The Lapping Oil

The fluid used in the lapping medium must be chosen carefully. Oil viscosity is critical to the efficiency of the process. If the fluid (e.g. oil) is too viscous, the film between the lapping plate and workpiece is very thick. Also, if the particles are too small, their tips protrude insufficiently from the film. If the film is too thin, it may rupture and allow metal-to-metal contact between the working plate and the workpiece. This can potentially cause unfixable damages on the workpiece surfaces. An excessively greasy medium is inefficient. Therefore, removing the abraded material from the lapping area needs to happen immediately. (This is comparable to the flow of swarf during machining.)

The lapping oil carries the lapping powder or diamond products and distributes the particles evenly over the lapping plate. It helps prevent grooves and scratches on the workpiece and reduces the temperature of the process. The oil also transports removed material into the lapping plate slots or to the edge of the plate.

Rule-of-thumb:

Large lapping grains – thick medium film
Small lapping grains – thin medium film

Wrong or untested lapping fluids can lead to a great time and quality loss. Inadequate or irregular rotation of the conditioning rings due to incorrect lapping agents has serious consequences for the correction effect on the working plate (also see Page 8-15).