The present invention provides a grinding cup having a lower grinding cup having a lower grinding section (32) connected to form a grinding cup having top and bottom surfaces. The grinding section is formed from a material capable of grinding the hard materials such as tungsten carbide inserts of button bits etc. A centrally disposed convex recess is formed in the bottom surface having the desired size and profile for the button to be found. Drive means are provided on or in the upper body section that cooperate with the output shaft of the grinding machine. The drive means and the upper body section or grinding section of the grinding cup are adapted to optimize the engagement surfaces and points of contact between the grinding cup and rotor or adapter to reduce negative impact on operational stability and rotor wear, as well as other potential associated wear to the grinding apparatus caused by vibration and/or resonance.
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