Hollow crown drill with end face cutting members

A hollow crown drill comprising an axially extending annular carrier member (1) having a rotational direction (D) and a leading cutting end face, at least one set of cutting members comprising at least two cutting members (2, 3, 4, 6, 7, 8, 9), said cutting members in each said set of cutting members having an exposed cutting face (2a, 3a, 4a, 6a, 7a, 8a, 9a) of a different size having a radially extending width and an axially extending height and facing in the rotational direction (D), and the cutting members (2, 3, 4, 6, 7, 8, 9) in one set of cutting members increase in size counter to the rotational direction (D), wherein the improvement comprises that the radially extending width (b) of said cutting faces (2a, 3a, 4a, 6a, 7a, 8a, 9a) of the cutting members in one set of cutting members is calculated based on the equation:

• ##EQU2## wherein the symbols in the equation represent the following:
• bi--radially extending width of one of said cutting faces (2a, 3a, 4a, 6a, 7a, 8a, 9a),
• i--the specific one (1 to N) of the said cutting members (2, 3, 4, 6, 7, 8, 9) in one said set of cutting members increasing counter to the rotational direction (D),
• b--width of the cutting face (4a, 7a, 9a) of the last cutting member of one set of cutting members located counter to the rotational direction (D),
• N--total number of cutting members (2, 3, 4, 6, 7, 8, 9) in said one set of cutting members, and
• k--0.7 to 1.5.