Lathe machine is probably the simplest machine tools used for the metal machining operation called turning. Turning is a metal working process of producing cylindrical shaped work pieces. A metal lathe can also be used for metal cutting operations like drilling, boring, reaming, tapping, knurling and thread cutting.
On a Metal Lathe, the work piece is rigidly held on the rotating head stock of the metal lathe using a chuck or a collet. The stationary cutting tool which is fixed on the carriage of the metal lathe is fed against the rotating work piece to remove the excess metal to produce cylindrical shaped work pieces. The work piece can also be held between centers (between head stock center and tail stock center) and transfer the movement of the rotating spindle to the work piece using a lathe dog.
Work Holding methods on a Metal Lathe
Following are the most common methods of work piece holding on a metal lathe.
1. Between centers
2. Independent chuck
3. Universal self centering chuck
Each of these working holding methods have its merits over the others. While working on metal lathes the right method of work holding need to be chosen depending upon the type of metal cutting operation, shape, size and accuracy of the work piece.
Types of Metal Lathes
Depending upon the construction of the lathe, metal lathes can be classified into Engine lathe, Mini lathe, Capstan lathe, Turret lathe and Cnc lathe. Engine lathes and mini lathes are mainly used for custom made parts while capstan and turret lathes are suitable in mass production of turned parts. CNC lathes can be used for both mass production as well as for custom jobs with complicated profiles on the round work piece.
Engine lathe is also known as center lathe. They can be used for almost all the lathe operations including turning, drilling, reaming, boring, thread cutting etc. The most common work holding method used in an engine lathe is between centers or a chuck. For longer work pieces turning between centers are advised. It is also possible to do taper turning in engine lathe by offsetting the tail stock center.
Parts that are shorter in length, irregular in shape and heavy are usually best machined in an independent chuck on engine lathe. In case of round work pieces a universal self centering chuck is the best way to go. Because it enables a fairly accurate and rapid location of the work piece for machining on engine lathe. The lead screw of the engine lathe which is connected to the carriage makes it possible to cut various types of threads on an engine lathe.
Small Metal Lathe
Mini lathe which is also as table lathe is a small metal lathe used for turning small and accurate jobs. This is a smaller version of the engine lathe but more accurate. Small metal lathe or mini lathe is the favorite of hobbyist and hence it is often called the hobby lathe. Usually collets and universal self centering chucks are used for holding the work pieces on mini lathe. In some of the small metal lathes it is possible to hold the work piece between centers where the small lathe is equipped with a mini tail stock.