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Type of work holding devices being used on lathe
This article describes about the work holding devices which are required to hold devices on a Lathe. Read this article to know about Carriers and catch plates, Face plates, Angle plates, Mandrels, Rests and other related information.
Work holding devices on a lathe
As we know the lathe is one of the oldest and highly important machine tool. There is vast number of applications of this machine tool. So for facilitating the easy machining of the work piece it should be held tightly and securely. For this purpose many types of accessories are being used for facilitating easy holding of the work piece.
Some of the work holding devices are
1) Carriers and catch plates
2) Face plates
3) Angle plates
Carriers and catch plates
These are in general used for driving the work piece when it is held in between two centers namely head stock and tail stock. Carriers are also called as the driving dogs. These are attached to the work piece by the help of setscrews. Where as the catch plates are pinned to the headstock.
Faceplates are used for holding those work pieces, which cannot be held both by centers and by chucks. The construction of the faceplates is very simple. It consists of a center bore and plain and radial slots through the plate for facilitating the holding of the work piece. The central bore has a radius equal to that of the radius of the spindle of the lathe. And the plain and radial slots provide a healthy platform for holding the jobs by using T-bolts and clamps.
These are used along with faceplates for maintaining the given work piece horizontal i.e. perpendicular to the tool used. Angle plates consist of two faces, which are highly machined, and these also have the provision of holes for the easy clamping of the work piece to it.
This type of work holding devices are employed for holding previously drilled or bored hole so as to facilitate effective outer surface machining. The work is loaded over the mandrels between the centers. The ends of the mandrels are made slightly smaller than the original diameter. This is done for effective gripping of the mandrel in the chuck or any other holding device. In general the material used for the manufacturing of the mandrels is plain carbon steel. Various types of mandrels are in usage. Various types of mandrels are
1) Plain mandrels
2) Step mandrels
3) Collar mandrels
4) Screwed mandrels
5) Cone mandrels
6) Gang mandrels
7) Expansion mandrels
This type of mandrels finds a numerous number of applications in shops where identical pieces are to be generated. The body of these mandrels has generally a tapered shape. The difference in the tapped diameter is of 1 to 2 mm and the length varies between 55mm to 430mm. the tapper is provided for facilitating high end gripping for holding the work piece.
A special type of mandrel, which facilitates faster processing’s by holding various sized jobs with out replacing the mandrel. This type of mandrels finds applications in repair shops and generally used for turning collars, washers and odd sized jobs.
A collar mandrel has a collar arrangement, which is fixed and may have size larger than that of the 100mm. this type of construction is a type of optimizing the material being used.
These mandrels have a thread cut engraved on one side along with a collar. Such type of mandrels is called as screwed mandrels. Screwed mandrels are used when work pieces having internal threads are to be machined. The size of the threads to be engraved on the screwed mandrels depends on the type of work piece, which is going to fit over it.
Cone mandrels have a cone shaped piece attached at one of the mandrel. This type of arrangement allows the mandrel to handle a variety of work pieces having a varying internal crossectional diameter. The work piece is held tightly by fixing a nut at the other end of fixing the work piece to the mandrel. Too tight fitting of the work piece over the cone may damage the internal surface finish of the work piece along with the damage to the cone shape of the mandrel.
Gang mandrel is generated by some of the optimizers so as to reduce the material. This type of mandrel can facilitate machining for work pieces of various diameters. The gang mandrels consist of a fixed collar at one end and removable mandrels at the other end which is fixed by the help of the threads engraved both on the mandrel and also on the internal surface of a hallow mandrel. This mandrel can be used for machining various diameter pieces by just removing and fixing various collars over the thread. The friction between the walls of collar and sides of work piece is enough to hold the work piece tightly and hence facilitating is a high end machining.
This is a special type of mandrel, which has a central tapered pin. Over this tapered pin a sleeve is arranged when this sleeve is moved over it form one corner to other the size increases or decreases. This type of mandrels is best used when a varying diameter pieces are to be hold without much difficulty.
A chuck is a work holding device. It is used for holding work over a lathe machine, which is having large length and small diameter, and also for jobs, which are unable to mount on between the centers i.e., head stock and tail stock centers. A chuck is also employed when a non-axis symmetrical object is to be mounted over the lathe. The chucks are most commonly used work holding devices. These are fixed directly to the spindle of the lathe by means of screws and a back plate. In general there are various types of chuck, which have their own importance and unique applications
Types of chucks
• Four jaw chuck or independent chuck
• Three jaw chuck or self-centering chuck
• Air or hydraulic operated chuck
• Magnetic chuck
• Collet chuck
• Combination chuck
• Drill chuck
Four jaws or independent chuck
As the name indicates this chuck has four jaws for holding the work each jaw is independent to move.
a. Any type of work piece can be held easily
b. High grip is possible as four jaws are employed
a. Centering is a little difficult process
b. Semi skilled labor are required
Three jaw chuck (or) self centering chuck
Three jaw chuck or self-centering chuck is the chuck, which has three jaws for holding the work piece, and if one jaw is moved then all the other jaws also move by same distance. This mechanism is obtained by engaging pinions which meshes with the teeth cut on the under surface of the chuck. This chuck is also called
a. Centering process is not necessary as all the jaws moves at a time
b. Consumes less time for mounting and un mounting the work piece.
a. Grip is not so high as only three jobs are employed
b. All type of jobs cannot be mounted on these chucks, as they are useful in machining only axis symmetrical objects
As the name indicates it is a combination of both three-jaw chuck and four-jaw chuck. It acts as both self-centering and independent chuck. This is obtained by engaging a scroll disc at the backside of jaws.
In this chuck magnetic force is used for holding the work piece.
• Work pieces in which damage due to the jaws of chucks is not tolerated can be effectively machined by using this chuck
• If the work to be held is of very small size and cannot be hold by the above three chucks then this chuck can be used
a. All type of jobs cannot be held
b. Size of the job affects the efficiency of the holding
c. All type of materials cannot be held as it works on magnetic property only magnetic materials can be held.
This type of chuck is used when the work to be held is very long in size.
Air or hydraulic operated chuck
This is also called as pneumatic chuck as it is being operated by hydraulic or air energy. This chuck holds the work piece due to the pressure generated in the cylinder.
This chuck is used for holding the tool in the drilling machines. This also plays a role in holding taper shanks on a lathe for easy machining of the job on which holes are to be drilled.
Rest is a work holding device, which is used to hold the work piece when the work piece of very long length are to be held. In general when a long piece is to be held it may have directly held then there arises deflection in the work piece due its own weight. So to prevent the deflection in the work piece rests of various types are used. Some of the rests being used are
1) Steady rest
2) Follower rest
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