It is also possible to use harder (RC 60) steel liners, by screwing or welding them to un- hardened beds [Fig. 5.37]. The latest trend is to coat beds with a thin layer of polymer by spraying, or gluing a thin film. The hardness along the guideway length, should not vary more than 25 BHN on a single bed, and 45 BHN for sectional beds.
5.2.3.1 Surface finish
Machining, grinding, lapping, and scraping are used to obtain the requisite surface finish and precision. An average number of bearing spots are measured over the entire slideway. It is customary to measure the contact spots on the bed by using a marking compound. The following table gives the number of spots for 25 sq. area, for various applications.