Joint between tubes of a tube combination having annular trenches

A tube combination has upper and lower tubes, which are joined together with a coupling, and which have spaced annular trenches on outer sides. Annular projections are formed on the upper end of the lower tube and the lower end of the upper tube; the annular projections are pressed against each other when the tubes are joined together, and are shaped such that they together are in the shape of the annular trenches when the tubes are joined together, making the tube combination look like one having a single tube part.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to a tube combination, more particularly a tube combination, which has a coupling for connecting two tube parts thereof together, which is relatively easy and safe to use and relatively economical to manufacture.

2. Brief Description of the Prior Art

Steel tubes are widely used on furniture such as beds, desks, racks, and chairs because they are light in weight and can be easily shaped. Early conventional steel tubes were not formed with ornamental designs on the cylindrical surfaces therefore they can't match other parts of furniture. To make steel tubes look attractive and match other parts of furniture, annular trenches are formed on the steel tubes. The annular trenches can also help other parts of furniture located when they are joined to the steel tubes.

Referring toFIGS. 7,8, and9, a tube combination has a coupling42, upper and lower tubes41,41, which have spaced annular trenches411on the outer sides and threads on inner sides of two ends, and are joined together by means of the coupling42; the coupling42has threads421,421on outer sides of upper and lower ends, and a middle rim422, which is made with such a shape as to make the joint between the tubes41,41look like the trenches411when the coupling42are connected to the tubes. And, when the tube combination is joined to grilles43to form a rack, as shown inFIGS. 8 and 9, connecting tube elements432of the grilles43, which have annular protrusions433on inner sides, can engage selected ones of the annular trenches on the tube combination easily. In other words, the grilles43can be easily located and secured in position owing to the annular trenches. However, the tube combination is found to have disadvantages as followings:1. The coupling42is costly to manufacture because it is formed with threads421on two ends, and a middle rim422, which is bigger than the threaded ends in diameter, and in turn, the coupling42has to be made by means of cutting deeply into the curved surface of a cylindrical element with a lathe, cutting a lot of portions out of the cylindrical element. Furthermore, the coupling42has to be made of a material of solid cylindrical shape instead of a hollow cylindrical tube because the material has to have relatively big thickness for allowing the cutting as described above and because ordinary easily available tubes don't have such a big thickness. And, the cylindrical material has to be formed with a hole423. Consequently, a lot of portions are cut out of the material, and become waste.2. Manufacturing of the tube combination is difficult and labor-costing; a cylindrical material has to be formed with threads at two ends to become the coupling42, and both of the tubes41have to be formed with threads on the inner sides of the ends therefore relatively many cutting processes have to be performed, and in turn, manufacturing of the tube combination is costly.3. Assembly of the tube combination may cause injure to the persons performing the assembly; the users have to first hold a first threaded end of the coupling42to screw the other end into a tube41, and then screw the other end into the other tube therefore the users are prone to injure the fingers due to the sharp ends of the threads. Furthermore, the assembly is labor-costing because the coupling42has to be screwed into the tubes at both ends.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a tube combination, which has tube parts having spaced annular trenches on outer sides, and a coupling joining the tube parts together, such that a joint between the tube parts is in the shape of the annular trenches to make the tube combination attractive.

It is another object of the present invention to provide a coupling to tube parts of a tube combination, which is relatively economical to manufacture, and allows the tube parts to be easily joined together with it.

It is yet another object of the present invention to provide a coupling to tube parts of a tube combination, which is formed with threads on only a first end so that a user can first hold the other end, which has no threads formed on it, to screw the first end into one of the tube parts in assembly. Therefore, the user's fingers can't get injured with the threads.

It is still another object of the present invention to provide a coupling to tube parts of a tube combination, which is made of an easily available tube so that cost of manufacturing and material of the tube combination is reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIGS. 1, and2, a tube combination of the present invention includes upper and lower cylindrical tubes1,1, and a coupling2for joining the tubes together; the upper tube has spaced annular trenches11on an outer side, and threads12on an inner side of a lower end thereof; the lower tube has spaced annular trenches11on an outer side, an annular projection13sticking up from an upper end, and threads extending a relatively short distance on an inner side of the upper end; the coupling2is made by means of forming threads21on an outer side of a first end thereof, and has a second end22, which has no threads on it, and which is formed so that the outer diameter thereof is equal to the inner diameter of the lower tube1.

In assembly, one first holds the second end22, and screws the first threaded end of the coupling2into the lower end of the upper tube; a few lower ones of the threads21are not screwed into the lower end of the upper tube. Then, the second end22of the coupling2is passed into the upper end of the lower tube, and the lower ones of the threads21are screwed into the upper end of the lower tube. From the above description, it can be understood that the coupling2is much easier and less costly to manufacture than that of the prior art one as described in the Background because it can be made by only forming threads on one end of an easily available tube and cutting into the lower end22for only a relatively small depth. In addition, the coupling2is safe. to use, and the users won't injure the fingers because they don't have to hold the threaded portion of the coupling2when they are assembling the tube combination.

Referring toFIGS. 3, and4, a tube combination of the second embodiment includes a coupling3, and upper and lower tubes1,1having spaced annular trenches11formed on the outer sides; the coupling3is a cylindrical tube, of which the outer diameter is substantially equal to the inner diameter of the tubes1; the tubes have inner annular stopping protrusions14corresponding to the trenches11thereof. In assembly, the coupling3is inserted into a lower end of the upper tube and an upper end of the lower tube with two ends thereof being stopped by the inner protrusions14of the tubes1. Therefore, the tube combination is relatively easy to assemble.

Referring toFIG. 5, a tube combination of the third embodiment includes a coupling2the same as that of the first embodiment, and upper and lower tubes1,1, which have annular trenches11, and threads like those of the first embodiment. The upper and lower tubes1,1further have annular projections15,15sticking up from a lower end, and an tipper end respectively so that when they are joined together with the coupling2, the annular projections15,15form an annular trench, which is in the shape of the annular trenches11.

Referring toFIG. 6, a tube combination of the fourth embodiment includes a coupling2, which is the same as that of the first embodiment, and upper and lower tubes1,1, which have spaced annular notches11on the outer sides. The upper and lower tubes1,1further have annular projections16,16, which stick up from a lower end, and an upper end respectively, and which have sloping outward surfaces, so that when they are joined together with the coupling2, the annular projections16,16form an annular notch, which is in the shape of the annular notches

From the above description, it can be easily seen that the tube combination with the couplings according to the present invention is more economical to manufacture and safer to use than the prior one as described in the Background.