High Pressure Grinding Rolls - HPGR is a relatively new technology first implemented in Europe into Cement Industry and later incorporated into Mineral industry in the late 20th century as replacement to conventional mills like rod and ball mills due to the higher efficiencies offered by them in comminuting the material fed to the mill. These are heavy duty machines designed to operate for 60–100 thousand hours, hence making millions of revolutions in their lifetime at the operating speed of 14–17 RPM sustaining thousands of Kilo-Newtons of force. As a result these machines are very expensive and bulky which makes their failure and other serious damages a very expensive affair. Hence, it is necessary to make sure they are designed and operated properly so as to avoid serious breakdowns without compromising. One such HPGR was found to be failing at half of its designed lifetime. This paper covers the detailed Finite Element Simulation done on Ansys Workbench 2019 R2 which is validated through numerical calculations of shaft design under combined and fluctuating load according to ASME code standards. The design shortcomings are found out and minimum strength required for the roll and shaft assembly is proposed. © 2021