Lapping:

It is an abrading process that is used to produce geometrically true surfaces, correct minor surface imperfections, improve dimensional accuracy, or provide a very close fit between two contact surfaces. Very thin layers of metal are removed in lapping and it therefore evident that lapping is unable to correct substantial errors in the form and sizes of surfaces. It is, however a low efficiency process and is used only when specified accuracy and surface finish cannot be obtained by other methods.

Laps may be operated by hand or machine, the motion being rotary or reciprocating cylindrical work may be lapped by rotating the work in lathe or drill press and reciprocating the lap over the work in an ever changing path. Small flat surfaces may be lapped by holding the work against a rotating disc, or the work may be moved by hand in an irregular path over a stationary faceplate lap.

Honing:

It is grinding or an abrading process mostly for finishing round holes by means of bonded abrasive stones, called hones. Honing is therefore a cutting operation and has been used to remove as much as 3mm of stock but is normally confined to amounts less than 0.25mm. So honing is primarily used to correct some out of roundness, taper, tool marks and axial distortion. Honing stones are made from common abrasive and bonding materials, often impregnated with sulphur or wax to improve cutting action and lengthen tool life. Materials honed range from plastics, silver and cast iron to hard steel and cemented carbides. This method is mostly used for finishing automobile crankshaft journals.

When honing is done manually the tool is rotated, and the work piece is passed back and forth over the tool. For precision honing, the tool is given a slow reciprocating motion as it rotates. It is done on general purpose machines, such as the lathe, drill press, and portable drills, as an expedient. But more economical results can be obtained by honing machines for production work. Coolants are essential during this process to keep the operation temperatures uniform and wash away the chips.