the three jaw chuck move all at the equal time. On four jaws chuck, jaws move separately.
2. The depth of cut is relatively less in three jaw chuck. In four jaw chuck, the higher depth of cut can be produced.
3. The three Jaw chuck has one hole for the chuck key to tighten or loosen the jaws’ grip. Four-Jaw chuck has four holes for the chuck key to controlling each jaw at one time.
4. In three jaw chuck, the workpieces cannot be set for eccentric turning. But in four jaw chuck, the workpieces can be set for eccentric turning.
5. In three jaw chuck centring accuracy is lower. But in four jaw chuck centring accuracy better than a three jaw chuck.
6. Three jaw chuck has less gripping power than four jaw chuck.
7. In three jaw chuck, heavier workpieces cannot be turned. In four chuck heavier workpieces can be turned.
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