Turning (Lathe)

Turning Machine

What is Turning Machine?

Turning is a form of machining, a material removal process, which is used to create rotational parts by cutting away unwanted material. The turning process requires a turning machine or lathe, workpiece, fixture, and cutting tool. The workpiece is a piece of pre-shaped material that is secured to the fixture, which itself is attached to the turning machine, and allowed to rotate at high speeds. The cutter is typically a single-point cutting tool that is also secured in the machine, although some operations make use of multi-point tools. The cutting tool feeds into the rotating workpiece and cuts away material in the form of small chips to create the desired shape.

Turning Proccess

Turning is used to produce rotational, typically axi-symmetric, parts that have many features, such as holes, grooves, threads, tapers, various diameter steps, and even contoured surfaces. Parts that are fabricated completely through turning often include components that are used in limited quantities, perhaps for prototypes, such as custom designed shafts and fasteners. Turning is also commonly used as a secondary process to add or refine features on parts that were manufactured using a different process. Due to the high tolerances and surface finishes that turning can offer, it is ideal for adding precision rotational features to a part whose basic shape has already been formed.

History Lathe (Turning Machine)

The first lathe machine that was ever developed was the two-person lathe machine which was designed by the Egyptians in about 1300 BC. Primarily, there are two things that are achieved in this lathe machine set-up. The first is the turning of the wood working piece manually by a rope; and the second is the cutting of shapes in the wood by the use of a sharp tool. As civilizations progressed, there have been constant modifications and improvements over the original two-person lathe machine, most importantly on the production of the rotary motion.

The production of the rotary motion therefore evolved according to the following procedures: the Egyptians manual turning by hand; the Romans addition of a turning bow; the introduction of the pedal in the Middle Ages; the use of the steam engines during the Industrial Revolution; the employment of individual electric motors in the 19th and mid 20th centuries; and the latest of which is the adaption of numerically controlled mechanisms in controlling the turning machine as name CNC Machine.

Parts of Turning Machine

Turning machine parts

Bed

The bed of Lathe acts as the base on which the different fixed and operations parts of the Lathe are mounted. Lathe beds are usually made as single piece casting of semi-steel (i.e., toughened cast iron),with the addition of small quantity of steel scrap to the cast iron during melting; the material ‘cast iron’ facilitating an easy sliding action. In case of extremely large machines, the bed may be in two or more pieces, bolted together to from the desired length.

Tool post

It is bolted on the carriage. It is used to hold the tool at correct position. Tool holder mounted on it.

Chuck

Chuck is used to hold the workspace. It is bolted on the spindle which rotates the chuck and work piece. It is four jaw and three jaw according to the requirement of machine.

Head stock

Head stock is the main body parts which are placed at left side of bed. It is serve as holding device for the gear chain, spindle, driving pulley etc. It is also made by cast iron.

Tail stock

Tail stock situated on bed. It is placed at right hand side of the bed. The main function of tail stock to support the job when required. It is also used to perform drilling operation.

Lead screw

Lead screw is situated at the bottom side of bed which is used to move the carriage automatically during thread cutting.

Legs

Legs are used to carry all the loads of the machine. They are bolted on the floor which prevents vibration.

Carriage

It is situated between the head stock and tail stock. It is used to hold and move the tool post on the bed vertically and horizontally. It slides on the guide ways. Carriage is made by cast iron.

Apron

It is situated on the carriage. It consist all controlling and moving mechanism of carriage.

Chips pan

Chips pan is placed lower side of bed. The main function of it to carries all chips removed by the work piece.

Guide ways

Guide ways take care of movement of tail stock and carriage on bed.

Speed controller

Speed controller switch is situated on head stock which controls the speed of spindle.

Spindle

It is the main part of lathe which holds and rotates the chuck.

Turning Operations

a variety of operations may be performed to the workpiece to yield the desired part shape. These operations may be classified as external or internal. External operations modify the outer diameter of the workpiece, while internal operations modify the inner diameter. The following operations are each defined by the type of cutter used and the path of that cutter to remove material from the workpiece.

External operations

Turning

turning operation
turning operation

A single-point turning tool moves axially, along the side of the workpiece, removing material to form different features, including steps, tapers, chamfers, and contours. These features are typically machined at a small radial depth of cut and multiple passes are made until the end diameter is reached.

Facing

facing operation
facing operation

A single-point turning tool moves radially, along the end of the workpiece, removing a thin layer of material to provide a smooth flat surface. The depth of the face, typically very small, may be machined in a single pass or may be reached by machining at a smaller axial depth of cut and making multiple passes.

Grooving

grooving operation
grooving operation

A single-point turning tool moves radially, into the side of the workpiece, cutting a groove equal in width to the cutting tool. Multiple cuts can be made to form grooves larger than the tool width and special form tools can be used to create grooves of varying geometries.

Cut-off (parting)

cutoff operation
cutoff operation

Similar to grooving, a single-point cut-off tool moves radially, into the side of the workpiece, and continues until the center or inner diameter of the workpiece is reached, thus parting or cutting off a section of the workpiece.

Thread cutting

thread cutting operation
thread cutting operation

A single-point threading tool, typically with a 60 degree pointed nose, moves axially, along the side of the workpiece, cutting threads into the outer surface. The threads can be cut to a specified length and pitch and may require multiple passes to be formed.

Internal operations

Drilling

drilling operation
drilling operation

A drill enters the workpiece axially through the end and cuts a hole with a diameter equal to that of the tool.

Boring

boring operation
boring operation

A boring tool enters the workpiece axially and cuts along an internal surface to form different features, such as steps, tapers, chamfers, and contours. The boring tool is a single-point cutting tool, which can be set to cut the desired diameter by using an adjustable boring head. Boring is commonly performed after drilling a hole in order to enlarge the diameter or obtain more precise dimensions.

Reaming

reaming operation
reaming operation

A reamer enters the workpiece axially through the end and enlarges an existing hole to the diameter of the tool. Reaming removes a minimal amount of material and is often performed after drilling to obtain both a more accurate diameter and a smoother internal finish.

Tapping

tapping operation
tapping operation

A tap enters the workpiece axially through the end and cuts internal threads into an existing hole. The existing hole is typically drilled by the required tap drill size that will accommodate the desired tap.

How To Operating Turning Machine

  1. A cylindrical work piece fixed to the chuck. A chuck may have three jaw or for jaw according to the requirement. The work piece is at the center or some eccentric according to the process perform.
  2. The spindle starts to rotate and set it at desire speed. The spindle speed plays a huge role during cutting. The spindle rotates the chuck and work piece.
  3. Now check the work piece is turning properly. If it not set the work piece using dial gauge.
  4. Now set the tool at desire feed by moving the tool post and carriage. The feed also play main role during cutting. Large feed may cause unwanted temperature increase.
  5. After it tool is introduce between moving work piece at desire feed rate. It cut the metal from work piece. The feed rate is set at the cutting condition.
  6. Now all unwanted metal is removed by moving the carriage form horizontally and vertically as desire according to the job requirement. After complete all process we got a well finished job.
  7. Turning machine can perform turning, boring, chamfering, shaping, facing, drilling knurling, grooving as shown in figure turning operations.

Source :

  • www.brighthubengineering.com
  • www.custompartnet.com
  • wikipedia.org
  • engineeringinsider.org

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