FIG. 1 is a top plan view of a first embodiment of my ornamental design for a grinding disc;
FIG. 2 is a side view of the first embodiment;
FIG. 3 is another side view of the first embodiment;
FIG. 4 is another side view of the first embodiment;
FIG. 5 is another side view of the first embodiment;
FIG. 6 is a bottom plan view of the first embodiment;
FIG. 7 is a top, front perspective view of the first embodiment;
FIG. 8 is a top plan view of a second embodiment of my ornamental design for a grinding disc;
FIG. 9 is a side view of the second embodiment;
FIG. 10 is another side view of the second embodiment;
FIG. 11 is another side view of the second embodiment;
FIG. 12 is another side view of the second embodiment;
FIG. 13 is a bottom plan view of the second embodiment;
FIG. 14 is a top, front perspective view of the second embodiment;
FIG. 15 is a top plan view of a third embodiment of my ornamental design for a grinding disc;
FIG. 16 is a side view of the third embodiment;
FIG. 17 is another side view of the third embodiment;
FIG. 18 is another side view of the third embodiment;
FIG. 19 is another side view of the third embodiment;
FIG. 20 is a bottom plan view of the third embodiment;
FIG. 21 is a top, front perspective view of the third embodiment;
FIG. 22 is a top plan view of a fourth embodiment of my ornamental design for a grinding disc;
FIG. 23 is a side view of the fourth embodiment;
FIG. 24 is another side view of the fourth embodiment;
FIG. 25 is another side view of the fourth embodiment;
FIG. 26 is another side view of the fourth embodiment;
FIG. 27 is a bottom plan view of the fourth embodiment;
FIG. 28 is a top, front perspective view of the fourth embodiment;
FIG. 29 is a top plan view of a fifth embodiment of my ornamental design for a grinding disc;
FIG. 30 is a side view of the fifth embodiment;
FIG. 31 is another side view of the fifth embodiment;
FIG. 32 is another side view of the fifth embodiment;
FIG. 33 is another side view of the fifth embodiment;
FIG. 34 is a bottom plan view of the fifth embodiment;
FIG. 35 is a top, front perspective view of the fifth embodiment;
FIG. 36 is a top plan view of a sixth embodiment of my ornamental design for a grinding disc;
FIG. 37 is a side view of the sixth embodiment;
FIG. 38 is another side view of the sixth embodiment;
FIG. 39 is another side view of the sixth embodiment;
FIG. 40 is another side view of the sixth embodiment;
FIG. 41 is a bottom plan view of the sixth embodiment; and,
FIG. 42 is a top, front perspective view of the sixth embodiment.