Apparatus for use in drilling

Claim 2

A drill element of the kind specified in which the screw thread has a root and a crest which are interconnected through a main flank, an effective diameter selected from the range 25 millimeters to 65 millimeters and a pitch angle α and in which, in a section of the screw thread taken on the longitudinal axis thereof, the main flank is flat or substantially flat and is inclined at a flank angle β to a plane which is normal to the longitudinal axis and wherein α is determined, or substantially so, from the formula ##EQU8## where TU is the uncoupling torque, TC is the coupling torque, TU/TC is in the range 0.36 to 0.46; β is in the range of 30° to 65°, and α as determined is not greater than 9.5°.

Claim 3

A drill element as claimed in claim 1 in which β is in the range 30° to 60°.

Claim 4

A drill element as claimed in claim 2 in which β is in the range 50° to 60° and α as determined is not less than 6.5°.

Claim 5

A drill element as claimed in claim 2 in which β is in the range 30° to 54° and with β in the range 50° to 54° α as determined is not greater than 6.5°.

Claim 6

A drill element as claimed in claim 4 in which β is in the range 40° to 50°, TU/TC is 0.39 and the pitch angle α is as determined from the formula with a tolerance in the range ±0.3°.

Claim 7

A drill element as claimed in claim 1 and having a flank angle β of substantially 45° and a pitch angle α of substantially 6.5°.

Claim 8

A drill element as claimed in claim 1 in which the extent or height measured radially over which the main flank is intended to abut an opposing complementary main flank in a male/female coupling of two of the drill elements lies within the range H∓ 10%, h being determined from the formula h=8.06×10.sup.-6 φ.sup.3 -2.8×10.sup.-3 φ.sup.2 +0.27φ-5.07 wherein φ is the effective diameter in millimeters.

Claim 9

A drill element as claimed in claim 1 in which the crest and root are flat, or substantially flat, in a section of the screw thread taken on the longitudinal axis thereof whereby said crest and root respectively lie in the surfaces of notional cylinders which are concentric with the thread axis.

Claim 10

A drill element as claimed in claim 1 in which the crest extends between the main flank and a secondary flank, said secondary flank being flat, or substantially flat, in a section of the screw thread taken on the longitudinal axis thereof and being inclined at a flank angle γ to a plane which is normal to the longitudinal axis of the screw thread so that the main flank and secondary flank converge towards each other as they approach the crest which communicates between said flanks, and wherein the flank angle γ is in the range of 30° to 65°.

Claim 11

A drill element as claimed in claim 9 in which transition regions are provided on the screw thread between the secondary flank and the adjacent crest and between the secondary flank and the adjacent root, said transition regions being of a chamfered or fair curved profile which alleviates the formation of an abrupt change in direction of the thread surface.

Claim 12

A drill element as claimed in claim 1 wherein the flank angle γ is substantially the same as the flank angle β.

Claim 13

A drill element as claimed in claim 11 in which the pitch of the thread form is substantially symmetrical in the axial direction of the screw thread about the mid-axial width position of the crest.

Claim 14

A drill element as claimed in claim 1 in which transition regions are provided on the screw thread between the main flank and the adjacent crest and between the main flank and the adjacent root, said transition regions being of a chamfered or fair curved profile which alleviates the formation of an abrupt change in direction of the thread surface.

Claim 15

A drill element as claimed in claim 13 in which the transition regions are radiussed to provide convex surfaces between the crest and adjacent flanks and concave surfaces between the root and adjacent flanks.

Claim 16

A drill element as claimed in claim 14 in which the radii of the transition regions is selected from the range 1.5 millimeters to 3.5 millimeters.

Claim 17

The combination of two drill elements each of which is as claimed in claim 1, a first of said drill elements having its screw thread internal and the second drill element having its screw thread external, said screw threads being complementary and engageable, or in engagement, with each other so that the main flank of one drill element opposes and is capable of, or is in, substantially face-to-face and sliding abutment with the main flank of the other drill element.

Claim 18

The combination of two drill elements as claimed in claim 16 in which the thread forms of the two drill elements are substantially the same and for each thread form the crest extends between the main flank and a secondary flank, said secondary flank being flat, or substantially flat, in a section of the screw thread taken on the longitudinal axis thereof and being inclined at a flank angle γ to a plane which is normal to the longitudinal axis of the screw thread so that the main flank and secondary flank converge towards each other as they approach the crest which communicates between said flanks, and the flank angle γ is in the range of 30° to 65°, and wherein the opposing secondary flanks are in axially spaced relationship when the opposing main flanks are in abutment to provide an endfloat which measured in the axial direction is in the range 0.5 millimeters to 0.9 millimeters.

Claim 19

A drill element as claimed in claim 10 in which the transition regions are radiussed to provide convex surfaces between the crest and adjacent flanks and concave surfaces between the root and adjacent flanks.

Claim 20

A drill element as claimed in claim 18 in which the radii of the transition regions is selected from the range 1.5 millimeters to 3.5 millimeters.