The Technique of Lapping
Pressure plates are also an important part of the lapping process, performing the following functions:
- Pressing uneven or rough workpieces against the lapping plate (felt or rubber pads).
- Obtaining acceptable parallelism of the top and bottom faces of the parts by means of the perfectly flat bottom of the pressure plates without pads.
For parallelism, the contact surface of the pressure plate should be perfectly clean, and the lapping fluid should be uncontaminated and form a uniform film. It is also advantageous to interchange the workpieces diagonally from time to time.
Cast iron, steel or aluminum are suitable as materials. Aluminum has proven to be suitable in the case of frequent handling. However, additional pneumatic loading is required in this case to permit economical work.