The objective of this study is to determine the effects of bedding plane orientations and scratching directions on the CERCHAR Abrasivity Index (CAI) of various rock types, including Khao Khad argillaceous limestone, Khao Khad bedded limestone, Phu Kadueng sandstone, Phu Phan sandstone and Tak Fa gypsum. The ploughing forces and groove volumes are also investigated. The results indicate that higher CAI values and ploughing forces are observed in stronger rocks (limestones and sandstones) compared to softer rocks (gypsum). The groove volume increases as the CAI value decreases for all tested specimens. Higher CAI values are obtained for hard rocks when the scratching direction is opposite to the dip direction of the bedding planes. The highest CAI values are observed when the stylus pin moves perpendicular to the bedding trend, rather than along the bedding planes. The effect of bedding plane orientation on CAI is more pronounced in strong rocks than in soft ones. These findings will play an important role in maintaining drill bit lifetime, especially within rock types with varying bedding planes.