EARTH BORING CUTTER EMPLOYING HELICAL TEETH

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to cutters for earth bits.

2. Description of the Related Art

An earth bit is commonly used to bore holes into a formation. Such holes may be bored for many different reasons, such as drilling for oil, minerals and geothermal steam. There are several different types of earth bits that are used to bore holes. One type is a rotary earth bit and, in a typical setup, it includes three earth bit cutting cones rotatably mounted to a corresponding lug. The lugs are mounted on an earth bit body and, as the earth bit body is rotated in the bore hole, the earth bit cutting cones rotate in response to contacting the formation.

Another type of earth bit is a rolling cutter earth bit which typically includes a number of saddles carried by an earth bit body. A cutter is coupled with the earth bit body by rotatably mounting it to a saddle. Each cutter includes a number of teeth for boring into the formation. Examples of rolling cutter earth bits are disclosed in U.S. Pat. Nos. 3,444,939, 4,040,493, 4,161,225, 4,167,980, 4,393,949 and 5,456,328.

Most of these rolling cutter earth bits include cutters which are designed to bore through hard or medium hard formations, instead of soft formations such as soft limestone and soft-to-medium shale. Further, most of these rolling cutter earth bits include cutters which generate smaller cuttings. These rolling cutter earth bits typically include cutters which experience a significant amount of tracking, wherein the teeth of one cutter will follow in the path of the teeth of another cutter. It is desirable to reduce the amount of tracking because tracking reduces the operating life of the cutters and undesirably reduces the drilling efficiency of the earth bit.

Hence, there is a need for a rolling cutter earth bit for boring through soft formations, wherein the rolling cutter earth bit includes cutters which experience less tracking. Further, there is a need for a rolling cutter earth bit which includes cutters that generate larger cuttings when boring through soft formations.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a cutter, which includes a cutter body having opposed openings, and a plurality of curved teeth extending around the outer periphery, and between opposed ends, of the cutter body. The curved teeth have a curved edge, and a curved leading face that curves as it extends between opposed ends of the cutter body.

The cutter can include many other features. For example, in some embodiments, the curved teeth are positioned so that one end of a curved tooth overlaps the opposed end of an adjacent curved tooth.

In some embodiments, the opposed ends of each curved tooth have different dimensions from each other. In some embodiments, the curved teeth include a curved leading face that curves as it extends between opposed ends of the cutter body. The plurality of curved teeth can include at least one curved tooth having first and second tooth portions spaced apart from each other. In some embodiments, the plurality of curved teeth includes first and second notched curved teeth. The notches of the first and second notched curved teeth can be offset from each other. In some embodiments, the plurality of curved teeth includes an unnotched curved tooth.

The invention provides an earth bit, which includes an earth bit body and a first cutter rotatably mounted to the earth bit body with a first saddle. The first cutter includes a cutter body, and a first plurality of curved teeth extending in a direction around the outer periphery, and between opposed ends, of the cutter body. The curved teeth are positioned so that one end of a curved tooth overlaps an opposed end of an adjacent curved tooth.

The earth bit can include many other features. For example, in some embodiments, the dimensions of a curved tooth at its end surface are smaller than the dimensions of the curved tooth at its opposed end surface. The curved teeth can include a curved edge and a curved face that curves as it extends away from the curved edge. In some embodiments, the first plurality of curved teeth includes at least one curved tooth having first and second tooth portions spaced apart from each other.

In one embodiment, the earth bit further includes a second cutter rotatably mounted to the earth bit body with a second saddle. The second cutter includes a cutter body and a second plurality of curved teeth extending between opposed ends and in an opposed direction around the outer periphery of the cutter body. The curved teeth of the second cutter are positioned so that one end of a curved tooth overlaps the opposed end of an adjacent curved tooth. In some embodiments, the number of curved teeth of the first and second cutters are the same. The first and second saddles can be offset from each other.

In some embodiments, the earth bit further includes a third cutter rotatably mounted to the earth bit body with a third saddle. The third cutter includes a cutter body and a third plurality of curved teeth extending between opposed ends and in the direction around the outer periphery of the cutter body. The curved teeth of the third cutter are positioned so that one end of a curved tooth overlaps the opposed end of an adjacent curved tooth. In this embodiment, the second cutter is positioned between the first and third cutters.

The invention provides an earth bit, which includes an earth bit body, and a lug and cutting cone carried by the earth bit body, wherein the cutting cone is rotatably mounted to the lug. The earth bit includes a plurality of cutters carried by the earth bit body, wherein the cutters include a cutter body and a plurality of curved teeth extending between opposed ends of the cutter body. The curved teeth are positioned so that one end of a tooth overlaps an opposed end of an adjacent tooth. The curved teeth of a first cutter extend in a direction around its corresponding cutter body and the curved teeth of a second cutter extend in an opposed direction around its corresponding cutter body.

The earth bit can include many other features. For example, in some embodiments, a tooth of the first cutter includes first and second tooth portions spaced apart from each other. In some embodiments, the dimensions of a curved tooth of the first cutter at its opposed end surfaces are different.

In some embodiments, the earth bit includes a third cutter having teeth which extend in the same direction as the teeth of the first cutter, wherein the second cutter is positioned between the first and third cutters. In these embodiments, the second cutter is offset from the first and third cutters to reduce the amount of tracking experienced by the teeth of the cutters.

Further features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1
a, 1b and 1c are perspective, side and end views, respectively, of a cutter having a frusto-conical cutter body and straight teeth.

FIG. 2
a is a perspective view of a cutter, in accordance with the invention, having unnotched curved teeth.

FIGS. 2
b and 2c are opposed end views of the cutter of FIG. 2a.

FIG. 2
d is a close-up end view of the cutter of FIG. 2a.

FIGS. 3
a and 3b are perspective and side views, respectively, of a cutter, in accordance with the invention, having notched curved teeth.

FIGS. 3
c and 3d are opposed end views of the cutter of FIG. 3a.

FIGS. 3
e and 3f are close-up end and side views, respectively, of the cutter of FIG. 3a.

FIGS. 4
a and 4b are perspective and side views, respectively, of a cutter, in accordance with the invention, having notched curved teeth.

FIGS. 4
c and 4d are opposed end views of the cutter of FIG. 4a.

FIGS. 4
e and 4f are close-up end and side views, respectively, of the cutter of FIG. 4a.

FIGS. 5
a and 5b are bottom perspective and bottom views, respectively, of an embodiment of a rolling cutter earth bit, in accordance with the invention.

FIGS. 6
a and 6b are bottom perspective and bottom views, respectively, of another embodiment of a rolling cutter earth bit, in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a cutter, and an earth bit which employs the cutter, for boring through soft formations. The cutter, in accordance with the invention, includes teeth that generate large cuttings when boring through the soft formations. Further, the earth bit, in accordance with the invention, includes a plurality of such cutters positioned to reduce the amount of tracking experienced by the teeth of the cutters. The operating life of the cutters and the drilling efficiency of the earth bit both increase in response to reducing the amount of tracking experienced by the teeth. It should be noted that the cutters disclosed herein can be interchanged with other types of cutters, such as those used to bore through hard and medium hard formations (i.e. formations that are harder than soft limestone and soft-to-medium shale). Hence, the cutters of the earth bit are interchangeable so that the earth bit can be modified to improve its ability to bore through soft, medium hard and hard formations.

FIG. 1
a is a perspective view of a cutter 100 having a frusto-conical cutter body 101 and a straight tooth 103, and FIGS. 1b and 1c are side and end views, respectively, of cutter 100. In this embodiment, cutter 100 includes a central opening 102 which extends through cutter body 101 and between opposed ends 106a and 106b. Cutter body 101 has a smaller outer diameter at end 106a than at end 106b. In this way, cutter body 101 has a frusto-conical shape.

In this embodiment, central opening 102 has the same shape and dimension at ends 106a and 106b and is sized and shaped to receive a shaft (not shown), so that cutter 100 can be rotatably mounted to an earth bit. Cutter 100 can be rotatably mounted to the earth bit in many different ways. In some embodiments, the earth bit includes a saddle and shaft, and cutter 100 is rotatably mounted to the saddle by extending the shaft through central opening 102. The shaft extends through opposed ends of central opening 102. More information regarding earth bits is provided with FIGS. 5a and 5b and FIGS. 6a and 6b.

In this embodiment, straight tooth 103 extends along the outer periphery of cutter body 101 and between opposed ends 106a and 106b. In general, cutter 100 can include any number of straight teeth, but it includes thirteen straight teeth here for illustrative purposes. In some embodiments, the number of teeth of cutter 100 is in a range between about seven and nineteen because this number of teeth has been found to be useful when boring through soft formations, such as soft limestone and soft-to-medium shale. Further, this number of teeth is useful to generate cuttings of a desired size when boring through soft formations. Hence, the size of the cuttings can be controlled by controlling the number of teeth included with cutter 100.

In this embodiment, straight tooth 103 includes a flat face 104 and straight edge 105, wherein flat face 104 and straight edge 105 do not curve between ends 106a and 106b. In this way, tooth 103 is a straight tooth with a flat face. The flatness and straightness of flat face 104 and straight edge 105 can best be seen in the side and end views of FIGS. 1b and 1c, respectively. It should be noted that the length of straight tooth 103 typically corresponds with the length of straight edge 105. Hence, the length of straight tooth 103 increases and decreases as the length of straight edge 105 increases and decreases, respectively.

In this embodiment, straight tooth 103 includes opposed surfaces 116a (FIG. 1a) and 116b (FIG. 1b) positioned proximate to ends 106a and 106b, respectively. Flat face 104 and straight edge 105 do not curve between surfaces 116a and 116b. In this way, tooth 103 is a straight tooth with a flat face. In cutter 100, surfaces 116a and 116b have the same shape and dimensions, wherein the shape is triangular. The dimensions of surfaces 116a and 116b can be characterized in many different ways. In this embodiment, surfaces 116a and 116b have the same dimensions because they have the same areas. In particular, surface 116a has the same area as surface 116b.

In FIG. 1c, a radial line 109 extends radially and outwardly from a center 108 of cutter body 101. Straight edge 105 extends between opposed ends 106a and 106b so that it is perpendicular to radial line 109. Further, straight edge 105 extends between opposed surfaces 116a and 116b so that it is perpendicular to radial line 109. Radial line 109 extends so that it bisects opposed surfaces 116a and 116b of straight tooth 103. Radial line 109 bisects surface 116a because the shape and area of surface 116a is the same on opposed sides of radial line 109. Further, radial line 109 bisects surface 116b because the shape and area of surface 116b is the same on opposed sides of radial line 109. Straight edge 105 bisects surfaces 116a and 116b because it is perpendicular to radial line 109, and tooth 103 is a straight tooth.

It should be noted that radial line 109 can be positioned, without changing its angle relative to cutter body 101 and center 108, at any location of cutter body 101 between surfaces 116a and 116b and intersect straight edge 105. For example, radial line 109 is shown as being proximate to surfaces 116a and 116b in FIG. 1a, wherein it intersects straight edge 105 proximate to surfaces 116a and 116b. In this way, radial line 109 can intersect straight edge 105 at any position between surfaces 116a and 116b without changing its angle relative to cutter body 101 and center 108. Hence, the same radial line (i.e. radial lines oriented at the same angle) extends through the intersection of straight edge 105 with opposed surfaces 116a and 116b.

FIG. 2
a is a perspective view of a cutter 110, in accordance with the invention, and FIGS. 2b and 2c are opposed end views of cutter 110. Cutter 110 is similar to cutter 100 discussed above, and includes cutter body 101 with central opening 102. However, in accordance with the invention, cutter 110 includes an unnotched curved tooth 113 which extends in a direction 107a between opposed ends 106a and 106b and along the outer periphery of cutter body 101. Direction 107a is in a clockwise direction when looking towards end 106a (FIG. 2b) and direction 107a is in a counterclockwise direction when looking towards end 106b (FIG. 2c). Cutter 110 can include any number of unnotched curved teeth, but it includes thirteen unnotched curved teeth here for illustrative purposes. In some embodiments, the number of unnotched curved teeth of cutter 110 is in a range between about seven and nineteen for reasons mentioned above.

In this embodiment, unnotched curved tooth 113 includes a curved face 114 and curved edge 115, wherein curved face 114 and curved edge 115 curve between ends 106a and 106b. Further, curved face 114 curves as it extends away from curved edge 115. In this way, curved tooth 113 is a curved tooth with a curved face. Hence, curved tooth 113 is not a straight tooth with a flat face, like tooth 103 discussed above. The curvature of curved face 114 and curved edge 115 can be seen in FIGS. 2a, 2b and 2c. It should be noted that curved face 114 is a curved leading face because it engages the formation in response to the rotation of cutter 110 in direction 107a.

In this embodiment, unnotched curved tooth 113 includes opposed surfaces 116a (FIG. 2b) and 116b (FIG. 2c) positioned proximate to ends 106a and 106b, respectively. Curved face 114 and curved edge 115 curve between surfaces 116a and 116b. In this way, tooth 113 is a curved tooth with a curved face. In cutter 110, surfaces 116a and 116b can have many different shapes, such as triangular. However, the shapes of surfaces 116a and 116b of cutter 110 are typically different from each other. For example, in one embodiment, surface 116a is shaped like an equilateral triangle and surface 116b is not shaped like an equilateral triangle. In another embodiment, surface 116a is shaped like an isosceles triangle and surface 116b is not shaped like an isosceles triangle. In one embodiment, surface 116a is shaped like an equilateral triangle and surface 116b is shaped like an isosceles or scalene triangle. In another embodiment, surface 116a is shaped like an isosceles triangle and surface 116b is shaped like an equilateral or scalene triangle. In this way, the shapes of surfaces 116a and 116b of cutter 110 are different from each other. It should be noted that, in FIGS. 2b and 2c, surfaces 116a and 116b are shaped like isosceles and scalene triangles, respectively.

The dimensions of surfaces 116a and 116b of cutter 110 are typically different from each other. As mentioned above, the dimensions of surfaces 116a and 116b can be characterized in many different ways. In this embodiment, surfaces 116a and 116b have different dimensions because they have different areas. In particular, surfaces 116a and 116b have different dimensions because surface 116a has a smaller area than surface 116b.

In FIG. 2b and 2c, radial lines 109a and 109b extend radially and outwardly from center 108 of cutter body 101, wherein radial lines 109a and 109b are proximate to ends 106a and 106b, respectively. Radial line 109a extends so that it intersects the intersection of curved edge 115 and surface 116a, and radial line 109b extends so that it intersects the intersection of curved edge 115 and surface 116b. Radial line 109a extends so that it bisects surface 116a (FIG. 2b) because the shape and area of surface 116a of tooth 113 is the same on opposed sides of radial line 109a. Radial line 109a bisects surface 116a when surface 116a has a shape like an equilateral or isosceles triangle. Radial line 109b extends so that it does not bisect surface 116b (FIG. 2c) because the shape and area of surface 116b of tooth 113 is not the same on opposed sides of radial line 109b. Radial line 109b extends so that it does not bisect surface 116b when the shape of surface 116b is not an equilateral or isosceles triangle. Radial line 109b extends so that it does not bisect surface 116b when the shape of surface 116b is a scalene triangle. Hence, surface 116a is symmetrical with radial line 109a and surface 116b is non-symmetrical with radial line 109b.

In this embodiment, curved edge 115 curves between radial lines 109a and 109b. Curved edge 115 is curved so that radial lines 109a and 109b are at an angle θ₁relative to each other, as seen in FIGS. 2b and 2c. Angle θ₁is nonzero so that the same radial line does not extend through the intersections of curved edge 115 and opposed surfaces 116a and 116b, as with cutter 100.

Angle θ₁can have many different angular values. For example, in one embodiment, angle θ₁is less than about twenty degrees and, in another embodiment, angle θ₁is less than about fifteen degrees. In one particular embodiment, angle θ₁is between about two degrees and fifteen degrees. In another particular embodiment, angle θ₁is between about five degrees and twenty degrees.

In general, the amount of curvature of tooth 113 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. The amount of curvature of curved face 114 and curved edge 115 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. Further, the amount of twist of tooth 113 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. As the amount of twist of tooth 113 increases and decreases, the amount of twist of curved face 114 and curved edge 115 increases and decreases, respectively. In this way, the amount of curvature and twist of tooth 113 is adjustable in response to adjusting the magnitude of angle θ₁.

In general, the length of unnotched curved tooth 113 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. The length of unnotched curved tooth 113 typically corresponds with the length of curved edge 115. The length of unnotched curved tooth 113 increases and decreases as the length of curved edge 115 increases and decreases, respectively. Hence, the length of curved edge 115 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively.

It should be noted that the curvature of unnotched curved tooth 113, for a constant angle θ₁, typically increases and decreases as the length of curved edge 115 decreases and increases, respectively. Further, the curvature of unnotched curved tooth 113, for a constant length of curved edge 115, typically increases and decreases as angle θ₁increases and decreases, respectively.

FIG. 2
d is a close-up end view of cutter 110 looking towards end 106a, as in FIG. 2b. In accordance with the invention, the unnotched curved teeth of cutter 110 overlap each other. The unnotched curved teeth of cutter 110 can overlap each other in many different ways. As shown in FIG. 2d, cutter 110 includes unnotched curved teeth 113a and 113b, which are adjacent to each other. Curved teeth 113a and 113b are the same as curved tooth 113 discussed above. Curved tooth 113a includes curved face 114a and curved edge 115a, and curved tooth 113b includes curved face 114b and curved edge 115b. Radial line 109a extends between center 108 of cutter body 101 and the intersection of surface 116a of tooth 113a and curved edge 115a. Further, radial line 109b extends between center 108 of cutter body 101 and the intersection of surface 116b of curved tooth 113a and curved edge 115a. A radial line 109c extends between center 108 of cutter body 101 and the intersection of surface 116a of tooth 113b and curved edge 115b. As mentioned above, radial lines 109a and 109b are at angle θ₁relative to each other. Further, radial lines 109a and 109c are at an angle θ₂relative to each other. It should be noted that radial lines 109a and 109c are proximate to end 106a, and radial line 109b is proximate to end 106b.

In accordance with the invention, curved teeth 113a and 113b overlap each other. The overlapping of curved teeth 113a and 113b can be characterized in many different ways. In this embodiment, curved teeth 113a and 113b overlap each other because angle θ₁is greater than angle θ₂. Angle θ₁is greater than angle θ₂so that a curved edge portion 117b of curved edge 115b overlaps a curved edge portion 117a of curved edge 115a. Curved edge portions 117a and 117b extend between radial lines 109b and 109c. Hence, curved teeth 113a and 113b overlap each other because curved edge portions of curved edges 115a and 115b overlap each other. In this way, cutter 110 includes unnotched curved teeth which overlap each other.

Angle θ₁is greater than angle θ₂so that a curved surface portion 118b of curved surface 114b overlaps a curved surface portion 118a of curved surface 114a. Curved surface portions 118a and 118b extend between radial lines 109b and 109c. Curved surface portion 118a is bounded between radial lines 109b and 109c and curved edge portion 117a and surface 116b of tooth 113a. Further, curved surface portion 118b is bounded between radial lines 109b and 109c and curved edge portion 117b and surface 116a of tooth 113b. Hence, curved teeth 113a and 113b overlap each other because curved surface portions of curved surfaces 114a and 114b overlap each other. In this way, cutter 110 includes unnotched curved teeth which overlap each other.

The amount of overlap of curved teeth 113a and 113b can be adjusted in many different ways. For example, the difference between angles θ₁and θ₂can be increased by increasing the curvature of curved surface 114a. Further, the difference between angles θ₁and θ₂can be increased by increasing the curvature of curved edge 115a. The difference between angles θ₁and θ₂can be decreased by decreasing the curvature of curved surface 114a. Further, the difference between angles θ₁and θ₂can be decreased by decreasing the curvature of curved edge 115a. In this way, the amount of overlap of curved teeth 113a and 113b can be adjusted in response to adjusting the curvature of curved surface 114a and curved edge 115a.

It should be noted that curved teeth 113a and 113b do not overlap each other when angle θ₁is less than angle θ₂. Further, curved teeth 113a and 113b do not substantially overlap each other when angles θ₁and θ₂are substantially the same. In some embodiments, cutter 110 provides an improved cutting efficiency when teeth 113a and 113b do not overlap each other, and when curved teeth 113a and 113b do not substantially overlap each other. For example, in some embodiments, cutter 110 provides an improved cutting efficiency when angle θ₁is between zero degrees and five degrees less than angle θ₂. In some embodiments, cutter 110 provides an improved cutting efficiency when angle θ₁is between zero degrees and ten degrees less than angle θ₂. In some embodiments, cutter 110 provides an improved cutting efficiency when angle θ₁is between zero degrees and fifteen degrees less than angle θ₂.

In the embodiment of FIG. 2d, curved teeth 113a and 113b overlap each other so that the intersection of curved edge 115a and surface 116b of curved tooth 113a leads the intersection of curved edge 115b and surface 116a of curved tooth 113b in response to rotating cutter body 101 in direction 107a. In this way, the intersection of curved edge 115a and surface 116b of curved tooth 113a impacts the formation before the intersection of curved edge 115b and surface 116a of curved tooth 113b in response to rotating cutter body 101 in direction 107a. Further, curved edge portion 117a impacts the formation before curved edge portion 117b, and curved surface portion 118a impacts the formation before curved surface portion 118b.

Cutter 110 provides many advantages. For example, the curved teeth of cutter 110 overlap each other so that cutter 110 is more stable in response to cutter body 101 rotating in direction 107a. Cutter 110 is more stable in response to cutter body 101 rotating in direction 107a because at least one curved tooth of cutter 110 will always be in contact with the formation. In this way, the curved teeth will hold cutter body 101 to the formation so that it vibrates less. Further, the curved teeth of cutter 110 will remain in contact with the formation for a longer amount of time than a straight tooth, such as tooth 103. The curved teeth of cutter 110 will remain in contact with the formation for a longer amount of time than a straight tooth because a curved tooth is generally longer than a straight tooth. Also, a curved tooth is longer than a straight tooth so that its number of impacts per revolution of cutter body 101 is reduced. For example, a single curved tooth will experience one impact per revolution, but a straight tooth may experience multiple impacts per revolution.

Another advantage provided by cutter 110 is that the curved teeth are not torqued upwardly in response to engaging the formation. It is known that straight teeth will be lifted up in response to engaging the formation, which causes them to experience an upwardly directed force that torques them. It is undesirable to torque the teeth of a cutter in this manner because they can fracture and become detached from cutter body 101.

Another advantage provided by cutter 110 is that curved teeth 113 each have a wider base which is blended into cutter body 101 for additional strength. The base of a curved tooth also facilitates the removal of cuttings from between adjacent curved teeth and reduces the likelihood of pack-off. A cutting is a portion of the formation that has been cut by the cutter. Pack-off occurs when a portion of the cutting is cut from the formation and becomes lodged between adjacent teeth. Pack-off will result in an effectively shortened tooth which will reduce the penetration rate of the tooth into the formation.

FIG. 3
a is a perspective view of a cutter 120, in accordance with the invention, and FIGS. 3b and 3c are end and side views, respectively, of cutter 120. Cutter 120 is similar to cutter 110 discussed above, and includes cutter body 101 with central opening 102. However, in accordance with the invention, cutter 120 includes a notched curved tooth 123 which extends in direction 107a between opposed ends 106a and 106b and along the outer periphery of cutter body 101. Cutter 120 can include any number of notched curved teeth, but it includes thirteen notched curved teeth here for reasons discussed above. In some embodiments, the number of notched curved teeth of cutter 120 is in a range between about seven and nineteen. It should be noted that all the teeth included with cutter 120 can be notched curved teeth, or one or more of the teeth included with cutter 120 can be notched curved teeth. In this embodiment, cutter 120 includes one tooth (i.e. tooth 113) that is unnotched, and several curved teeth that are notched.

In accordance with the invention, notched curved tooth 123 includes first and second tooth portions 126 and 127 with a notch 128 positioned between them. In this way, first and second tooth portions 126 and 127 are spaced apart from each other by notch 128. Hence, tooth 123 is a notched tooth and is not an unnotched tooth like teeth 103 and 113 discussed above. Teeth 103 and 113 are unnotched teeth because they do not include first and second tooth portions spaced apart from each other with a notch. It should be noted that first and second tooth portions 126 and 127, as well as notch 128, extend around cutter body 101 in the same direction as notched curved tooth 123. Hence, first and second tooth portions 126 and 127 and notch 128 extend in direction 107a because notched curved tooth 123 extends in direction 107a.

In this embodiment, notched curved tooth 123 includes curved face 114 and curved edge 115 (FIG. 3b), wherein curved face 114 and curved edge 115 curve between ends 106a and 106b. In this way, notched curved tooth 123 is a curved tooth with a curved face. Hence, notched curved tooth 123 is not a straight tooth with a flat face like tooth 103 discussed above. The curvature of curved face 114 and curved edge 115 can be seen in FIGS. 3a, 3b and 3c. It should be noted that curved face 114 and curved edge 115 extend through first and second tooth portions 126 and 127. Hence, tooth portions 126 and 127 both include portions of curved face 114 and curved edge 115.

In this embodiment, unnotched curved tooth 123 includes opposed surfaces 116a (FIG. 3c) and 116b (FIG. 3d) positioned proximate to ends 106a and 106b, respectively. Curved face 114 and curved edge 115 curve between surfaces 116a and 116b. In this way, tooth 123 is a curved tooth with a curved face. In cutter 120, surfaces 116a and 116b can have many different shapes, such as triangular. However, the shapes of surfaces 116a and 116b of cutter 120 are typically different from each other. For example, in one embodiment, surface 116a is shaped like an equilateral triangle and surface 116b is not shaped like an equilateral triangle. In another embodiment, surface 116a is shaped like an isosceles triangle and surface 116b is not shaped like an isosceles triangle. In one embodiment, surface 116a is shaped like an equilateral triangle and surface 116b is shaped like an isosceles or scalene triangle. In another embodiment, surface 116a is shaped like an isosceles triangle and surface 116b is shaped like an equilateral or scalene triangle. In this way, the shapes of surfaces 116a and 116b of cutter 120 are different from each other. It should be noted that, in FIGS. 3c and 3d, surfaces 116a and 116b are shaped like isosceles and scalene triangles, respectively.

The dimensions of surfaces 116a and 116b of cutter 120 are typically different from each other. As mentioned above, the dimensions of surfaces 116a and 116b can be characterized in many different ways. In this embodiment, surfaces 116a and 116b have different dimensions because they have different areas. In particular, surface 116a has a smaller area than surface 116b.

It should be noted that surfaces 116a and 116b are included with first and second tooth portions 126 and 127, respectively. As shown in FIGS. 3a, 3c and 3d, first tooth portion 126 includes a surface 116c which is opposed to surface 116a, and second tooth portion 127 includes a surface 116d which is opposed to surface 116b. Hence, first tooth portion 126 extends between surfaces 116a and 116c and second tooth portion 127 extends between surfaces 116b and 116d. Further, notch 128 extends between surfaces 116c and 116d. Curved face 114 and curved edge 115 of first tooth portion 126 extend between surfaces 116a and 116c, and curved face 114 and curved edge 115 of second tooth portion 127 extend between surfaces 116b and 116d.

It should be noted that, in this embodiment, surfaces 116c and 116d have different dimensions. The dimensions of surfaces 116c and 116d can be characterized in many different ways, such as those discussed above with surfaces 116a and 116b. In this embodiment, surfaces 116c and 116d have different dimensions because they have different areas. In particular, surface 116c has a smaller area than surface 116d. In other embodiments, surfaces 116c and 116d have the same dimensions wherein surfaces 116c and 116d have the same areas.

It should also be noted that, in this embodiment, surfaces 116c and 116d can have the same or different shapes. The shapes of surfaces 116c and 116d can be characterized in many different ways, such as those discussed above with surfaces 116a and 116b. In this embodiment, surfaces 116c and 116d have the same shape because they are both isosceles triangles. In other embodiments, surfaces 116c and 116d have the same shape because they are both equilateral or scalene triangles. In other embodiments, surfaces 116c and 116d have different shapes. For example, in one embodiment, surfaces 116c and 116d are shaped like equilateral and isosceles triangles, respectively.

In FIGS. 3c and 3d, radial lines 109a and 109b extend radially and outwardly from center 108 of cutter body 101, wherein radial lines 109a and 109b are proximate to ends 106a and 106b, respectively. Radial line 109a extends so that it intersects the intersection of curved edge 115 and surface 116a, and radial line 109b extends so that it intersects the intersection of curved edge 115 and surface 116b. Radial line 109a extends so that it bisects surface 116a (FIG. 3c) because the shape and area of surface 116a of tooth 123 is the same on opposed sides of radial line 109a. Radial line 109b extends so that it does not bisect surface 116b (FIG. 3d) because the shape and area of surface 116b of tooth 123 is not the same on opposed sides of radial line 109b. Hence, surface 116a is symmetrical with radial line 109a and surface 116b is non-symmetrical with radial line 109b.

In this embodiment, curved edge 115 (FIG. 3b) of tooth portions 126 and 127 curves between radial lines 109a and 109b. Curved edge 115 is curved so that radial lines 109a and 109b are at an angle θ₁relative to each other, as seen in FIGS. 3c and 3d. Angle θ₁is nonzero so that the same radial line does not extend through the intersections of curved edge 115 and opposed surfaces 116a and 116b, as with cutter 100.

Angle θ₁can have many different angular values, such as those mentioned in more detail above with cutter 110. In general, the amount of curvature of tooth 123 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. The amount of curvature of curved face 114 and curved edge 115 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. Further, the amount of twist of tooth 123 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. As the amount of twist of tooth 123 increases and decreases, the amount of twist of curved face 114 and curved edge 115 increases and decreases, respectively. In this way, the amount of curvature and twist of tooth 123 is adjustable in response to adjusting the magnitude of angle θ₁.

The amount of curvature of first and second tooth portions 126 and 127 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. The amount of curvature of curved face 114 and curved edge 115 of first and second tooth portions 126 and 127 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. Further, the amount of twist of first and second tooth portions 126 and 127 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. As the amount of twist of first and second tooth portions 126 and 127 increase and decrease, the amount of twist of curved face 114 and curved edge 115 increases and decreases, respectively. In this way, the amount of curvature and twist of first and second tooth portions 126 and 127 is adjustable in response to adjusting the magnitude of angle θ₁.

In general, the length of notched curved tooth 123 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. The length of notched curved tooth 123 typically corresponds with the length of curved edge 115. The length of notched curved tooth 123 increases and decreases as the length of curved edge 115 increases and decreases, respectively. Hence, the length of curved edge 115 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively.

It should be noted that the curvature of notched curved tooth 123, for a constant angle θ₁, typically increases and decreases as the length of curved edge 115 decreases and increases, respectively. Further, the curvature of notched curved tooth 123, for a constant length of curved edge 115, typically increases and decreases as angle θ₁increases and decreases, respectively.

FIG. 3
e is a close-up end view of cutter 120 looking towards end 106a, as in FIG. 3b. In accordance with the invention, the curved teeth of cutter 120 overlap each other. It should be noted that the notched and unnotched curved teeth of cutter 120 generally overlap each other. The curved teeth of cutter 120 can overlap each other in many different ways. As shown in FIG. 3e, cutter 120 includes notched curved teeth 123a, 123b and 123c, which are adjacent to each other. Notched curved tooth 123b is positioned between notched curved teeth 123a and 123c. Curved teeth 123a, 123b and 123c are the same as curved tooth 123 discussed above.

Curved tooth 123a includes first and second tooth portions 126a and 127a with a curved face 114a and curved edge 115a. Curved face 114a and curved edge 115a extend through tooth portions 126a and 127a. Curved tooth 123b includes first and second tooth portions 126b and 127b with a curved face 114b and curved edge 115b. Curved face 114b and curved edge 115b extend through tooth portions 126b and 127b. Curved tooth 123c includes first and second tooth portions 126c and 127c with a curved face 114c and curved edge 115c. Curved face 114c and curved edge 115c extend through tooth portions 126c and 127c.

Radial line 109a extends between center 108 of cutter body 101 and the intersection of surface 116a of tooth 123b and curved edge 115b. Further, radial line 109b extends between center 108 of cutter body 101 and the intersection of surface 116b of curved tooth 123b and curved edge 115b. A radial line 109c extends between center 108 of cutter body 101 and the intersection of surface 116a of tooth 123c and curved edge 115c. As mentioned above, radial lines 109a and 109b are at angle θ₁relative to each other. Further, radial lines 109a and 109c are at an angle θ₂relative to each other. It should be noted that radial lines 109a and 109c are proximate to end 106a, and radial line 109b is proximate to end 106b.

In accordance with the invention, notched curved teeth 123b and 123c overlap each other. The overlapping of notched curved teeth 123b and 123c can be characterized in many different ways. In this embodiment, curved teeth 123b and 123c overlap each other because angle θ₁is greater than angle θ₂. Angle θ₁is greater than angle θ₂so that a curved edge portion 117c of curved edge 115c overlaps curved edge portion 117b of curved edge 115b. Curved edge portions 117b and 117c extend between radial lines 109b and 109c. Hence, curved teeth 123b and 123c overlap each other because curved edge portions of curved edges 115b and 115c overlap each other. In this way, cutter 120 includes unnotched curved teeth which overlap each other.

Angle θ₁is greater than angle θ₂so that a curved surface portion 118c of curved surface 114c overlaps curved surface portion 118b of curved surface 114b. Curved surface portions 118b and 118c extend between radial lines 109b and 109c. Curved surface portion 118b is bounded between radial lines 109b and 109c and curved edge portion 117b and surface 116b of tooth 123b. Further, curved surface portion 118c is bounded between radial lines 109b and 109c and curved edge portion 117c and surface 116c of tooth 113c. Hence, curved teeth 123b and 123c overlap each other because curved surface portions of curved surfaces 114b and 114c overlap each other. In this way, cutter 120 includes notched curved teeth which overlap each other.

The amount of overlap of curved teeth 123b and 123c can be adjusted in many different ways. For example, the difference between angles θ₁and θ₂can be increased by increasing the curvature of curved surface 114b of tooth portion 127b. Further, the difference between angles θ₁and θ₂can be increased by increasing the curvature of curved edge 115b of tooth portion 127b. The difference between angles θ₁and θ₂can be decreased by decreasing the curvature of curved surface 114b of tooth portion 127b. Further, the difference between angles θ₁and θ₂can be decreased by decreasing the curvature of curved edge 115b of tooth portion 127b. In this way, the amount of overlap of curved teeth 123b and 123c can be adjusted in response to adjusting the curvature of curved surface 114b and curved edge 115b of tooth portion 127b.

It should be noted that curved teeth 123b and 123c do not overlap each other when angle θ₁is less than angle θ₂. Further, curved teeth 123b and 123c do not substantially overlap each other when angles θ₁and θ₂are substantially the same. In some embodiments, cutter 120 provides an improved cutting efficiency when teeth 123a and 123b do not overlap each other, and when curved teeth 123a and 123b do not substantially overlap each other. For example, in some embodiments, cutter 120 provides an improved cutting efficiency when angle θ₁is between zero degrees and five degrees less than angle θ₂. In some embodiments, cutter 120 provides an improved cutting efficiency when angle θ₁is between zero degrees and ten degrees less than angle θ₂. In some embodiments, cutter 120 provides an improved cutting efficiency when angle θ₁is between zero degrees and fifteen degrees less than angle θ₂.

In the embodiment of FIG. 3e, curved teeth 123b and 123c overlap each other so that the intersection of curved edge 115b and surface 116b of curved tooth 123b leads the intersection of curved edge 115c and surface 116a of curved tooth 123c in response to rotating cutter body 101 in direction 107a. In this way, the intersection of curved edge 115b and surface 116b of curved tooth 123b impacts the formation before the intersection of curved edge 115c and surface 116a of curved tooth 123c in response to rotating cutter body 101 in direction 107a.

FIG. 3
f is a close-up side view of cutter 120, as seen in FIG. 3b. In accordance with the invention, the notches of each adjacent notched curved tooth are offset from each other. The notches of each adjacent notched curved tooth can be offset from each other in many different ways. For example, the notches of each adjacent curved tooth can be staggered relative to each other. When the notches of adjacent curved teeth are staggered relative to each other, they are a different distance away from end 106a. Further, when the notches of adjacent curved teeth are staggered relative to each other, they are a different distance from end 106b.

For example, in this embodiment, cutter 120 includes notched curved teeth 123a, 123b and 123c, wherein notched curved tooth 123c is positioned between notched curved teeth 123a and 123b. Notched curved teeth 123a, 123b and 123c include notches 128a, 128b and 128c, respectively. Notches 128a, 128b and 128c are positioned distances D₁, D₂and D₃, respectively, from end 106b, wherein distance D₁is less than distance D₂and distance D₂is less than distance D₃. In this way, notches 128a, 128b and 128c are different distances from end 106b so that they are staggered relative to each other.

It should be noted that distances D₁, D₂and D₃can correspond to many different distances between end 106b and corresponding notches 128a, 128b and 128c. For example, in this embodiment, distance D₁is the distance between end 106b and the intersection of surface 116d and curved edge 115a of tooth portion 127a of tooth 123a. Distance D₂is the distance between end 106b and the intersection of surface 116d and curved edge 115b of tooth portion 127b of tooth 123b. Further, distance D₃is the distance between end 106b and the intersection of surface 116d and curved edge 115c of tooth portion 127c of tooth 123c. It should be noted that three different notch positions for the staggered notches are shown in this example for illustrative purposes. However, cutter 120 generally includes two or more different notch positions for the staggered notches.

Cutter 120 provides many advantages, such as those mentioned above with cutter 110. For example, the curved teeth of cutter 120 overlap each other so that cutter 120 is more stable in response to cutter body 101 rotating in direction 107a. Another advantage provided by cutter 120 is that the notches allow material from the cuttings to flow therethrough, which reduces the likelihood of pack-off and increases the drilling efficiency. In general, the drilling efficiency increases when cutter 120 cuts through more material per rotation. Further, the notches are staggered relative to each other, which facilitates the removal of material from between adjacent teeth and reduces the amount of pack-off.

FIG. 4
a is a perspective view of a cutter 130, in accordance with the invention, and FIGS. 4b and 4c are end and side views, respectively, of cutter 130. Cutter 130 is similar to cutters 110 and 120 discussed above, and includes cutter body 101 with central opening 102. However, in accordance with the invention, cutter 130 includes a notched curved tooth 133 which extends in a direction 107b between opposed ends 106a and 106b and along the outer periphery of cutter body 101. Direction 107b is opposed to direction 107a. Hence, direction 107b is clockwise if direction 107a is counterclockwise, and direction 107b is counterclockwise if direction 107a is clockwise.

Cutter 130 can include any number of notched curved teeth, but it includes thirteen notched curved teeth here for reasons discussed above. In some embodiments, the number of notched curved teeth of cutter 130 is in a range between about seven and nineteen. It should be noted that all the teeth included with cutter 130 can be notched curved teeth, or one or more of the teeth included with cutter 130 can be notched curved teeth. In this embodiment, cutter 130 includes one tooth (i.e. tooth 113) that is unnotched, and several curved teeth that are notched.

In accordance with the invention, notched curved tooth 133 includes first and second tooth portions 136 and 137 with a notch 138 positioned between them. In this way, first and second tooth portions 136 and 137 are spaced apart from each other by notch 138. Hence, tooth 133 is a notched tooth and is not an unnotched tooth like teeth 103 and 113 discussed above. Teeth 103 and 113 are unnotched teeth because they do not include first and second tooth portions spaced apart from each other with a notch. It should be noted that first and second tooth portions 136 and 137, as well as notch 138, extend around cutter body 101 in the same direction as notched curved tooth 133. Hence, first and second tooth portions 136 and 137 and notch 138 extend in direction 107b because notched curved tooth 133 extends in direction 107b.

In this embodiment, notched curved tooth 133 includes curved face 114 and curved edge 115 (FIG. 4b), wherein curved face 114 and curved edge 115 curve between ends 106a and 106b. In this way, notched curved tooth 133 is a curved tooth with a curved face. Hence, notched curved tooth 133 is not a straight tooth with a flat face, like tooth 103 discussed above. The curvature of curved face 114 and curved edge 115 can be seen in FIGS. 4a, 4b and 4c. It should be noted that curved face 114 and curved edge 115 extend through first and second tooth portions 136 and 137. Hence, tooth portions 136 and 137 both include portions of curved face 114 and curved edge 115.

In this embodiment, unnotched curved tooth 133 includes opposed surfaces 116a (FIG. 4c) and 116b (FIG. 4d) positioned proximate to ends 106a and 106b, respectively. Curved face 114 and curved edge 115 curve between surfaces 116a and 116b. In this way, tooth 133 is a curved tooth with a curved face. In cutter 130, surfaces 116a and 116b can have many different shapes, such as triangular. However, the shapes of surfaces 116a and 116b of cutter 130 are typically different from each other. For example, in one embodiment, surface 116a is shaped like an equilateral triangle and surface 116b is not shaped like an equilateral triangle. In another embodiment, surface 116a is shaped like an isosceles triangle and surface 116b is not shaped like an isosceles triangle. In one embodiment, surface 116a is shaped like an equilateral triangle and surface 116b is shaped like an isosceles or scalene triangle. In another embodiment, surface 116a is shaped like an isosceles triangle and surface 116b is shaped like an equilateral or scalene triangle. In this way, the shapes of surfaces 116a and 116b of cutter 130 are different from each other. It should be noted that, in FIGS. 4c and 4d, surfaces 116a and 116b are shaped like isosceles and scalene triangles, respectively.

The dimensions of surfaces 116a and 116b of cutter 130 are typically different from each other. As mentioned above, the dimensions of surfaces 116a and 116b can be characterized in many different ways. In this embodiment, surfaces 116a and 116b have different dimensions because they have different areas. In particular, surface 116a has a smaller area than surface 116b.

It should be noted that surfaces 116a and 116b are included with first and second tooth portions 136 and 137, respectively. As shown in FIGS. 4a, 4c and 4d, first tooth portion 146 includes surface 116c which is opposed to surface 116a, and second tooth portion 137 includes surface 116d which is opposed to surface 116b. Hence, first tooth portion 136 extends between surfaces 116a and 116c and second tooth portion 137 extends between surfaces 116b and 116d. Further, notch 138 extends between surfaces 116c and 116d. Curved face 114 and curved edge 115 of first tooth portion 136 extend between surfaces 116a and 116c, and curved face 114 and curved edge 115 of second tooth portion 137 extend between surfaces 116b and 116d.

In FIGS. 4c and 4d, radial lines 109a and 109b extend radially and outwardly from center 108 of cutter body 101, wherein radial lines 109a and 109b are proximate to ends 106a and 106b, respectively. Radial line 109a extends so that it intersects the intersection of curved edge 115 and surface 116a, and radial line 109b extends so that it intersects the intersection of curved edge 115 and surface 116b. Radial line 109a extends so that it bisects surface 116a (FIG. 4c) because the shape and area of surface 116a of tooth 123 is the same on opposed sides of radial line 109a. Radial line 109b extends so that it does not bisect surface 116b (FIG. 4d) because the shape and area of surface 116b of tooth 123 is not the same on opposed sides of radial line 109b. Hence, surface 116a is symmetrical with radial line 109a and surface 116b is non-symmetrical with radial line 109b.

In this embodiment, curved edge 115 (FIG. 4b) of tooth portions 136 and 137 curves between radial lines 109a and 109b. Curved edge 115 is curved so that radial lines 109a and 109b are at an angle θ₁relative to each other, as seen in FIGS. 4c and 4d. Angle θ₁is nonzero so that the same radial line does not extend through the intersections of curved edge 115 and opposed surfaces 116a and 116b, as with cutter 100. Angle θ₁can have many different angular values. In general, the amount of curvature of tooth 133 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. The amount of curvature of curved face 114 and curved edge 115 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. Further, the amount of twist of tooth 133 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. As the amount of twist of tooth 133 increases and decreases, the amount of twist of curved face 114 and curved edge 115 increases and decreases, respectively. In this way, the amount of curvature and twist of tooth 133 is adjustable in response to adjusting the magnitude of angle θ₁.

The amount of curvature of first and second tooth portions 136 and 137 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. The amount of curvature of curved face 114 and curved edge 115 of first and second tooth portions 136 and 137 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. Further, the amount of twist of first and second tooth portions 136 and 137 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. As the amount of twist of first and second tooth portions 136 and 137 increase and decrease, the amount of twist of curved face 114 and curved edge 115 increases and decreases, respectively. In this way, the amount of curvature and twist of first and second tooth portions 136 and 137 is adjustable in response to adjusting the magnitude of angle θ₁.

In general, the length of notched curved tooth 133 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively. The length of notched curved tooth 133 typically corresponds with the length of curved edge 115. The length of notched curved tooth 133 increases and decreases as the length of curved edge 115 increases and decreases, respectively. Hence, the length of curved edge 115 increases and decreases as the magnitude of angle θ₁increases and decreases, respectively.

It should be noted that the curvature of notched curved tooth 133, for a constant angle θ₁, typically increases and decreases as the length of curved edge 115 decreases and increases, respectively. Further, the curvature of notched curved tooth 133, for a constant length of curved edge 115, typically increases and decreases as angle θ₁increases and decreases, respectively.

FIG. 4
e is a close-up end view of cutter 130 looking towards end 106a, as in FIG. 4b. In accordance with the invention, the curved teeth of cutter 130 overlap each other. It should be noted that the notched and unnotched curved teeth of cutter 130 generally overlap each other. The curved teeth of cutter 130 can overlap each other in many different ways. As shown in FIG. 4e, cutter 130 includes notched curved teeth 133a and 133b which are adjacent to each other. Curved teeth 133a and 133b are the same as curved tooth 133 discussed above.

Curved tooth 133a includes first and second tooth portions 136a and 137a with curved face 114a and curved edge 115a. Curved face 114a and curved edge 115a extend through tooth portions 136a and 137a. Curved tooth 133b includes first and second tooth portions 136b and 137b with curved face 114b and curved edge 115b. Curved face 114b and curved edge 115b extend through tooth portions 136b and 137b.

Radial line 109a extends between center 108 of cutter body 101 and the intersection of surface 116a of tooth 133a and curved edge 115a. Further, radial line 109b extends between center 108 of cutter body 101 and the intersection of surface 116b of curved tooth 133a and curved edge 115a. Radial line 109c extends between center 108 of cutter body 101 and the intersection of surface 116a of tooth 133b and curved edge 115b. As mentioned above, radial lines 109a and 109b are at angle θ₁relative to each other, and radial lines 109a and 109c are at an angle θ₂relative to each other. It should be noted that radial lines 109a and 109c are proximate to end 106a, and radial line 109b is proximate to end 106b.

In accordance with the invention, notched curved teeth 133a and 133b overlap each other. The overlapping of notched curved teeth 133a and 133b can be characterized in many different ways. In this embodiment, curved teeth 133a and 133b overlap each other because angle θ₁is greater than angle θ₂. Angle θ₁is greater than angle θ₂so that a curved edge portion 117b of curved edge 115b overlaps a curved edge portion 117a of curved edge 115a. Curved edge portions 117a and 117b extend between radial lines 109b and 109c. Hence, curved teeth 133a and 133b overlap each other because curved edge portions of curved edges 115a and 115b overlap each other. In this way, cutter 130 includes unnotched curved teeth which overlap each other.

Angle θ₁is greater than angle θ₂so that curved surface portion 118b of curved surface 114b overlaps curved surface portion 118a of curved surface 114a. Curved surface portions 118a and 118b extend between radial lines 109b and 109c. Curved surface portion 118a is bounded between radial lines 109b and 109c and curved edge portion 117a and surface 116b of tooth 133a. Further, curved surface portion 118b is bounded between radial lines 109b and 109c and curved edge portion 117b and surface 116a of tooth 113b. Hence, curved teeth 133a and 133b overlap each other because curved surface portions of curved surfaces 114a and 114b overlap each other. In this way, cutter 130 includes notched curved teeth which overlap each other.

The amount of overlap of curved teeth 133a and 133b can be adjusted in many different ways. For example, the difference between angles θ₁and θ₂can be increased by increasing the curvature of curved surface 114a of tooth portion 137a. Further, the difference between angles θ₁and θ₂can be increased by increasing the curvature of curved edge 115a of tooth portion 137a. The difference between angles θ₁and θ₂can be decreased by decreasing the curvature of curved surface 114a of tooth portion 137a. Further, the difference between angles θ₁and θ₂can be decreased by decreasing the curvature of curved edge 115a of tooth portion 137a. In this way, the amount of overlap of curved teeth 133a and 133b can be adjusted in response to adjusting the curvature of curved surface 114a and curved edge 115a of tooth portion 137a.

It should be noted that curved teeth 133a and 133b do not overlap each other when angle θ₁is less than angle θ₂. Further, curved teeth 133a and 133b do not substantially overlap each other when angles θ₁and θ₂are substantially the same. In some embodiments, cutter 130 provides an improved cutting efficiency when teeth 133a and 133b do not overlap each other, and when curved teeth 133a and 133b do not substantially overlap each other. For example, in some embodiments, cutter 130 provides an improved cutting efficiency when angle θ₁is between zero degrees and five degrees less than angle θ₂. In some embodiments, cutter 130 provides an improved cutting efficiency when angle θ₁is between zero degrees and ten degrees less than angle θ₂. In some embodiments, cutter 130 provides an improved cutting efficiency when angle θ₁is between zero degrees and fifteen degrees less than angle θ₂.

In the embodiment of FIG. 4e, curved teeth 133a and 133b overlap each other so that the intersection of curved edge 115a and surface 116b of curved tooth 133a leads the intersection of curved edge 115b and surface 116a of curved tooth 133b in response to rotating cutter body 101 in direction 107b. In this way, the intersection of curved edge 115a and surface 116b of curved tooth 133a impacts the formation before the intersection of curved edge 115b and surface 116a of curved tooth 133b in response to rotating cutter body 101 in direction 107b.

FIG. 4
f is a close-up side view of cutter 130, as seen in FIG. 4b. In accordance with the invention, the notches of each adjacent notched curved tooth are offset from each other. The notches of each adjacent notched curved tooth can be offset from each other in many different ways. For example, the notches of each adjacent curved tooth can be staggered relative to each other. When the notches of adjacent curved teeth are staggered relative to each other, they are a different distance away from end 106a. Further, when the notches of adjacent curved teeth are staggered relative to each other, they are a different distance from end 106b.

For example, in this embodiment, cutter 130 includes notched curved teeth 133a, 133b and 133c, wherein notched curved tooth 133c is positioned between notched curved teeth 133a and 133b. Notched curved teeth 133a, 133b and 133c include notches 138a, 138b and 138c, respectively. Notches 138a, 138b and 138c are positioned distances D₁, D₂and D₃, respectively, from end 106b, wherein distance D₁is less than distance D₂and distance D₂is less than distance D₃. In this way, notches 138a, 138b and 138c are different distances from end 106b so that they are staggered relative to each other.

It should be noted that distances D₁, D₂and D₃can correspond to many different distances between end 106b and corresponding notches 138a, 138b and 138c. For example, in this embodiment, distance D₁is the distance between end 106b and the intersection of surface 116d and curved edge 115a of tooth portion 137a of tooth 133a. Distance D₂is the distance between end 106b and the intersection of surface 116d and curved edge 115b of tooth portion 137b of tooth 133b. Further, distance D₃is the distance between end 106b and the intersection of surface 116d and curved edge 115c of tooth portion 137c of tooth 133c. It should be noted that three different notch positions for the staggered notches are shown in this example for illustrative purposes. However, cutter 130 generally includes two or more different notch positions for the staggered notches.

Cutter 130 provides many advantages, such as those mentioned above with cutters 110 and 120. For example, the curved teeth of cutter 130 overlap each other so that cutter 130 is more stable in response to cutter body 101 rotating in direction 107a. Another advantage provided by cutter 130 is that the notches allow material from the cuttings to flow therethrough, which reduces the likelihood of pack-off and increases the drilling efficiency. Further, the notches are staggered relative to each other, which facilitates the removal of material from between adjacent teeth and reduces the amount of pack-off. Another advantage provided by cutter 120 is that the notches allow material from the cuttings to flow therethrough, which reduces the likelihood of pack-off

FIGS. 5
a and 5b are bottom perspective and bottom views, respectively, of an earth bit 150, in accordance with the invention, which can carry the cutters discussed above. In this embodiment, earth bit 150 is embodied as a rolling cutter earth bit and includes an earth bit body 151 which carries saddles 152, 153, 154, 155 and 156. Earth bit 150 includes cutters 120 and 130, wherein cutter 120 is rotatably mounted to saddles 153 and 156 and cutter 130 is rotatably mounted to saddles 152, 154 and 155. Cutters 120 and 130 are discussed in more detail above. Saddles 152, 153, 154, 155 and 156 are positioned so that their longitudinal axis extends radially outwardly from a center 158 (FIG. 5b) of earth bit body 151. The longitudinal axis of saddle 152 is indicated in FIGS. 5a and 5b and denoted as axis 169, wherein axis 169 extends through center 158. It should be noted that the cutter rotatably mounted to saddle 152 rotates about axis 169.

The amount of tracking experienced by the cutters of an earth bit is typically reduced by including cutters having different numbers of teeth. However, in accordance with the invention, the cutters of earth bit 150 experience less tracking, even when they have the same number of teeth. The cutters of earth bit 150 can experience less tracking even when they have the same number of teeth in many different ways.

In accordance with the invention, the saddles of earth bit 150 are positioned relative to each other to reduce the amount of tracking experienced by the teeth of the cutters of earth bit 150. The saddles of earth bit 150 can be positioned relative to each other in many different ways to reduce the amount of tracking experienced by the teeth of the cutters of earth bit 150. As best seen in FIG. 5b, the saddles are offset so that they are positioned at various distances from center 158 of earth bit body 151.

For example, in this embodiment, saddles 153 and 155 are positioned closer to center 158 than saddles 152, 154 and 156 so that the cutters rotatably mounted to saddles 153 and 155 are closer to center 158 than the cutters rotatably mounted to saddles 152, 154 and 156. In particular, saddles 153 and 155 are positioned a radial distance from center 158, wherein the radial distance corresponds with the radius of a reference circle 157. Further, saddles 152, 154 and 156 are positioned a radial distance from center 158, wherein the radial distance corresponds with the radius of a reference circle 159. The radius of reference circle 157 is less than the radius of reference circle 159 so that saddles 153 and 155 are closer to center 158 than saddles 152, 154 and 156. In this way, saddles 153 and 155 are positioned closer to center 158 than saddles 152, 154 and 156. The radius of reference circle 157 is less than the radius of reference circle 159 so that the cutters rotatably mounted to saddles 153 and 155 are closer to center 158 than the cutters rotatably mounted to saddles 152, 154 and 156. In this way, the cutters rotatably mounted to saddles 153 and 155 are positioned closer to center 158 than the cutters rotatably mounted to saddles 152, 154 and 156.

In accordance with the invention, the types of cutters rotatably mounted in the saddles of earth bit 150 are selected to reduce the amount of tracking experienced by their teeth. The types of cutters rotatably mounted in the saddles of earth bit 150 can be selected in many different ways to reduce the amount of tracking experienced by their teeth. In this embodiment, saddle 153 is positioned between saddles 152 and 154. As mentioned above, cutter 130 is rotatably mounted with saddles 152 and 154, and cutter 120 is rotatably mounted with saddle 153. In this way, cutter 120 is positioned between two cutters 130. Cutter 120 includes teeth that curve in direction 107a and cutter 130 includes teeth that curve in direction 107b. Hence, the amount of tracking experienced by the teeth of the cutters rotatably mounted to saddles 152, 153 and 154 is reduced by positioning a cutter with teeth curving in one direction (i.e. direction 107a) between two cutters with teeth curving in an opposed direction (i.e. direction 107b). It should be noted that the amount of tracking experienced by the two cutters is reduced even when they both include the same or a different number of teeth.

In some embodiments, cutter 130 is rotatably mounted to saddle 153 and cutter 130 is rotatably mounted to saddles 152 and 154. In this way, the amount of tracking experienced by the teeth of the cutters rotatably mounted to saddles 152, 153 and 154 is reduced by positioning a cutter with teeth curving in one direction (i.e. direction 107b) between two cutters with teeth curving in an opposed direction (i.e. direction 107a).

Hence, in accordance with the invention, cutters 120 and 130 of earth bit 150 can each have the same number of teeth and still experience less tracking. In this particular embodiment, cutters 120 and 130 of earth bit 150 each have thirteen teeth. However, as mentioned above, cutters 120 and 130 can each include a number of teeth within a range of about seven to nineteen, wherein the number of teeth of cutters 120 and 130 are the same. Hence, cutter 120 includes eleven teeth if cutter 130 includes eleven teeth and cutter 120 includes fourteen teeth if cutter 130 includes fourteen teeth.

It should be noted that the cutters of earth bit 150 are interchangeable and replaceable with the cutters discussed herein. Hence, any of cutters 100, 110, 120 and 130 can be rotatably mounted to saddles 152, 153, 154, 155 and 156. The selection of which cutters are included with earth bit 150 depends on many different factors, such as the hardness of the formation it is desired to bore through. For example, cutter 100 and/or cutter 110 are typically selected when it is desired to bore through a hard or medium hard formation. Further, cutter 120 and/or cutter 130 are typically selected when it is desired to bore through a soft formation. In this way, the cutters of earth bit 100 are interchangeable and can be chosen in response to the type of formation it is desired to bore through.

FIGS. 6
a and 6b are bottom perspective and bottom views, respectively, of an earth bit 160, in accordance with the invention, which can carry the cutters discussed above. In this embodiment, earth bit 160 is embodied as a rolling cutter earth bit and includes earth bit body 151 which carries saddles 152, 153, 154, 155 and 156, which are discussed above. Earth bit 160 includes cutters 120 and 130, wherein cutter 120 is rotatably mounted to saddles 153 and 156 and cutter 130 is rotatably mounted to saddles 152, 154 and 155. Cutters 120 and 130 are discussed in more detail above. Saddles 152, 153, 154, 155 and 156 are positioned so that their longitudinal axis extends radially outwardly from center 158 (FIG. 6b) of earth bit body 151. The longitudinal axis of saddle 152 is indicated in FIGS. 6a and 6b and denoted as axis 169, wherein axis 169 extends through center 158. It should be noted that the cutter rotatably mounted to saddle 152 rotates about axis 169.

As mentioned above, the amount of tracking experienced by the cutters of an earth bit is typically reduced by including cutters having different numbers of teeth. However, in accordance with the invention, the cutters of earth bit 160 experience less tracking, even when they have the same number of teeth. The cutters of earth bit 160 can experience less tracking even when they have the same number of teeth in many different ways, such as those discussed above with earth bit 150.

In accordance with the invention, the saddles of earth bit 160 are positioned relative to each other to reduce the amount of tracking experienced by the teeth of the cutters of earth bit 150. The saddles of earth bit 160 can be positioned relative to each other in many different ways to reduce the amount of tracking experienced by the teeth of the cutters of earth bit 160. As best seen in FIG. 6b, the saddles are offset so that they are positioned at various distances from center 158 of earth bit body 151. More information about offsetting saddles of an earth bit is provided above with FIGS. 5a and 5b.

In this embodiment, the amount of tracking experienced by the teeth of the cutters of earth bit 100 is reduced by includes a cutting cone 161 rotatably mounted to a lug 162, wherein lug 162 is carried by earth bit body 151. Lug 162 and cutting cone 161 are positioned between saddles 152 and 156, wherein cutters 130 and 120 are rotatably mounted to saddles 152 and 156, respectively. In this way, lug 162 and cutting cone 161 are positioned between cutters 120 and 130. It should be noted that, in some embodiments, cutters 120 and 130 are rotatably mounted with saddles 152 and 156, respectively.

While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.

EARTH BORING CUTTER EMPLOYING HELICAL TEETH

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