Snooker tables, and tables for playing related games such as billiards and pool, are of course well known. Such tables can be used as dining tables, by resting a cover on the cushions of the table, but the dining table formed by doing this is generally not at a convenient height for dining, as the surface of the dining table is normally too high. The height difference is normally around 75mm (3 inches).

Mechanisms are known for adjusting the height of the surface of the table, thus allowing the table to used both as a snooker table (or a billiards or pool table) and as a dining table. When it is desired to convert the table to a dining table, the height of the bed of the table is lowered, and a cover is laid across the cushions.

A prior art height adjusting mechanism 110, which has been known for many years, is shown in Figure 1.

This prior art mechanism includes a first part 112, which is connected to the frame of the table, and a second part 130 which is connected to the bed. The parts are shown separated for clarity. As can be seen, the first part 112 comprises a generally flat member 114, which is normally formed from a metal such as brass. A number of grooves 116 are formed on a face of the flat member. The member is also formed with holes 118 for screws or the like, allowing it to be attached to a support frame of the table.

The second part 130 is formed to engage with the first member so that it can slide relative to the first

member in the direction A-A. The second part also comprises a peg 132 for engaging in the grooves 116 on the first part 112. The peg 132 can slide in a slot 134 formed in the second part, the slot extending transverse to the direction A-A. The second part 130 also has a part 136 allowing it to be connected to the underside of a bed of a snooker table.

The operation of the prior art height adjusting mechanism 110 will now be briefly discussed. When the bed is in its lifted (playing) position, the peg 132 of the second part 130 engages in a detent 120, and is retained therein by the weight of the bed urging it downwardly.

When it is desired to move the bed to its lowered (dining) position, it is necessary to lift the bed, so that the peg 132 is lifted from the detent 120. The peg 132 comes into contact with a rib 122, which urges it sideways in the slot 134. The bed is then lowered, and the peg moves downwardly in groove 124 to the side of the detent 120. This movement of the peg 132 past the detent 120 allows the bed of the table to be lowered.

When it is desired to move the bed back to its lifted (playing) position, the bed is again lifted. The peg 132 now moves along groove 126, and at the top of the groove is urged sideways in the slot by rib 128.

The bed is then lowered, so that the peg 132 enters detent 120.

One problem with the prior art height adjusting mechanism 110 is that the peg 132 is moved in the slot 134 purely by contact with the grooves and ribs of the first part. It is possible for the peg to"jam"during the lifting or lowering process; for example, it can come into direct contact with the lowermost part of rib 122, and not be moved sideways as a result of this contact. If this occurs, it is necessary to move the bed laterally with respect to the frame, to attempt to dislodge the peg, which can be difficult as the beds of snooker tables normally have a considerable mass.

Further, the prior art height adjusting mechanism must be mounted directly between the support frame of the table, to which the legs of the table are attached, and the bed. This can cause problems if the bed is particularly thick, as is the case if the table is used for playing pool and includes a ball-return mechanism.

According to the invention, there is provided a position adjustment mechanism, comprising two cylindrical portions, a first one of the portions being slidably disposed inside a second one of the portions, wherein one of the portions has a detent and the other portion has a member for engaging in said detent to hold said portions in a first position, the member being removable from said detent to allow said portions to move into a second position.

Preferably, the portions are biassed away from each other by a resilient means. The use of cylindrical portions allows the provision of such resilient means positioned between the portions. These resilient means tend to urge the portions apart, and this helps prevent the mechanism from jamming.

Preferably, the detent is upwardly open. The member can then be retained in the detent by gravity.

In a preferred form, the detent is formed on the first portion, and the member is formed on the second portion. It is preferred for the detent to form part of a groove formed on the first portion, with the member engaging in the groove.

In a preferred form, the groove forms a circuit, and the member moves around the circuit as the portions move from their first position to their second position and back to their first position.

It is further preferred for there to be a plurality of grooves, and a corresponding plurality of members.

This reduces the chance of the mechanism jamming.

Preferably, one of the portions is in contact with a first body and the other of the portions is in contact with a second body, with motion of the portions between

the first position and the second position serving to adjust the vertical distance between the bodies.

A preferred embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a view of a prior art height adjustment mechanism; Figure 2 is a perspective view of an embodiment of the height adjustment mechanism of the invention; and Figures 3a to 3c are perspective views of parts of the mechanism shown in Figure 2.

As shown in Figure 2, the preferred embodiment of the height adjustment mechanism 10 comprises two main parts, a first portion 12, which in this embodiment has a foot 18 for engaging a floor, and a second portion 50 for connection to a snooker or pool table.

The first portion 12 comprises two parts, a floor- engaging part 14 shown in Figure 3a and a grooved member shown in Figure 3b.

The floor-engaging part comprises a foot 18 for resting on the floor, and a threaded rod 20 extending upwardly from the centre of the foot.

The grooved member is in the form of a cylinder 22, with a threaded bore formed 24 in its lower face. The threaded rod 20 engages in the threaded bore 24, and the rod can be screwed into and out of the bore for fine adjustment purposes.

In addition, the central region of the cylinder 22 has an upwardly-open hollow 26 therein to accommodate a spring, which will be described in more detail later.

A groove 28 is machined into the outer cylindrical surface of the cylinder 22, surrounding an"island"30.

The groove 28 will be described in more detail later with reference to the operation of the height adjusting mechanism. While it is possible to use a single groove, it is preferred that a plurality of identical grooves are formed, equispaced around the cylinder, and it is particularly preferred to use three grooves.

The second portion 50, shown in Figure 3c, is in the form of a hollow cylinder 52, whose inner diameter is slightly greater than the outer diameter of the cylinder 22 of the first portion. The hollow cylinder 52 is adapted for connection to a snooker or pool table, and may for example fit into a recess formed on the underside of the support frame of the table. It may also be positioned in the top or bottom of a leg of the table. The embodiment described is intended to fit into the bottom of a leg.

In the assembled state of the height adjustment mechanism, the cylinder 22 fits inside the hollow cylinder 52, as shown in Figure 2. This fit must be tight, to prevent lateral movement of the bed of the table. Additional grooves 44 can be formed on the outside of the cylinder 22 along its length, to allow the passage of air into and out of the central part of the hollow cylinder. If these grooves are not provided, and the fit between the cylinders is sufficiently close, then the mechanism may"lock"as a result of pressure difference between the outside and the inside of the mechanism.

At least one bore 54 is formed through the hollow cylinder, towards its lower end, and a peg 56 is fitted into the bore. The length of the peg 56 is such that it projects into the hollow central region of the hollow cylinder 52, the projecting length being slightly less than the depth of the groove 28 machined into the cylinder 22 of the first portion, so that the peg 56 can engage in the groove 28. The number of bores and pegs is the same as the number of grooves.

A spring is positioned between the hollow cylinder 52 of the second portion and the cylinder 22 of the first portion. This spring serves to bias the portions apart, and therefore tends to push the cylinder 22 out of the hollow cylinder 54.

The operation of the height adjusting mechanism will now be described.

When the bed is in its lifted (playing) position, the peg 56 engages in a detent 32 formed at the upper end of the"island"30. The peg 56 is retained therein by the weight of the bed urging it downwardly, and also by the spring urging the cylinder 22 out of the hollow cylinder 52.

When it is desired to move the bed to its lowered (dining) position, the bed is lifted, and the peg 56 is lifted from the detent 32. The peg 56 comes into contact with a rib 34, and exerts a sideways force on it. As a result of this force, the cylinder 22 is forced to rotate in the hollow cylinder 52. Further, the presence of the spring also serves to urge the cylinder and the hollow cylinder apart, which prevents the peg 56 from jamming in the groove. In addition, the preferred embodiment uses three pegs moving in three grooves, and it is extremely unlikely that all three pegs will jam simultaneously; if one peg jams, the force exerted on the other pegs will tend to unjam it.

The peg 56 moves to region 36 of the groove (although it will be appreciated that this movement of the peg is partly achieved by the groove moving relative to the peg as the cylinder 22 rotates).

The bed is then lowered, and the peg 56 moves downwardly in groove 38 to the side of the detent 32.

This movement of the peg 56 past the detent 32 allows the bed of the table to be lowered. During this motion, the spring is compressed.

When it is desired to move the bed back to its lifted (playing) position, the bed is again lifted. The peg now moves along groove 40, and at the top of the groove the peg 56 is moved sideways relative to the groove by rib 42. Again, it will be appreciated that this sideways movement is achieved by the cylinder 22 rotating in the hollow cylinder 52. Further, it will also be appreciated that the presence of the spring urging the cylinder and the hollow cylinder away from each other, and the presence of a plurality of pegs and

grooves, helps to prevent the peg from jamming. The bed is then lowered, so that the peg 56 enters detent 32.

Fine adjustment of the height, to ensure that the surface of the table is level, can be achieved by rotating the foot 18 relative to the cylinder 22, thus screwing the threaded rod 20 in and out of the threaded bore 24.

It will be appreciated from the above that at least the preferred embodiment of the height adjustment mechanism is much less prone to jamming than the prior art mechanism. Further, the preferred embodiment of the height adjustment mechanism does not need to be positioned directly between the frame and the bed, thus allowing a greater freedom for the designer. Indeed, the mechanism can be fitted directly between the legs and the bed, thus avoiding the requirement for a frame.

Of course, if the mechanism is not fitted into the bottom of the legs of the table, then there is no need for the mechanism to include a fine adjustment mechanism, as described. Instead, a separate fine adjustment mechanism can be installed in the bottom of the leg, to allow the table to be levelled.

It will also be appreciated that a number of variations can be made to the height adjusting mechanism. For example, the arrangement of the pegs and grooves could be reversed, so that the pegs are carried on the cylinder and the grooves are formed on the hollow cylinder. Further, although the height adjustment mechanism has been described in the context of snooker, pool and billiard tables, it can of course be used in other situations.