Lathe fixture is a device to ensure the accurate position of the workpiece and the reliable clamping of the workpiece. Usually supplied with the lathe. Lathe fixture can be generally divided into general fixture and special fixture two categories. Commonly used horizontal lathe clamp with chuck, face plate, center, drive plate, carrier, mandrel, steady rest and follow rest.
Chuck is the most widely used horizontal lathe fixture. It is mounted directly on the spindle of the lathe by the thread on the back flange. Used for clamping axis, disc, sleeve and other parts.
(1) 4-jaw chuck
4-jaw chuck is distributed symmetrically above four same claws, each claw can move independently, it is also called 4-jaw single chuck. A square wrench is used to rotate the screw behind a jaw, which can drive the jaw to move along the radial direction independently.
Clamping workpiece with 4- jaw chuck, when the workpiece diameter is large and must be clamping cylindrical, the jaw can be all reversed. And because each jaw can move single, so can be used for clamping irregular shape workpiece and eccentric workpiece.
The clamping force of 4-jaw chuck is larger, so it is especially suitable for rough machining and processing larger workpiece. The axis alignment of workpiece is carried out by using the single movement of jaw, but it is time-consuming and difficult to control the precision of alignment.
(2) 3-jaw chuck
3-jaw chuck has three apart 120° jaw, three jaws always open or close at the same time. The tightening force of three chucks is small and can not clamp irregular shaped parts, but it is quick and convenient, without alignment, with high automatic centering accuracy, especially suitable for small and medium-sized workpiece semi-finishing and finishing.
2. Face plate
It is suitable for some irregularly shaped workpieces which are not easy to be clamped by 3-jaw or four-jaw chuck. The face plate is mounted directly on the spindle. The work surface of the face plate has many radial guide grooves of different lengths, when used with Angle iron, pressure block, bolt, nut, pad block and balance iron, the workpiece can be clamped on the disc. Installation, according to the workpiece line mark alignment, and pay attention to the balance of the center of gravity, in order to prevent the rotation of vibration.
Face plate clamping workpiece
a) The workpiece is clamped on the face plate ; b)The workpiece is clamped by the face plate and the bending plate
1-pad; 2-pressing plate; 3-pressing plate screw; 4-T slot; 5-workpiece; 6-bending plate; 7-ajustable screw; 8-balance weight iron; 9- face plate
Center is divided into front center and back center. The front center is mounted in the spindle bore and rotates with the workpiece, without relative movement with the center hole.
Back center is installed in the tailstock sleeve, and there are two kinds of dead center and live center. During turning, the dead center and the hole in the center of the workpiece will heat due to sliding friction, and the center will be annealed at high speed. Therefore multi-purpose insert carbide top. Dead center advantage is good neutral rigidity, suitable for low - speed processing of high - precision workpiece.
Top small workpiece can be used with the reverse center live center and the workpiece rotation, reduce friction, suitable for high-speed cutting, it overcomes the shortcomings of the dead center, but there is a certain assembly error, so that the machining accuracy is reduced.
live center dead center
In order to ensure the coaxiality of shaft workpiece with longer or more processing procedures, two centers clamping methods are often adopted.
As shown in figure a)
The workpiece is supported between the front and back centers, and is rotated by clamp and drive plate. The front center is mounted in the spindle bore and rotates with the spindle. The back center is fixed in the taper hole of the tailstock. Sometimes, three-jaw chuck can be used instead of drive plate.
As shown in figure b).
At this time, the front center is made of a section of steel rod and clamped on the three-jaw chuck. The chuck's jaw drives the workpiece to rotate through the carrier.
a) Install the workpiece with two centers of the drive plate
b) Install workpiece with three jaw chuck instead of drive plate
4.Drive plate and carrier
The front and rear centers cannot drive the workpiece to rotate. When the workpiece is clamped with two centers, it must be driven to rotate by the drive plate and the carrier.
The drive plate is mounted on the spindle by screw thread. The drive plate drives the carrier to rotate. The workpiece and the carrier are fastened together by screws.
Mandrel is a commonly used fixture for processing disc and sleeve parts. According to its positioning surface, it can be divided into the following types:
The solid mandrel without stage has a taper of 1:1000 ~ 1:1500, which is characterized by simple manufacturing and high precision of parts processed. But in the length can not position, bear cutting force is small, loading and unloading is not convenient.
Press the workpiece with nut and washer, use the smaller gap between the inner hole and the mandrel cylinder to locate and process the outer circle. This kind of mandrel can install many parts at one time, but the machining accuracy is not high.
(3)Mandrel expansion force
The workpiece is tightened and turned by the expansion force generated by elastic deformation. When clamping, cover the workpiece on the mandrel, tighten the nut, make the open sleeve axial movement, the mandrel cone makes the sleeve cylindrical expansion, the workpiece can be firmly supported.
This kind of mandrel is convenient for loading and unloading, and can ensure the coaxiality of the workpiece, Suitable for small and medium parts processing.
6. Steady rest and follow rest
In the processing of slender shaft, because the rigidity of the workpiece is poor, easy to cause vibration and deformation, affect the processing accuracy. In order to increase the rigidity of the workpiece and prevent deformation, it is often used as the auxiliary support of the workpiece with steady rest or follow rest.