To drill the flat-bottomed hole for the cup, you'll need a 35-millimeter Forstner bit. Mark a depth line ½ inch up the side of the bit, position it on the center point, and bore into the door until you hit the line

Install The Hinge Cups
https://www.thisoldhouse.com/cabinets/21016567/how-to-instal...


WHAT IS A HINGE CUP?
Hinge CupA hinge cup refers to a recession that is required for setting certain styles of invisible hinges. Hinge cup, cup hinge, Euro Hinge and invisible hinge are all terms that are commonly used interchangeably despite a few subtle differences. A hinge cup is one part of the invisible hinge that, along with the arm, makes up the movable half of a door mechanism. The complimentary piece to a hinge cup is called a mounting plate.

When setting the hinge cup, it is important to decide if the cabinet door is to have a profiled edge. If so then be sure that the router bit does not cut into the cups circumference. The hole drilled to set the hinge cup should be a flat-bottom hole drilled into the back of the cabinet door, and it is equally important to be certain that this drilling will not break through to the beveled edge of the door. The location and the depth of the hole will have some variance from brand to brand, but the diameter is generally 35mm.
https://kitchencabinetkings.com/glossary/hinge-cup/