TOOL AND METHOD FOR FORMING A THREAD

[001] The present invention relates to a tool and a method for forming a thread on a surface defining a bore, such as the internal surface of a tube.

[002] There are a number of known processes for forming a thread on the internal surface of a tube, for example, tapping and thread rolling. [003] Tapping involves the use of a suitable tap to cut the thread into the material of the tube by rotating and displacing the cutting surface of the tap relative to the tube. A tap can also be used to roll a thread in a suitably malleable material by rotating and displacing the tap relative to the tube. In less malleable materials, the tube may be treated (for example by heating) to make the internal surface thereof malleable, prior to rolling the thread. [004] In both cases the tap is driven into and along the tube by a driving shaft in order to form the thread. To enable the tap to form a thread over the required length of tube, the driving shaft must be at least as long as the length of tube to threaded. However, accurate tapping can only be achieved with relatively short drive shafts, which limits the length of tube over which a continuous thread can be formed using previously known techniques. [005] Moreover, swarf created when the thread is cut tends to clog the tap, limiting the length of tube which can be continuously threaded still further. Even if the swarf is channelled downstream of the tap and away from the cutting edge, it will then interfere with operation of the driving shaft, thereby limiting the length of tube which can be continuously threaded.

[006] In practice, the longest continuous internal thread achievable with previously known methods is in the region of 150 mm. [007] There are many applications in which an internally

threaded tube or bore, with a continuous thread length of greater than 150 mm is desirable. For example, such tubes are particularly useful where a drive mechanism is needed in a longitudinally extending, transversely constrained space. [008] It is an object of the present invention to overcome the shortcomings of the prior art.

[009] According to a first aspect of the present invention there is provided a tool for forming a thread on a surface defining a hole or bore, the tool comprising: - a thread forming portion comprising one or more thread forming ridges; and an elongate portion for pulling the thread forming portion through the bore; wherein the thread forming portion is provided rearwards of the elongate portion in a thread forming direction of travel through the bore.

[0010] That is to say, the one or more thread forming ridges are positioned or orientated to form a thread when the thread forming portion follows the elongate portion through the bore.

[0011] Thus, the tool is designed to be pulled rather than pushed through the bore to be threaded. Since the tool is drawn through the bore by tensile forces in the elongate portion (rather than compression forces, as is the case with the prior art) , the elongate portion can be made significantly longer than the shafts of prior art devices without sacrificing control over the thread forming portion. Accordingly, continuous threads can be formed over significantly greater lengths than was possible with prior art devices.

[0012] Furthermore, since the tool is drawn through the bore by tensile forces in the elongate portion, the elongate portion (member) need not be made as rigid as the shafts used for prior art devices. For example, flexible tubing could be used. In particular, it is possible for the

elongate portion to be made hollow without limiting the length of the shaft. This allows for cooling and lubricating fluids to be channeled through the elongate portion, if required. [0013] The terms "pulling" and "drawing" as used herein refer to a relative movement between the surface to be threaded and the tool. Thus, the claimed invention encompasses a situation where the surface to be threaded is kept still whilst the tool is drawn through the bore, and also the situation where the tool is kept still, and the surface ^, to be threaded is moved, so as to achieve the same relative movement that would be achieved had the tool been pulled or drawn through the bore. [0014] The tool may comprise one or more channels for channeling swarf created in forming the thread away from the thread forming ridges.

[0015] Since the thread forming portion is located downstream of the elongate portion, channeling the swarf away from the thread forming ridges "also channels it away from the elongate portion, so that it is prevented from interfering with or obstructing the passage of the elongate portion through the bore.

[0016] Moreover, the tool produces a continuous spiral of swarf, which is left behind the tool as it progresses through the bore. As a result, it is not necessary to stop and reverse the tool in order to "break" the swarf. [0017] The tool may comprise means for transporting cooling and/or lubricating fluids through to or towards the one or more thread forming ridges. [0018] This prevents heat generated in forming the thread from warping or otherwise damaging the surface to be threaded or the tool itself.

[0019] The elongate portion may comprise a tube defining a hollow interior. [0020] In use, the elongate portion may define a conduit

together with the surface defining the bore for transporting cooling and/or lubricating fluids through the hollow interior of the tube to or towards the one or more thread forming ridges . [0021] The conduit may be defined by:- a reduced diameter portion of the tube adjacent the thread forming portion of the tool, which, in use, creates space between the external surface of the tube and the ^• surface defining the bore; and one or more openings in the reduced diameter portion of the tube, for, in use, allowing fluid to flow from the hollow interior of the tube into said space. [0022] The elongate portion may be longer than a bore to be threaded. [0023] This ensures that part of the elongate portion extends out of the bore to be threaded, so that it can be drawn through the bore.

[0024] The tool may be for forming a continuous thread over a length of tube in the range 300 to 1100 mm. [0025] The thread forming ridges may be thread cutting ridges for cutting a thread, or thread rolling ridges for rolling a thread.

[0026] According to a second aspect of the present invention there is provided a method for forming a thread on a surface defining a bore, the method comprising the steps of:- rotating a thread forming member; and pulling the thread forming member through the bore. [0027] Since the thread forming member (portion) is pulled rather than pushed through the bore to be threaded, continuous threads can be formed over significantly greater lengths than was possible with previously known methods. [0028] The method may further comprise providing lubricant and/or cooling fluids to thread forming ridge (s) of the thread forming member. [0029] The method may further comprise part-threading a

portion of the tube before rotating and pulling the thread forming member through the bore.

[0030] An embodiment of the present invention will now be described with reference to ^" the accompanying diagrams in which: -

[0031] Figure 1 is a cross-sectional side view of a tapping tool embodying the present .invention;

[0032] Figure 2 is a perspective view of a threaded tube made using the method of the present invention; and [0033] Figure 3 is a simplified perspective view of a tapping head of a tapping tool embodying the present invention.

[0034] Figure 1 illustrates a tapping tool (tap) 10 which comprises a shaft 14 and a tapping head 12. [0035] The shaft 14 is formed as a tube with a hollow interior 26. Only a portion of the shaft 14 is illustrated in Figure 1. However, it is to be realised that the shaft may be made as long as required, and should be longer than the tube to be machined. [0036] With reference to Figures 1 and 3, the head 12 has three spiral shaped (helical) cutting surfaces 16, 17, 18 which extend from part way along the longitudinal dimension of the head to an end 36 thereof, and are disposed at regular intervals about a rotational axis 20. The cutting surface 17 is not shown in Figure 1. The three cutting surfaces 16, 17, 18 are separated by three spiral shaped (helical) flutes, two of which (22, 24) can be seen in Figure 3. As shown in Figure 3, the three cutting surfaces 16, 17, 18 each comprise a series of teeth 300 which define a series of cutting edges or ridges which extend across the respective cutting surfaces following a helical path around the tapping head. To the right of the cutting surfaces as viewed in Figure 1, the head 12 is formed as a cylindrical projection 13, which fits into the hollow interior 26 of the shaft 14 to secure the head to the shaft in such a way that

the teeth 300 of the cutting surfaces are orientated to cut a thread in the internal surface of a bore when the tapping tool is drawn through the bore in the direction of arrow 46. For clarity, only part of the shaft 14 is shown in Figure 3. [0037] The shaft 14 includes a region 28 of reduced diameter at an end 35 of the shaft. The projection 13 of the head 12 is formed to fit tightly and securely within the region 28 of the shaft 14. Additional bonding means may be provided for securing the projection 13 in the shaft 14. [0038] The region 28 is longer than the projection 13 so that when the projection is fully located within the shaft 14, the region 28 extends beyond the end of the projection 14. Two openings 30 and 32 are provided in the wall of the shaft 14 in the region 28 beyond the end of the projection 13. In practice, more than two openings may be provided.

Alternatively, only one opening may be provided.

[0039] In use, the tapping tool 10 is fed into a tube to be threaded so that an end 34 of the shaft 14 opposite the head

12 extends out of the tube and the ends of the cutting surfaces 16, 17, 18 abut an end of the tube.

[0040] The end of the tube to be threaded may be part threaded using previously known methods to allow the tapping tool 10 to enter the tube more easily. [0041] A driving machine (not shown) then engages with the end 34 of the shaft and rotates the shaft 14 about the axis of rotation 20, causing the teeth 300 of the cutting surfaces 16, 17, 18 to cut into an inner surface of the tube. Simultaneously, the tapping tool 10 is drawn in the direction of arrow 46 by pulling on the exposed section of the shaft 14 while the tube is kept stationary.

[0042] The combination of the movement of the tapping tool 10 in the direction of arrow 46 and the rotation of the tapping tool 10 about axis 20 causes the teeth 300 of the cutting surfaces 16 17, 18 to form a thread in the inner surface of the tube. This process is continued until a

thread has been formed over the required length of the inner surface of the tube.

[0043] The cutting process produces heat. To prevent this heat from warping the tube or the tap 10, cooling and/or lubricant fluids are introduced under pressure into the hollow interior 26 of the shaft 14. The fluids exit the interior 26 through the openings 30 and 32 in the shaft 14. The area of reduced diameter 28 forms a conduit between the shaft 14 and the tube. The fluids are transported along this conduit towards the cutting surfaces 16, 17, 18 to cool and lubricate them on contact.

[0044] The swarf cut by the edges 16 and 18 is transported away from the head by the helical flutes 22 and 24. [0045] Figure 2 illustrates ^' a tube 60 having an inner surface 62 with a thread 64 formed therein by use of the tap 10 illustrated in Figure 1. " The thread 64 extends along the entire length L of the tube 60.

[0046] Although the tapping head described above comprises thread cutting surfaces which each have a series of teeth for cutting a thread, the thread forming ridges of the present invention may take any suitable form for forming a thread. For example, the thread forming surfaces may each comprise a single ridge which extends around and along the tapping head in a helical manner for cutting or rolling a thread. Moreover, although the embodiment described above has three thread forming surfaces, embodiments of the present invention may alternatively have one, two or more than three thread forming surfaces.

[0047] Although the present invention has been described above in terms of cutting a thread, the present invention could also be used for rolling a thread on the internal surface of a tube. In this case the helical flutes for transporting swarf away from the tapping tool will not be necessary. [0048] In the above description, the tube is held

stationary, while the tapping tool is rotated and moved along the length of the tube. However, it will be appreciated that it is the relative movement of the tube and the tapping tool which is important. Accordingly, the tapping tool may be held still whilst the tube is rotated and moved linearly in a direction opposite to the direction of the arrow 46 in Figure 1; the tapping tool may be rotated whilst the tube is moved linearly in a direction opposite to the direction of the arrow 46 in Figure 1; or the tube may be rotated whilst the tapping tool is drawn in the direction of the arrow 46 in Figure 1.

[0049] With the present invention, continuous internal threads over the full length of a tube have been successfully formed for tubes of lengths between 300 and 1000mm. However, continuous internal threads for longer or shorter tube lengths are also possible.

[0050] Further, continuous internal threads have been successfully formed for tubes made of ferrous steel, stainless steel, aluminium alloy, and various plastics. [0051] Although the above description refers to forming a thread on the internal surface of a bore, it will be appreciated that the present invention applies equally to providing a thread to any surface defining a hole or a bore. [0052] The tube can be produced with single or multi-start threads in either clockwise or counter-clockwise directions.