Carpentry may be defined as the process of making wooden components. It starts from a marketable form of wood and end with a finished product. It deals with the building work, furniture, cabinet making, etc. Joinery, i.e., preparation of joints in one of the important operations in all wood-works. It deals with the specific wood of a carpenter like making different types of joints to form a finished product.
Welding is the process of joining similar metals by the application of heat, with or without application of pressure or filler metal, in such a way that the joint is equivalent in composition and characteristics of metals joined. In the beginning, welding was mainly used for repairing all kinds of worn or damage parts. Now, it is extensively used in manufacturing industry, construction industry (construction of ships, tanks, locomotives and automobiles) and maintenance work, replacing riveting and bolting, to a great extent.
- The various welding processes are:
- a. Electric arc welding,
- b. Gas welding,
- c. Therrmit welding,
- d. Resistance welding, and
- e. Friction welding.
However, only electric arc and gas welding are here. In either process, the work pieces are melted along a common edge, to their melting point and then a filler metal is introduced to form the joint on solidification. The materials to be welded must be free from rust, scale, oil or other impurities, so as to obtain a sound weld.
In machine shop, metals are cut to shape on different machine tools. A lathe is used to cut shape the metal by revolving the work against a cutting tool. The work is clamped either in a chuck, fitted onto the lathe spindle or in-between the centres. The cutting tool is fixed in a tool post, mounted on a movable carriage that is positioned on the lathe bed. The cutting tool can be fed into the work, either lengthwise or cross-wise. While turning, the chuck rotates in countered-clock wise direction, when viewed from the tail-stock end.
In machine shop, a shaping machine or shaper is used for producing flat (plane) surfaces, which may be horizontal, vertical or inclined. In shaping work, a single point tool, similar to lathe tool, is given a reciprocating motion with the help of a mechanism provided in the machine that converts rotary motion into reciprocating motion. The shaper receives power by an individual motor either through gear drive or belt drive.
Machine tool is capable of producing work at a faster rate, but, there are occasions when components are processed at the bench. Sometimes, it becomes necessary to replace or repair a component which must fit accurately with another component on re-assembly. This involves a certain amount of hand fitting. The assembly of machine tools, jigs, gauges, etc., involves certain amount of bench work. The accuracy of work done depends upon the experiences and skill of the fitter.
It deals with the process of making castings in moulds, formed in either sand or some other material. The process involves the operations of pattern making, sand preparation, molding, melting of metals, pouring in moulds, cooling, shake-out, fettling, heat treatment, finishing and inspection.
Mould is a cavity formed by a pattern. It is similar in shape and size to that of the actual casting plus some allowance for shrinkage, machining, etc. Molding is the process of making moulds.
Moulds are classified as temporary and permanent. Temporary moulds are made of refractory sand and other binding materials and may be produced either through hand molding or machine molding. Permanent moulds are made of ferrous metals and alloys, i.e., cast iron, steel, etc.