Marking off or layout is carried out to indicate the locations of operation to be done, and provide guidance during rough machining or filing.
The line marked on metal surfaces is likely to be erased due to handling. To avoid this, permanent marks are made by placing punch marks at convenient mark intervals along the marked line. Punch marks act as a witness against inaccuracies in machining and hence, they are known as witness marks.
Marking off table
A marking table (marking-off table) is used as a reference
surface for marking on work-pieces.
Marking tables are of rigid construction with accurately finished top surfaces. The edges are also finished at right angles to the top surface. Marking tables are made of cast iron or granite, and are available in various sizes. These tables are also used for setting measuring instruments, and for checking sizes, parallelism and angles.
Care and maintenance of Marking off table
- A marking table is very precise equiment, and should be protected from damage and rust.
- After use, the marking table should be cleaned with a soft cloth.
- The Surface of the marking table, made of cast iron, should be protected by applying a thin layer of oil.