REMOVABLE SHARPENING GUIDE Technical Field The present invention relates to a sharpening guide for holding a knife. 5 Background Art Any discussion of the prior art throughout the specification is not an admission that such prior art is widely known or forms part of the common general knowledge in the field. 10 Hand steels are commonly used tools for sharpening knives both commercially and domestically. Use of the steel relies on the user's skill to form and maintain the angle between the knife blade and the hand steel. Thus, inexperienced or infrequent users of the steel find it difficult to hold the blade of the knife at the desired angle for sharpening. It is important to maintain the same angle during sharpening, to ensure the knife is well 15 sharpened. Mechanisms for aiding the user in maintaining a desired sharpening angle have previously been proposed, including the guide described in US 2006/0141916 Al. This patent application discloses a knife sharpener which comprises an elongated sharpening 20 member extending through a sharpening guide. A spring is fixed at one end of the sharpening member, extending for a distance along the sharpening member, before terminating at the sharpening guide. This configuration allows longitudinal movement of the guide portion in both directions along the length of the sharpening member. The guide portion includes at least one slot, which is configured to position the knife blade in contact 25 with the sharpening member at a predetermined angle. However, this guide is highly restrictive for users. The use of slots to angle the knife blade does not allow for the natural sweeping motion of the blade seen when a user sharpens a knife on a steel without such a guide. As such, although the guide aids in maintaining a 30 predetermined angle, sharpening is slower, as the user must take time to carefully position the blade in the slot before sliding the blade against the sharpening member. Furthermore, the slots do not allow for blades of varying thicknesses to be used. To overcome this disadvantage the document proposes that a number of interchangeable guide portions be available so that blades of varying thicknesses may be sharpened. 35 1 When using a hand held sharpening device the user generally moves both the knife and the sharpening device at the same time, allowing for a smooth sharpening action. This smooth sharpening action is not possible with the sharpening devices shown in US 2006/0141916 as ali are fixed/resting on a surface; this forces a user to have a fixed 5 surface upon which to rest the knife sharpener and effectively prevents the knife sharpener from moving. It would be beneficial if a removable sharpening guide in the form of an adapter for a hand steel could be devised, which overcomes at least some of the deficiencies in the prior art, i or at least provides a useful choice It would also be beneficial if such a guide could be used with blades of varying thicknesses and also be suitable for use by both experienced and inexperienced users. Disclosure of Invention 15 The present invention relates to a sharpening guide for a hand steel, wherein the sharpening guide includes a base portion and a guide portion releasably connected to, and spaced apart by, a biasing means, and: the base portion is a body of rigid material which includes a first hole; the guide portion is a body of rigid material which includes an open V-shaped cut 20 out and a second hole; the V-shaped cut-out is located at a first end of the guide portion, where the first end is coterminous with one terminal end of the sharpening guide; and - the second hole passes through a vertex of the V-shaped section with a centreline of the second hole extending between two walls of the V-shaped cut-out; 25 such that the V-shaped cut-out is configured to support a knife blade at a predetermined angle to the centreline of the second hole. The V-shaped cut-out may be symmetrical or asymmetrical. 30 Preferably the first hole is configured to fit around the shaft of a hand steel in a snug fit. Preferably the second hole is configured to fit around the shaft of a hand steel in a close clearance fit. 2 Preferably the angle between the centreline of the second hole and either wall of the V shaped cut-out is between 52 and 552. Preferably the biasing means is a spring. 5 Preferably the spring is attached to each of the guide portion and the base portion by means of annular protrusions extending from the first and second holes. Alternatively, the spring is attached to each of the guide portion and the base portion by 10 means of annular recesses located at ends of the first and second holes. Preferably the guide portion is configured to be located in use on a steel no more than two-thirds of the distance between the grip of the hand steel and a tip of the shaft of the hand steel, and no less than 40mm from the tip of the shaft of the hand steel. 15 Preferably the base portion and the guide portion are made from a food-grade plastic. Brief Description of Drawings By way of example only, a preferred embodiment of the present invention is described in 20 detail below with reference to the accompanying drawings, in which: Figure 1 shows a perspective drawing of the sharpening guide fitted to a hand steel with a knife as positioned in use; Figure 2 shows a side view of the guide portion and a cross-section of a blade as positioned during use; 25 Figure 3 shows a top view of the guide portion. Figure 4 shows a vertical cross-section of the guide portion. Figure 5 shows a vertical cross-section of a first embodiment of the base portion. Figure 6 shows a vertical cross-section of a second embodiment of the base portion. Figure 7 shows a top view of the first embodiment of the base portion. 30 Definitions As used herein, the terms listed below have the following meanings: Hand Steel - A knife steel or a knife sharpening steel that is intended to be held in one hand when manually sharpening a knife. Can also be called a honing steel 35 or a butchers steel. 3 Snug Fit - a fit (as of mechanical parts) with no allowance: the closest fit that can be assembled by hand for parts that are not to move against each other. Best Mode for Carrying Out the Invention 5 Referring to Figure 1, a sharpening guide (10), which includes a base portion (15), a spring (17), and a guide portion (18), is shown in use with a hand steel (11). As can be seen in this Figure, the spring (17) connects the base portion (15) to the guide portion (18), and when in use the base portion (15) is located adjacent the grip (13) of the steel. The sharpening guide (10) is configured to be removably attached around the 10 shaft (12) of the hand steel (11). The base portion (15) holds the sharpening guide (10) in place on the shaft (12), as its first centrally aligned hole (16), which is shaped to correspond with the cross-section of the shaft (12), is dimensioned to have a releasable snug fit around the shaft (12). The 15 snug fit also prevents rotation of the sharpening guide (10) when in use. The base portion is a body of rigid material through which the hole (16) is bored. The base portion (15) as shown in the drawings is of circular cross-section, however it may be of any cross-section. The spring (17) extends from the base portion (15) longitudinally along the shaft (12) of 20 the hand steel (11), and is coiled around the shaft (12), terminating at the guide portion (18). The guide portion (18) is a body of rigid material through which a second centrally located hole (20) is bored. A V-shaped cut-out is located at one end of the second hole (20), the 25 second hole (20) terminating in the apex of the 'V' (as can be seen in Figure 3 and Figure 4). The attachment point of the spring (17) is located at the opposite end of the second hole (20). The second hole (20) is dimensioned to fit around the shaft (12) of the hand steel (11) in a 30 "close clearance fit", that is, the guide portion (18) is allowed to freely slide along the longitudinal axis (marked 'A' in Figure 1), but not in a direction perpendicular to this axis. The guide portion (18) is configured so that the shaft (12) of the steel (11) extends from the second central hole (20) at the apex of the 'V', and between the two walls (23, 24) of the 'V'. The length of the spring (17) is such that the guide portion (18) is located no more 35 than two-thirds of the way up the shaft (12) of the steel (11) from the grip (13), or no less 4 than around 40-50mm from the tip (14) of the steel (11), to allow room for a knife to come into contact with the steel. The open V-shaped cut-out (22) of the guide portion (18) accommodates the natural 5 stroke of the user, providing an advantage over other known sharpening guides. In use, the user places the blade (30) against the steel (11) between the guide portion (18) and the tip (14) of the steel, then allows the blade (30) to fall into place against a wall (23, 24) of the V-shaped cut-out (22). This aligns the blade (30) at the desired angle in relation to the steel (11). Keeping in contact with the wall (23, 24), the blade (30) is then drawn 10 through the guide portion (18), sliding against the steel (11). The user puts pressure on the guide portion (18), compressing the spring (17). As the blade (30) is drawn through the guide portion (18) from hilt to tip, this pressure eases, and the spring (17) expands, pushing the guide portion (18) back towards its resting position. 15 Figure 2 shows a cross-section of a knife blade as positioned when in use. As can be seen in this Figure, the angle (x 2 ) between the steel (11) and the knife blade (30) is determined by the angle of the V-shaped cut-out (22). The guide portion (18) may be manufactured so that this is any angle. Ideally the angle between the steel (11) and a wall (23, 24) of the V-shaped cut-out (22) is between 52 and 552. It is not necessary for the V 20 shaped cut-out to be symmetrical, i.e. the angles x 1 and x 2 shown in Figure 2 need not be equal. The distance 'L' marked on Figure 2, i.e. the length of a wall of the V-shaped cut-out (22), is ideally approximately as long as the depth of the knife blade (30). If the distance 'L' is 25 much shorter than the depth of the blade (30), the blade (30) may fall sideways off the guide portion (18), posing a risk of injury to the user. As is shown in Figure 1, an end of the spring (17) is coiled around an annular protrusion (40) which extends from the base portion's central hole (16). This embodiment 30 of the base portion (18) is shown in vertical cross-section in Figure 5 without the spring (17). In an alternative embodiment, the base portion (15) does not include the annular protrusion (40), and instead includes an annular recess (42) at one end of the base portion's central hole (16), as shown in vertical cross-section in Figure 6. In this alternative embodiment, an end of the spring (17) is inserted into the annular recess (42). 35 5 It will be appreciated that the corresponding location where the spring attaches to the guide portion (18) may also be an annular protrusion or an annular recess. It will also be appreciated that these are preferred means for attaching the spring (17) to the guide portion (18) and base portion (15), and other means for attaching a spring to the guide 5 portion (15) and base portion (18) may be used without altering the inventive concept of the sharpening guide (10). Although in the preferred embodiment the guide portion and the base portion are connected by a spring, any biasing means may be suitable in place of the spring. The 10 biasing means functions to maintain the guide portion at a desired point along the shaft of the steel and to return the guide portion to this point after the biasing means has been compressed during the stroke of the knife blade. Both the guide portion (18) and the base portion (15) may be made from a food-grade 15 plastic such as nylon or polyethylene. 6