The present invention relates to a locking device and particularly but not exclusively to a locking device for preventing relative rotation between two parts.

BACKGROUND TO THE INVENTION

There are many situations where it is desired to prevent a nut from rotating on a bolt, and a number of ways of achieving this are known. Thread-locking fluid such as LOCTITE (RTM) is available in a variety of strengths and may be used to prevent nuts from working loose from their bolts due to vibration, for example. However, such thread-locking fluid is only suitable for use on smaller sizes of nuts and bolts.

A known method of locking a larger sized nut onto a bolt involves drilling through the nut and bolt, at right angles to the bolt, when the nut is in its desired position. A pin, such as a split pin or a slotted sprung pin, can then be passed through the hole, so that the nut is prevented from rotating on the bolt.

In some situations, nuts may need to be tightened from time-to-time, for example to take up a gap between parts which have become worn. This will involve rotating the nut, so that the hole in the nut is no longer aligned with the hole in the bolt. A further hole will therefore have to be drilled. This is time-consuming, especially if regular adjustment is required. Drilling a further hole will also weaken the bolt, and a bolt with more than one hole drilled through may be unacceptable in some situations.

In order to couple a rotating machine element to a shaft, a key may be used. A key- seat is provided in the shaft, a key-way is provided in the rotating element, and a rigid key is inserted to prevent relative rotation between the shaft and the machine element, allowing torque to be transmitted from one to the other.

Key-seats and key-ways often need to be milled into custom one-off parts, and take considerable time to machine. It can be particularly problematic to refurbish key- seats where damage has occurred. It is an object of the invention to provide an improved locking device and a further object of the invention to provide an improved keyed connector.

STATEMENT OF INVENTION

According to a first aspect of the invention, there is provided a locking element for rotationally locking a component to a shaft, comprising a first portion having a planar base for resting on a planar surface provided across a chord of a circular shaft, and a second portion having at least one bearing surface, the second portion forming a key for engaging in and bearing against a keyway cut in the component.

The first portion of the key fits within a void defined by the circular shaft and an annular component surrounding the shaft, the annular component having an interior diameter similar to the diameter of the shaft.

The locking element may be used to engage a shaft with a rotating component, for example a cog. To install the locking element, a flat surface needs to be milled all the way across a part of the shaft. This operation is substantially less time-consuming than milling a conventional key-seat in the shaft. The large flat bearing surface of the horizontal cylindrical segment of the locking element also results in lower stress than on a traditional rectangular profile key.

A tang may be provided on the locking element, extending from the flat surface of the horizontal cylindrical segment. The tang is provided where the locking element is for use at an end of a shaft, and prevents the locking element from slipping off the end of the shaft. The tang may extend from one side of the locking element to the other, parallel to the chord defining the horizontal cylindrical segment. A slot will need to be milled in the shaft to correspond with the tang, but this is a simple operation as the slot extends across the entire width of the milled flat surface of the shaft.

The planar base may have a substantially central longitudinal cut-out. The longitudinal cut-out ensures that, in use, the planar base of the locking element abuts a milled surface of a shaft at either side, and not in the centre. Where a shaft has a longitudinal hole drilled through it, the centre of the milled surface may be thin, and relatively weak. The centre of the milled surface may also deform slightly, if for example an oversize screw is driven into the hole in the shaft. Preferably, the cut-out is a V-shaped groove, and extends from one end of the planar base of the locking element to the other.

The locking element may include two curved faces, each curved face having two curves in opposing directions. For example, each curved face may have a main curve defining a convex surface, and a secondary curve in the opposite direction to the main curve, interrupting the main curve and forming a concave indent in the convex surface. The shape thus formed, substantially S-shaped in profile on each side of the locking element, allows the locking element to be used with shafts of various different diameters, with minimal removal of material, and yet still provides a strong and robust locking element. Excess material may be ground away. Advantageously, the ability of a single locking element to be used with a number of shaft diameters allows a smaller inventory of parts to be carried by machine shops.

According to a second aspect of the present invention, there is provided a locking pin for locking a female threaded component to a male threaded component, preventing relative rotation, the locking pin having an elongate pin body and at least one cutting edge.

A locking pin with a sharp cutting edge may be inserted into a hole in a nut or similar, to cut through the thread of a corresponding threaded member, for example a bolt. By cutting through the thread with a sharp cutting edge, burring and other damage to the thread is minimised, so that once the pin is removed, the thread will still function correctly, and the nut can be unscrewed.

A locking pin may equally be passed through a hole in the head of a bolt or other male threaded member, to cut through the thread of a corresponding nut or other female threaded member.

The locking pin may be in the form of a cylindrical tube having a longitudinal slot along its entire length, and may be made from a sprung material. This allows the pin to fit resiliently and tightly. Different sizes of locking pin may be provided for different applications.

Where the locking pin is cylindrical, a longitudinal slot may or may not be provided, and, where provided, the longitudinal slot may be along the entire length of the pin, or may be along only a portion of the length of the pin.

The cutting edge may have a lead portion for assisting in positioning the locking pin in an aperture.

A cutting tooth may extend from the pin body substantially along its elongate extent, and the extent of the cutting tooth from the pin body may be lesser at at least one end than it is in the centre. A tapered cutting tooth allows the end of the locking pin to be easily introduced into a hole next to a thread. Force may then be applied, for example with a hammer, so that the cutting tooth of the pin cuts through the thread.

The extent of the cutting tooth from the pin body may be lesser at each end than it is in the centre. Providing a tooth which is tapered at both ends allows the pin to be inserted either way around.

The locking pin may be curved perpendicular to its elongate extent, having a convex face and a concave face, the cutting tooth or teeth extending from the concave face. Such a curved locking pin may be introduced into a cut-out in, for example, a nut, the cut-out extending through the thread of the nut around a portion of the circumference of the thread.

A portion of screw thread may be provided on the locking pin body. Where the pin body is curved as described above, the screw thread portion may be provided on the convex face. The screw thread portion allows a retaining screw to be inserted into, for example, a nut, adjacent to the hole or cut-out into which the locking pin is inserted. The retaining screw holds the locking pin into the hole or cut-out. Alternatively, a portion of the locking pin may be made from an elastically deformable material, for example nylon. This allows a retaining screw to cut into part of the locking pin, again holding the locking pin in place. The retaining screw may be removed when the locking pin needs to be removed. Once the retaining screw has been removed, the locking pin may be pulled out with, for example, pliers. Alternatively, where the hole in the nut for the retaining screw is an untapped hole, the locking pin may be removed by continuing to screw the retaining screw into the blind hole. When the retaining screw reaches the base of the hole, continued turning of the thread will act to draw the locking pin out from the nut.

A threaded hole may be provided in the pin body, parallel to the elongate extent of the pin. The threaded hole may either be a blind hole or a through hole. Where a threaded hole is provided, the locking pin may be driven entirely into a hole or cutout, leaving no protruding portion. Removal of the locking pin may be effected by driving a screw partially into the threaded hole in the pin body. The screw may then be gripped with, for example, pliers, and the locking pin pulled out.

Where the threaded hole in the pin body is a through hole, and the hole or cut-out for the locking pin in the nut is a blind hole, the locking pin may be removed by driving a screw into the threaded hole in the locking pin, and continuing to drive the screw when it hits the base of the blind hole in the nut. As the screw is driven against the base of the hole in the nut, the locking pin is drawn out by the action of the thread.

Where the hole or cut-out for the locking pin is a through hole, the locking pin may be drawn out in the same way, the screw being driven after it hits a solid surface behind the nut. Both a through hole and blind hole may be provided in each case, for use in either of the above described modes.

The locking pin may be curved along its elongate extent, with the cutting tooth on the convex curved side of the pin. When such a locking pin is inserted, any protruding portion will be curved away from the thread, facilitating removal with pliers or similar.

The profile of the pin body may be substantially rectangular, and the profile of the cutting tooth may be substantially triangular. One or more of the edges of the cutting tooth may alternatively curve towards an apex. A rectangular profile allows for easy positioning of the pin body with the cutting tooth facing into the thread. The cutting tooth may be disposed substantially at the centre of one of the faces of the rectangular profile section of the pin body, or two cutting teeth may be provided, one at each edge of one of the faces of the rectangular profile section of the pin body.

According to a third aspect of the present invention, there is provided a threaded component for use with a locking pin according to the second aspect of the invention, in which a hole or cut-out is provided in the component parallel to the axis of the thread, and at least in part intersects with the thread.

The hole or cut-out may pass all the way through the threaded component, or may be a blind hole.

The threaded component (which may be, for example, a nut), may be screwed onto a second threaded component (for example, a bolt). A locking pin according to the second aspect of the invention may then be driven into the hole or cut-out, preventing rotation of the threaded components relative to each other.

A plurality of similar holes or cut-outs may be provided in the threaded component, spaced around the circumference of the thread. Providing a plurality of similar holes or cut-outs means that a hole or cut-out is always likely to be exposed for inserting a locking pin according to the second aspect of the invention, regardless of any obstructions which may be present in the installation environment. A threaded hole may be provided adjacent to and continuous with the hole or cut-out. Once a locking pin has been inserted into the hole or cut-out, a retaining screw may be driven into the threaded hole in order to hold the locking pin in position. The retaining screw engages with a screw thread portion or elastically deformable portion provided on the locking pin, as described above. The threaded hole may be a blind hole or a through hole. When it is desired to remove the locking pin, the retaining screw is removed.

An untapped hole may alternatively be provided in place of the threaded hole, the retaining screw gripping only onto a screw thread portion or elastically deformable portion of the locking pin. The untapped hole may be a blind hole or a through hole. Where the hole is untapped, continued rotation of the screw once it will no longer drive further into the hole will serve to draw the locking pin out of its hole or cut-out. A hole for a screw or other retaining member may alternatively be provided perpendicular to and intersecting the hole or cut-out for the locking pin.

The threaded component according to the third aspect of the invention may be a nut, a bolt, or any other male or female threaded component.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which:

Figure 1 is a plan view of a nut according to the third aspect of the invention;

Figure 2 is a perspective view of a locking pin according to the second aspect of the invention, for use with the nut of Figure 1;

Figure 3 is a plan view of a second embodiment of a nut according to the third aspect of the invention; Figure 4 is a perspective view of a second embodiment of a locking pin according to the second aspect of the invention, for use with the nut of Figure 3;

Figure 5 is a side view of the locking pin of Figure 4; Figure 6 is a plan view of a third embodiment of a nut according to the third aspect of the invention;

Figure 7 is a perspective view of a third embodiment of a locking pin according to the second aspect of the invention, for use with the nut of Figure 6; Figure 8 is an alternative perspective view of the locking pin of Figure 7;

Figure 9 is a perspective view of a fourth embodiment of a locking pin according to the second aspect of the invention, also for use with the nut of Figure 6;

Figure 10 is an alternative perspective view of the locking pin of Figure 9;

Figure 11 is a perspective view of the nut of Figure 1 attached to a bolt;

Figure 12 is a perspective view of a locking element according to the first aspect of the invention;

Figure 13 is a perspective view of a shaft for use with the locking element of Figure 12;

Figure 14 is a perspective view of the locking element of Figure 12 installed on the shaft of Figure 13; Figure 15 is a perspective view of a second embodiment of a locking element according to the first aspect of the invention;

Figure 16 is a perspective view of the locking element of Figure 15, shown together with a corresponding shaft;

Figure 17 is a perspective view of the locking element of Figure 15, installed on the shaft of Figure 16;

Figure 18 is a perspective view of the locking element and shaft of Figure 17, shown with a rotating machine part;

Figure 19 is a perspective view of a third embodiment of a locking element;

Figure 20 is an alternative perspective view of the locking element of Figure 19; Figure 21 is a perspective view of the locking element of Figure 19, together with a corresponding shaft; Figure 22 is a perspective view of a fourth embodiment of a locking element;

Figure 23 is a perspective view of the locking element of Figure 22, together with two corresponding shafts of different diameters; and Figure 24 is a plan view from one end of the locking element and shaft of Figure 23.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring firstly to Figure 1, a threaded nut is generally indicated at 10. The nut is of a conventional type, being of hexagonal shape with six bearing surfaces for a spanner to apply a force to the nut and two opposing faces. The major diameter of the thread is indicated by phantom line 12, and the minor diameter by line 14.

Three circular holes 16 are provided through the nut, from one face to the other. The holes are substantially parallel to the bearing surfaces of the nut, and to the axis of the thread. Each of the holes extends partially through the thread, to a point around half way between the major axis 12 and the minor axis 14. The holes are spaced at equal intervals around the nut, so that at least one hole is likely to be easily accessible in whatever position the nut is in when it is tightened, considering that various obstructions may be present in a typical installation environment. It will be understood that any number of holes may be provided in different embodiments, including only one hole.

Referring now to Figure 2, an elongate locking pin is indicated generally at 20. The locking pin 20 shown has an elongate extent similar to the distance between the opposing faces of the nut 10, although different lengths of locking pin may be used. The pin 20 is in the form of a hollow cylindrical tube having a longitudinal slot down the entire length. The pin is made from a hard material, and includes a cutting edge 22 at one end. The cutting edge is provided with a lead, to aid positioning of the pin in a hole before striking with a hammer. The pin may be sprung so that it will fit tightly in a hole of slightly smaller diameter than the diameter of the pin at rest.

In use, the nut 10 is screwed onto a bolt or other male threaded member. Once the nut 10 is in the required position, the locking pin 20 is introduced into one of the holes 16 with the cutting end leading into the hole. Any of the three holes 16 may be used, depending only on which is in the most convenient position in each particular in-use situation. The locking pin 20 is driven into the hole 16 by applying force with, for example, a hammer. The cutting edge 22 of the locking pin 20 cuts through approximately half of the width of the thread of the male threaded member. The locking pin 20 remains in the hole 16, thereby preventing rotation of the nut.

Where it is anticipated that the nut may in due course need to be removed or adjusted, a portion of the locking pin 20 may be left protruding from the nut, so that it may be removed with, for example, pliers.

The cutting edge 22 of the locking pin 20 is sharp, resulting in a clean cut through the thread with no substantial burring. As a result, damage to the male thread is minimised and the nut is able to freely rotate after removal of the locking pin 20.

The bolt or other male threaded member may be reused several times, since only a small portion of the thread is cut away each time the nut is locked, and the cleanness of the cut means that the operation of the thread will not be adversely affected. The nut may also be reused several times. It is suggested that the locking pin 20 is used only once, since the cutting edge 22 will inevitably become slightly blunted, which in further use may result in an unclean cut, damaging the thread of the male threaded member. However, where the locking pin 20 is made from a hard material, and the male threaded member is relatively soft, the locking pin 20 may be reused several times. For example, a hardened steel locking pin may cut a brass thread without being substantially blunted.

Referring now to Figure 3, a second embodiment of a lockable threaded nut is indicated generally at 30. Like the nut 10, the nut 30 includes six bearing surfaces, two opposing faces, and a thread with major diameter 32 and minor diameter 34. In this embodiment, a curved cut-out 36 is included, forming an additional part of the same aperture through which a bolt is usually passed. The cut-out 36 passes through the nut from one face to the other, cutting entirely through a portion of the thread. A circular threaded hole 38 is provided adjacent to the cut-out 36, on the outer side of the cut-out and substantially at its centre, again forming part of the same aperture.

Although in this embodiment the circular hole 38 is threaded, it is envisaged that an untapped hole could instead be provided. Referring now to Figures 4 and 5, a second embodiment of a locking pin is indicated at 40. The locking pin 40 is curved perpendicular to its elongate extent to match the curve around the thread of the nut 30. The locking pin 40 therefore has a convex curved face and a concave curved face. A plurality of cutting teeth 42 is provided on the concave face. Like the locking pin 20, locking pin 40 is introduced into the cut- out 36 in nut 30 to cut through the male thread on a bolt or other threaded member. The locking pin 40 includes a portion of a female thread 44 on its convex curved face and, when the locking pin 40 is inserted into cut-out 36, the thread portion 44 completes the female thread in the hole 38 of the nut 30. A grub screw may then be inserted into threaded hole 38 to assist in retaining the locking pin 40 in the cut-out 36. Instead of providing a screw threaded portion 44, the locking pin 40 may have an elastically deformable material, for example nylon, on its convex curved face, into which a thread may be cut by a screw as it is inserted. This alternative has the advantage that the locking pin 40 does not have to be positioned so that thread portion 44 exactly corresponds to the thread in hole 38. It should be understood that the screw threaded portion 44 or soft portion as described above may be realised on any of the embodiments described herein, and in other embodiments of the invention which will be apparent to the skilled person.

Referring now to Figure 6, a third embodiment of a lockable threaded nut is indicated generally at 50. Like the nut 10, the nut 50 includes six bearing surfaces, two opposing faces, and a thread with major diameter 52 and minor diameter 54.

A cut-out 56 is provided through the nut 50, from one face through to the other. The cut-out 56 is substantially rectangular, and extends from the minor diameter 54 of the thread. Like the nut 10, cut-outs may be provided in a number of locations around the circumference of the nut so that a cut-out is accessible despite any obstructions which may be present in a typical installation environment. Referring now to Figures 7 to 10, locking pins 60, 70 are designed to be inserted into cut-out 56 in nut 50. The locking pins have a substantially rectangular profile, with at least one cutting tooth 62, 72. The cutting tooth has a triangular profile, and extends along an elongate extent of the locking pin, and may be tapered at one end 64. A threaded hole 66, 76 is provided through the locking pin 60, 70.

Locking pin 70 has cutting tooth 72 extending from the centre of one of the faces of the rectangular profile pin body, and locking pin 60 has cutting teeth 62 extending from either side of one of the faces of the rectangular profile pin body. The taper 64 allows the locking pin 60, 70 to be easily seated in cut-out 56. Once the locking pin 60, 70 is seated in cut-out 56, it may be struck with a hammer or similar tool. The cutting tooth 62, 72 cuts through the male thread of the bolt or other threaded member to which the nut 50 is attached. Although a tapered cutting edge is shown only on locking pin 60, the tapered edge may equally be applied to locking pin 70, locking pins 40 and 20, and to other embodiments which will be apparent to the skilled reader.

Force may be applied to locking pin 60, 70 until it has been moved all the way into the cut-out 56 in nut 50, leaving no substantially protruding portion. In this case removal of the locking pin 60, 70 may be effected by introducing a screw into hole 66 or 76 in the top of the locking pin 60, 70. The screw may then be gripped with pliers, and the locking pin 60, 70 pulled away. Any of the locking pins 20, 40, 60, 80 may be curved along their elongate extent so that, when inserted, a protruding portion points away from the bolt or other threaded member. This assists removal with, for example, pliers since access to the protruding portion of the locking pin will be easier than for a straight locking pin. Although all of the above described embodiments have holes or cut-outs in a female threaded nut, the skilled reader should understand that, in appropriate circumstances (for example where obstructions in the installation environment demand it), holes or cut-outs may alternatively be provided through a bolt or other male threaded member, the locking pin, in use, cutting through the thread of a nut or other female threaded component. It will also be apparent to the skilled reader that female threaded components other than nuts may be provided with holes in the manner described.

In use, and as shown in Figure 11, any of the above-described nuts 10, 30, 50 may be screwed onto a bolt 100 or other threaded member. Once the nut 10, 30, 50 is in the desired position, the appropriate locking pin 20, 40, 60, 70 is inserted into the hole or cut-out 16, 36, 56, and is struck with a hammer or similar. The locking pin 20, 40, 60, 70 will then make a clean cut through the thread of the bolt 100, holding the nut in position.

It is noted that a nut will typically be tightened against a surface of, for example, a machine part. In this case, the nut when tightened will result in a constant tensile stress in the bolt. This stress or "preload" forces the nut against the surface of the machine part, and there is therefore substantial friction between the nut and the machine part, discouraging loosening. However, where the fixture is subject to vibration, the tensile stress in the bolt will be variable, and loosening may occur. Providing a locking pin as described mitigates this problem, preventing loosening. There may also be situations, as illustrated in Figure 11, where the nut 10 is not tightened against any bearing surface. There is therefore no friction on the face of the nut preventing loosening, and only the locking pin prevents the nut from turning.

Referring now to Figure 12, a locking element for coupling a shaft to a rotating part is indicated generally at 80. The first face 82 of the locking element is in the shape of a segment of a circle, having a rectangular section protruding from the centre of its curved side. The second face of the locking element is a copy of the first face, being translated in a direction perpendicular to the plane on which the first face lies. Two further curved faces 84, 85 and four flat faces join corresponding sides of the first and second faces. The three-dimensional locking element therefore has a first portion which is a horizontal cylindrical segment and a second portion which is a cuboid. In use and as shown in Figures 13 and 14, a portion in the shape of a horizontal cylindrical segment is milled out of the centre of a shaft. The locking element may then be placed on top of the flat surface of the shaft, where the portion has been milled away. A rotary part such as a cog, having a rectangular keyway, is then slid over the shaft, and engages with the shaft via the locking element so that the cog cannot rotate with respect to the shaft.

Figure 15 shows a second embodiment of a locking element 90, similar to the first embodiment 80 and having a first face 92, a second face which is a translated copy of the first face and four further flat faces and two further curved faced. The locking element 90 is provided with a tang 98 extending from the flat surface of the key which joins the sides of the first face 92 and the second face which are chords of the circle segments. The tang 98 is provided adjacent to an edge of that side which is a chord of a circle segment, and is substantially rectangular in shape. Although the tang 98 in this embodiment is adjacent an edge, the tang 98 may be provided at any position between the first face 92 and the second face.

The locking element 90 with the tang 98 is used where it is desired to attach a rotating part such as a cog 120 to the end of a shaft 110, as illustrated in Figures 16 to 18. The locking element 80 of Figure 12, without a tang, is used where a part needs to be attached other than at an end of the shaft 112. The tang prevents any possible longitudinal sliding of the locking element along the shaft. Referring now to Figures 19 to 21, a third embodiment of a locking element is indicated at 130. The locking element 130 is the same general shape as locking elements 90, 100, and includes a first face 132, a second face which is a translated copy of the first face, two further curved faces 134, 135 and an underside 136. This embodiment also includes a tang 138. A V-shaped groove 140 is provided along a central length of the underside 136, substantially opposite the portion of the locking element which forms a cuboidal section.

In Figure 21, the locking element 130 is shown in use with a shaft 142. The shaft 142 includes a threaded hole 144 through its centre. The size of the hole is such that, when a section of the shaft 142 is milled away to install the locking element, there is only a very thin layer of material left on the shaft at the centre of the milled-away section. The locking element 130 with a V-groove 140 is advantageous for use with this type of shaft, because the V-groove ensures that force is not applied to the shaft at the centre of the milled-away area, which may be weaker because the material is thin. Also, if a bolt or other threaded member is screwed into the hole 144, there is a possibility that the centre of the milled away area will deform slightly. Providing a locking element with a V-groove ensures that the locking element will fit onto the shaft in this case.

Referring now to Figure 22, a fourth embodiment of a locking element is indicated generally at 150. The locking element 150 is generally a similar shape to the previously described locking elements, again having a first face 152, a second face which is a translated copy of the first face, and two curved faces 154, 155. However, the curved faces 154, 155 of this locking element each include a main curve, defining a convex surface, with a secondary curve in the other direction, that is, defining a concave surface, interrupting the main curve and forming an indent in the convex surface. The double-curve design allows the locking element 150 to be used with shafts of various different diameters 160, 161. Figure 23 shows two such shafts, with sections milled away for use with locking elements. As shown in Figure 24, when the element 150 is fitted to a smaller sized shaft 160, the distal edges of the curved surfaces 154, 155 protrude over the edges of the milled-away section of the shaft. These protruding sections need to be filed or ground off, but this is an easy job because the material is thin at the distal edges, due to the double-curved shape. The amount of material to be removed is therefore minimised.

The locking element is advantageous since the only machining that is required on the shaft is the removal of an entire horizontal cylindrical segment. This is considerably easier and less time-consuming to achieve than milling a conventional key seat in the shaft. A slot for the tang may also need to be milled into the shaft, but again this is a simple operation since material is removed all the way from one side of the piece to the other, and the slot is parallel sided, i.e. rectangular. The embodiment with a V- shaped groove is particularly suitable for shafts with a longitudinal hole through them, and the embodiment with double-curved surfaces ensures that a single element can be used with shafts having a variety of different diameters.

The locking element is particularly useful in applications where a key-seat needs to be repaired, because the shaft or other drive member can be milled flat to retain the locking element, which is usually relatively straightforward.

It will be understood that the embodiments shown are given by way of example only. In particular, the skilled person will appreciate that it is possible to include the features of a tang, a groove and double-curved surfaces in any combination. The tang may be of rectangular profile but could also be other shapes, for example triangular or curved. Likewise, the groove need not be V-shaped, but could be rectangular or curved.