Part 1 basic guide to polishing

Polishing techniques

How we produce a mirror finnish is down to hard work, skill and a little common sense.
Take aluminium, its a very dirty material to work with, producing lots of black dust when being polished, but the end result and sense of pride far outways the hard work and sweat put into it. Just patience and commitment is all thats needed.
To get a show like finish or show finish, well thats a whole new ball game.

So what is a mirror finnish? If you were to look at a mirror finish under a microscope it would look like a mountain range. But because the peaks and valleys are so small and close together and rounded off, they reflect light and the surface appears smooth and mirror like, although its not.
Absolute flatness is actually impossible to achieve but we can get pretty close. therefore all we are actually doing is making a series of finer and finer scratches untill we eventually round of the peaks. This is achieved by going through the abrasive grades untill we get to the finish we want. The three methods used are: Abrasive finishing polishing, Buffing or bright finishing and colouring.

The first stage is often described as 'emery bobbing' or 'scurfing' this involves the use of abrasives which cut away the surface irregularities and imperfections. It can also be done by the use of abrasive belts, flap wheels, hand rubbing blocks or abrasive cloths and papers.

The second stage is polishing or buffing and requires the use of polishing compositions and mops to produce a bright smooth finish. The term COLOURING is applied to the final polishing of metal part when again use is made of mops and polishing compositions. After all the scratches have been polished out the metal is finally 'coloured' . To make it clean and brilliant, a lime-based or rouge composition is used on the finishing mops.

ABRASIVES

There are three main abrasives which we use, emery, aluminium oxide and silicon carbide, aluminium oxide being the most popular. The abrasives can be obtained in various grit sizes, from flour which is the finest and comes in 1200 and 1000, right through to the most common of 320 and so on till it reaches 60 or sometimes can be coarser. For abrasive finishing we only need grit sizes 320 to 60.
Abrasives are used in metal finishing in the following ways:: On abrasive belts, flap wheels, cloths and papers, etc.: On dressed wheels, mops, felt bobs, etc.: In grease bonded and lime-based polishing compositions: Loose grains for grit blasting, vapour blasting and lapping, in flexible rubber polishing blocks, sticks, polishing wheels and mounted point .Abrasive belts and flap wheels are now extensively used for preliminary abrasive operations prior to the polishing of components.is made up of strips of aluminium oxide coated belt material and bonded circumfrentially around a central resin core which is mounted on a steel shaft. This can be used on any D.I.Y. electric drill and hey presto you have a portable abrasive finishing machine which can be taken anywhere there is a power outlet.The abrasive flap wheel has all the advantages of the abrasive belt machine but with none of the disadvantages of high cost, non-portability, size and inability to work in small internal recesses.

ABRASIVE DRESSED WHEELS
The wheels or bobs are dressed with abrasive grain (emery, aluminium oxide or silicon carbide) using glue or cement as adhesive. Felt bobs are the most popular wheel used commercially, for their long life, although they are quite expensive, Felt wheels can be turned to any shape to suit particular trades or duty, such as grooved bobs for tubular work, small cones and fingers for jewellery and knife edged.

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