The pin on disc (POD) tests revealed an inverse relationship between coefficient of friction and the particle size of boric acid. So, as the properties of materials are changing with respect to its spatial dimension, the tribological performance of solid lubricant in the metal cutting is a matter of research. The present work aims at investigating the effect of variation of particle size of boric acid in the nano level in the machining of hardened steel. Canola oil and SAE 40 oil are tested as the carrying media for nano crystalline boric acid. In both cases, all the machining parameters viz. cutting forces, tool temperatures and surface roughness increased with the decrease of the particle size in nano level. The effect of carrying medium is also targeted and SAE 40 oil has been found as the best.