Post 174 –by Gautam Shah


Finishing surface of Pottery

Material finishing processes are employed essentially for changing the surface textural quality, by alteration, removal or addition. The Finishing processes may improve sensorial aspect (touch-feel-texture), look-colour-pattern, adhesion-wettability, weldability-solderability, corrosion resistance, tarnish resistance, chemical resistance, wear resistance, hardness, electrical conductivity, etc. An unfinished surface is often called mill finish. The finishing processes include acid-alkali treatment, chemical reactions, electro chemical deposition-removal (plating), mechanical procedures, burnishing, singeing, washing, coating, plastering, cladding, etc.


Of these processes GRINDING, POLISHING, HONING, LAPPING AND BUFFING, are briefly described here.


Grinding removes material from the surface to roughen a normally glossy surface like Glass, or polishes a rough surface like Stone. Grinding requires material of higher hardness than the surface material. Grinding is usually a step up or down procedure, using graded series of coarse to fine or fine to course abrasives. The grinding media or abrasives are of many types and forms, such as Carborundum, sandstone, emery, pumice, sand, glass and diamond powders, leather, jute, etc.

Brass polishing -an etching type of surface removal or ‘grinding’

Where a material constitution permits, very fine grinding may polish the surface. Grinding is also a cutting operation, where the material is cut or removed as minute chip, swarf or dust.


Grinding wheels usually consist of particles of a synthetic abrasive, such as silicon carbide or aluminum oxide, mixed with a vitrified or resinoid bonding material. Grinding can be coarse or fine, depending on the size of the grit used in the grinding wheel. Metal and glass can be ground to a mirror finish and an accuracy of 0.0000025 cm. Abrasive are used as grinding wheels, sandpapers, honing stones, polish, cut-off wheels, tumbling and vibratory mass-finishing media, sandblasting, pulp-stones, ball mills, and many other tools and products.


Stone surfaces are chiselled to split the material into thinner sections, to remove the weathered crust and also to level out the surface. Grinding and polishing is done to Hard materials such as building stones, marbles, granite, metals, glass; Precious and Semiprecious stones like gems, diamonds; Animal products like ivory, bones, horns, teeth, leather; Plant products like timbers, seeds; Ceramics like pottery products, bricks, cement concrete and other cement products.


Grinding-Finishing a Tri-suction RCC floor


Polishing uses extremely fine abrasive substances, such as jewellers rouge, Tripoli, whiting, putty powder and emery dust to rub or burnish an extremely smooth and brilliant finish on the surface of a material. The polishing materials are coated on the surface of cloth, felt, leather, rubber pr polymer wheels or as belts. Metal surfaces are levelled and finished by honing and lapping. Honing removes less than 0.0125 millimetres of material from the surface to eliminate micro scratches and machine marks from ground machine parts. It is done with bonded abrasive sticks or stones that are mounted in a honing head. Lapping is a process in which a soft cloth (wool, linen and chamois-leather) impregnated with abrasive pastes (rubbing compounds), is rubbed against the surface of a work-piece. Honing and lapping, are essentially metal finishing techniques. Buffing is a term used for polishing of metals. Buffing is done with polishing compounds and brushes of various shapes, and materials, likes: (animal hair, synthetic fibres, plant fibres -coir), flex, wool and leather. Barber polishing the razor on a leather stripe is a buffing process that levels out small nicks on the blade.

Barber’s Razor grinding stone and Honing leather straps

There are four types of precision grinding machines: Centre-type grinders used for tiny valve spools to steel mill roles. Centre-less grinders used for bowling balls, surgical sutures, and tapered roller bearings. Internal grinders are employed for inside diameters of gears, bearing races, and similar parts. Surface grinders are used for die tops, bench surfaces.


Lapping is used to produce a high-quality surface finish or to finish a work-piece within close size limits. Dimensional tolerances of 0.00005 millimetres can be achieved in the hand or machine lapping of precision parts such as gauges or gauge blocks.




Post -by Gautam Shah


Traditional street side grinding of knives and scissors


Metal abrading grinder

The first abrading tools were rough stones and hard grained abrasive sands. Tough fibres like asbestos, wool, and coir were also used for buffing purposes. Today sandpapers in sheet, stripes and tape forms are available with paper and cloth backing and bonded with water-based gums and synthetic resins. Carborundum and other man-made ceramic granules are embedded or cast in various base materials and shaped as discs, wheels, cones, rings, etc. for use with various machines. Such abrading tools are also used for drilling, edge dressing, tunneling, boring, etc.


Abrading stones are used to grind, de-husk and surface polish the food grains, nuts and seeds. This is done by pounding or by milling between stones. Nails, Screws, Nut-bolts, Toffees and sugar coated pills are rotated in drums to polish the surface.


Automobile and other lacquer finishes are buff-polished with very fine abrading media mixed with wax and silicon oil-based rubbing compounds. Abrading materials are also included in soft articles used in household utensil cleansers and jewellers polish to the hardest known material, the diamond. Leather, Jute, Linen, Chamois and may other materials with harder fibers are used for rubbing and polishing. Abrasives are used in the form of tumbling and vibratory mass-finishing media as for polishing for nails, sandblasting, flour mill stones, ball mills. Spectacle lenses and telescope lenses are ground with a abrading and then polishing media.



Hubble Telescope lens grinding

Abrasive materials and tools can cut through hardest materials at a faster speed than metal saws, while generating less heat and providing smoother cut face. New hard alloys and ceramics can only be cut by abrasives. Granite, marble, slate, and highly vitrified tiles are cut to size with diamond abrasive wheels. Grooves for expansion joints in runways and roads, holes in RCC structures are made by metal blades with embedded diamond abrasives. Metal components are cleaned by grinding tools of wire or hair wheels or by sand blasting.

Files of Different grains


FILES: Files are abrading tools. Files are of many different cross sections, lengths, notch configurations and the coarseness of the cut (density -teeth per area). A file could be very thin, almost like a knife with a serrated cutting edge, to a wide chequered figured plate. The most common sections are rectangular, triangular, round and half round. Most files have reduced size of section at their tail end. There are three tooth forms: The single-cut file has rows of parallel teeth that cut diagonally across the working surfaces. The double-cut file has rows of teeth crossing each other. Rasp teeth are disconnected round top notches. Rasp files, or rasps, are usually very coarse and are used primarily on wood and also soft materials like leather, aluminium, lead, etc. Files are used for many different purposes: to smoothen nails, cut injection vials of glass, removing human skin blemishes and birthmarks, for shaping bones during plastic surgery, removing spots and discolourations from suede fabrics, and for levelling teeth.

Grinder brush of Metal or Hair

Milling Machine Control Joinery Industry Carpenter