Premature failure of a diamond-coated tool often results from a poor adhesion of the coating and shortens the lifetime of the tool. This study presents the results of increasing the adhesion strength of diamond coatings on cutting tool inserts by pretreating the inserts with sandblasting technique to obtain a desirable surface morphology of the inserts. A geometric model representing the ideal surface morphology is established to enhance the nucleation density and adhesion strength of diamond coatings. Diamond coating experiment is conducted on the substrates of four different sample groups. Indentation and wear tests are performed on diamond-coated inserts to evaluate the effect of sandblasting on the adhesion strength of the coatings. A theoretical analysis is provided on the formation and growth of atom clusters in terms of the contact angle and the thermodynamic barrier of a substrate to predict diamond nucleation. The theoretical prediction has a good agreement with the experimental results obtained in this study and by Dennig and Stevenson [P.A. Dennig, D.A. Stevenson, Proceedings of the International Conference on New Diamond Science and Technology, 403 (1991); P.A. Dennig, D.A. Stevenson, Proceedings of the First International Conference on the Applications of Diamond Films and Related Materials, 383 (1991).].