Lathe Operations: Facing

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Facing Operations Facing is the process of removing metal from the end of a workpiece to produce a flat surface. Most often, the workpiece is cylindrical, but using a 4-jaw chuck you can face rectangular or odd-shaped work to form cubes and other non-cylindrical shapes.

When a lathe cutting tool removes metal it applies considerable tangential (i.e. lateral or sideways) force to the workpiece. To safely perform a facing operation the end of the workpiece must be positioned close to the jaws of the chuck. The workpiece should not extend more than 2-3 times its diameter from the chuck jaws unless a steady rest is used to support the free end. Cutting Speeds

If you read many books on machining you will find a lot of information about the correct cutting speed for the movement of the cutting tool in relation to the workpiece. You must consider the rotational speed of the workpiece and the movement of the tool relative to the workpiece. Basically, the softer the metal the faster the cutting. D…

Atomic Arrangement in Metals

A metal can exist in the gaseous, liquid or solid states depending upon the pressure and temperature. Metals have the ability to donate electrons and form a positive ion. Metals have high density, high melting temperature, good electrical and thermal conductivity, metallic lustre and crystalline structure.



Structure of Solids - On the basis of structure, solids are broadly classified as:



(a) Amorphous Solids. These are solids where the atoms making up the crystal are not arranged in a systematic order. Examples of amorphous solids are wood, plastic, glass, rubber etc.



(b) Crystalline Solids.These are solids where the atoms making up crystals are arranged in a systematic order. Examples of crystalline solids are: Iron, Copper, Aluminium, Zinc and Nickel, etc.



Space Lattice and Unit Cell



In a crystal, the atoms are arranged in a periodic and regular geometric pattern in space. The arrangement of atoms in a crystal can be described with respect to a three dimensional net of straight lines, called space lattice. The intersections of lines are points of a space lattice. The important characteristic of a space lattice is that every point has identical surroundings.



Unit Cell - The number of atoms which constitute a crystal is very large and even the smallest crystals are composed of billions of atoms. The grouping of atoms, whose repetition will produce the crystal is called the unit cell. A unit cell is a building block of the crystal.



Lattice Parameters of a Unit Cell



The edges of unit cell (i.e., length, breadth and height) a, b, c are called primitives and the three angles α, β, γ are known as interfacial angles of a unit cell



These three edges (a, b, c) and three interfacial angles (α, β, γ ) of the unit cell are called lattice parameters or geometrical constant of a crystal system, made up of such unit cells.

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