GB2505702A - Trepanning tool with retention mechanism - Google Patents

Abstract

The trepanning tool 102 includes a rotary body 103 having cutting elements 106 to cut, on rotation of the tool, a circular disc (354, Figure 3) from a workpiece 150. A disc retention mechanism 101 is disposed in the body to extend through a central hole 156 in the workpiece prior to commencement of cutting. A coolant distribution system is used to pressurise a coolant fluid between a first low pressure and a second high pressure at which the coolant is distributed to cool and/or lubricate the cutting elements. A chamber 109 with a piston 112 is actuated by the pressurised fluid to operate a retention leg 120 between a first disengaged position (Figure 1) when the fluid is at the first low pressure and a second engaged position (Figure 2) when the fluid is at the second high pressure. The retention leg is adapted to extend through the hole in the workpiece when the piston is in the disengaged position. When the piston is in the engaged position a disc cut from the work piece by the cutting elements is caught and retained by the leg (Figure 3).

Description

ATREPANNING TOOL WITH A RETENTION MECHANISM

[0001] This invention relates to a trepanning tool with a retention mechanism. In particular, the invention relates to retention mechanism for retention of a disc of material cut using the trepanning tool.

BACKGROUND

[0002] Trepanning tools are used to cut holes in sheet material. Sheet material may be relatively thick, of course, in the region of 100mm is not exceptional. Often the sheet material is part of a component which has an internal volume. Trepanning tools may comprise a series of teeth disposed around the circumference of tool, (although tools with one or two teeth are perfectly practical). The teeth are arranged to engage the material to cut it through its depth removing a disc of the material. The teeth may be cooled using a coolant that is supplied to the tool. Although somewhat unrelated to the present invention, trepanning tools are also known that comprise an electrolytic machining operation where an anode and cathode are used in combination to cut through the material, such methods are shown in US 3,909,388, for example.

[0003] Regardless of the approach used to cut a hole in the sheet material, all trepanning operations remove material in a circular slot and create a disc of the material in the centre of the hole. When trepanning expensive materials this disc can be valuable and may be recycled.

This is one reason why trepanning may chosen over other hole boring operations (which may result in material loss) although the primary reason it is used is usually merely the speed of completion of the operation (in that only the volume of the slot must be machined) and the reduced tool wear that results. Accordingly, it may be desirable to retain the disc once it has been machined, to prevent its falling into the volume of the component where it may be lost entirely. Other reasons also exist for why it may be desirable to retain the disc. For example, the disc may cause damage to the internal structure of the component, either in falling into the component when cut or through being left in the component during subsequent use of the component. The disc may affect the component's ability to perform its intended task. For example, where the component is intended to form a tank and the presence of the disc may alter the internal characteristics of the tank.

[0004] Retention of the disc is known in the prior art. GB 604,862 describes a trepanning tool furnished with a central rod mounted in the cutter body. The rod bears a pivotable arm which can turn into a position enabling the arm to be drawn into contact with the back surface of the material to be cut. In this position, the arm serves as a clamping jaw to clamp the disc of material after it is cut out. In use, the rod is manually inserted into a preliminary small hole through application of pressure to the rod. When the pressure is released from the rod, the device makes use of a compression spring which draws the arm onto the back surface of the material. The trepanning operation can then take place and the disc is retained. The device described in GB 604,862 does therefore show a retention mechanism for a trepanning tool.

However, the mechanism suffers in use because it requires manual pressure to be applied to the rod to move the retention means into position. Furthermore, the retention means cannot be disengaged and the trepanning operation must be completed before the tool can be removed.

Further still, the arm is pivoted into position through gravitational force on the unbalanced arm rendering the tool ineffective for use at certain angles. The off-centred weight of the retention arm may also have damaging effects on the balance of the tool in operation.

[0005] US 2,787,324 describes a wallboard cutter for use in making a hole in a dry wall after its installation over electrical fittings. Such a tool bears only a surface resemblance to a trepanning tool. The tool features a pair of separable cutters that are arranged on either side of the wall, i.e. one is disposed inside an electrical fitting that is installed behind the wall. The cutters are brought together via a scissor mechanism to remove a disc of material from the wall.

The disc is then retained in the space between the cutters and can be removed from the wall.

The cutter disposed on the opposing side of the sheet prior to the cutting operation makes it impossible to use the technique in many locations.

[0006] US 3,330,754 describes an electrochemical apparatus which uses a back-up member to support the workpiece and retain the disc that is being cut. The disc is shown to be retained/held by the back-up member using a magnet or a vacuum. US 3,330,754 therefore suffers from the same problems identified above in that the device requires a part, the back-up member in this case, to be disposed on the opposing side of the material. It also requires a flat surface and could not be employed to break through into a round bore.

[0007] It is therefore an object of this invention to provide a device that overcomes the problems identified hereinbefore, or at least mitigates their effects.

BRIEF SUMMARY OF THE DISCLOSURE

[0008] In accordance with the present invention there is provided a trepanning tool comprising: a body, for rotation about a rotation axis; cutting elements on said body, to cut a circular slot in a sheet workpiece of predetermined maximum thickness on rotation of the body about said axis; a disc retention mechanism, disposed in said body about said axis to extend through a central hole in said workpiece prior to commencement of cutting of the workpiece; and a coolant distribution system, to pressurise a coolant fluid for the cutting elements andlor workpiece between a first low pressure and a second high pressure at which said coolant is distributed to cool and/or lubricate the cutting element; wherein said disc retention mechanism comprises: a chamber in said body in fluid communication with said coolant distribution system; a piston in the chamber actuated by pressure of said fluid between a first, disengaged position when the fluid is at said first low pressure and a second, engaged position when the fluid is at said second high pressure; and a retention leg actuated by the piston and adapted to extend through the hole in said workpiece when the piston is in said disengaged position and, when the piston is in said engaged position, to catch and retain a disc of the workpiece when cut from the [0009] This has the advantage of providing a retention mechanism that is automatically engaged i.e. no manual pressure is required to drive the piston. Furthermore, the retention mechanism can be moved between the first and second configurations.

[0010] In a preferred embodiment said trepanning tool with a retention mechanism further comprises a lever mechanism for said operation of said moveable retention leg. Preferably, said lever mechanism is connectable between said cylinder and said piston, and further connectable to said retention leg. Furthermore, said lever mechanism preferably comprises a first pivot for connection said retention leg to said piston, and a connection rod connected between a midpoint on said retention leg and said cylinder. Further still, said connecting rod is optionally pivotally connected to said midpoint and said cylinder.

[0011] In another preferred embodiment, said trepanning tool with a retention mechanism further comprises at least one further moveable retention leg, wherein each of said retention legs are separated by an equal angle.

[0012] In still another preferred embodiment said tool comprises a wall and a mounting plate connectable thereto, said cylinder being disposed in said body about said mounting plate.

Preferably wherein said cylinder is connected to said mounting plate through a bearing [0013] In all of the preferred embodiments said piston preferably comprises a resilient member, said resilient member providing a force in a direction opposite to the force supplied by an increase in pressure between said first low pressure and said second high pressure.

[0014] In a further preferred embodiment, said tool comprises a fluid port for communication of said fluid in said body with said coolant system. Preferably, said tool further comprises a shank for connection of said tool to an external drive. Said fluid port may be disposed internally of said shank.

[0015] In another preferred embodiment, said tool comprises nozzles for said distribution of said coolant and/or lubricant to the cutting element. Where said tool further comprises a mounting plate, wherein said nozzles are preferably positionable in said mounting plate.

[0016] Furthermore, in accordance with this invention there is also provided a method of trepanning a material using a trepanning tool according to any of claims 1 to 9, wherein the material has a first side and a second side and a thickness therebetween, the method comprising the steps of: * drilling a pilot hole in said material; * positioning said trepanning tool, in a first configuration, on a first side of said material so that said retention mechanism extends through said pilot hole from said first side to said second side so that said retention legs are substantially beyond said second side; * pressurising said fluid to said second configuration so that said retention legs are in said second engaged position; * using said trepanning tool to cut a disc of said material; * removing said tool from said material, wherein said disc is retained by said retention mechanism; * depressurising said fluid to said first configuration so that said retention legs are in said first disengaged position and said disc is released.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which: Figure 1 shows a retention mechanism for a trepanning tool; Figure 2 shows a cross-sectional view of a retention mechanism for a trepanning tool in an engaged position; and Figure 3 shows a cross-sectional view of a retention mechanism for a trepanning tool in an engaged position.

DETAILED DESCRIPTION

[0018] Throughout the figures, corresponding reference numerals are used with a prefix relating to the figure number.

[0019] A retention mechanism 101 for a trepanning tool 102 according to the present invention is shown in Figure 1. The trepanning tool comprises one or more walls 103. The walls converge 104 on a central point where there is a shank 105 used for connection of the tool to the drive shaft of a tool drive (not shown). The converging walls 104 may be separate parts to the walls 103, being joined ata point therebetween, or alternatively, the walls and the converging walls may be integrally formed. The tool 102 has at least one cutting tooth 106 disposed at an opposite end of the walls 103 to the shank 105. The tool may have a plurality of cutting teeth disposed around the circumference of the walls.

[0020] The retention mechanism 101 is housed by the tool 102. Amounting plate 107 is fixed to the internal surfaces of the walls 103. The mounting plate 107 and the walls 103 form external boundaries to a volume or chamber 108 which is filled with a cooling fluid/lubricant for the tool 102 such as oil/water. The cooling fluid, or coolant, can be pressurised such that the pressure in the volume 108 is changeable. The coolant contained in the volume 108 is used to cool the trepanning tool 102 during operation and particularly to cool and lubricate the cutting tips 106 during cutting. Nozzles 158 may be disposed in the walls 103 of the trepanning tool 102 or in the mounting plate 107. Coolant under pressure in the volume 108 is fed through the holes onto the cutting tips to cool the tips during operation. The coolant is fed into the volume 108 via a port 159 in the shank 105. Itis appreciated that the port may be disposed in an alternate location and coolant may in addition or alteinatively be supplied to a sepalate cooling hose directing a flow of coolant at the tips 106.

[0021] A cylinder 109 is fixed onto the mounting plate 101. The cylinder 109 has a base 110 that forms the connection with the mounting plate 107. In the embodiment shown, the connection is made through bearings 111 fixed to the mounting plate, allowing the main body of the tool to rotate independently of the mechanism. The cylinder 109 houses a piston 112 moveable within the cylinder. The piston has a piston head 113 that substantially fits the internal walls 114 of the cylinder. By substantially fits, it is meant that there is a sufficient seal made between the piston head 113 and the internal walls 114 such that the coolant in the volume 108 does not fill the cylinder volume 115. Howevei, it is appreciated that some fluid may leak through this seal and enter the cylinder volume 115. Pores (not shown) are formed in the base 110 of the cylinder to permit exit of this fluid. Indeed, such pores are required to allow the passage of aft as the piston 112 moves within the cylinder 109.

[0022] The piston further complises a compression spring 116, or othei iesilient member, that provides a force to the relative underside of the piston head! working with a reference frame of the shank 105 being the top of the tool. The spring 116 returns the piston head to its uppermost position when there is reduced pressure on the piston head from above. The cylinder 109 has a top edge 117 which limits the extension of the piston head from the base 110. It is appreciated that the top 117 is not necessary to the function of this invention and extension of the piston may be limited by other means.

[0023] The piston further comprises a shaft 118 that extends below the piston head 113 and through the base 110. As shown in Figure 1, the shaft preferably extends below the culling teeth 106! relative to a direction taken fiom the shank 105 to the cutting teeth 106. At the base of the shaft 118, there is fixed a cross member 119 and at least one retention leg 120 pivotably fixed thereto. As mentioned above, the pivotal connection between the cross member 119 and the each retention leg 120, is provided at a pivot point, or first pivot, 121. Each retention leg has a second pivot 122 placed partway along the leg 120. There are no constraints over the displacement 123 of the further pivot from the first pivot. However, it will be appreciated below that as the second pivot moves closer to the first pivot, the force required to extend the legs becomes greater and as the second pivot moves away from the first pivot, the width of the retention mechanism in its extended position becomes wider, and this may limit effective use of the device. It is appreciated that selection of the displacement 123 is dependent on the operational circumstances for which the tool is intended and will be varied accordingly.

[0024] The second pivot 122 connects the retention leg 120 to a rod 124 which is also pivotally attached to the base 110. In Figure 1, the base 110 comprises a first 110', second 110" and third 110" component. It should be appreciated that these components can be integrally formed and it is their function, rather than form, that is important to the present invention. The precise make-up of these parts therefore serves only to provide a useful means of description. In this embodiment, the bearings 111, as described above, are connected between the mounting plate 107 and the second component 110" of the base. The rod 124 is pivotally connected to the third component 110". The first component 110' forms the base of the cylinder 109 and overlaps the bearings 111 such that the bearings are not exposed to the coolant in the volume 108. The mechanism created by the features described above, or otherwise, is best described by reference to the retention mechanism in use.

[0025] To cut a disc 354 (see Figure 3) from the material 350, a pilot hole 156 is first drilled in the material using a solid drill, or otherwise. The pilot hole must be large enough to accommodate the retention mechanism 101. Although referred to as a pilot hole, it is unlikely (although not necessarily so) that the pilot hole will actually serve to guide the tool 102, since this is most desirably mounted in a fixed machining centre, possibly as one turret ot a multi-axis multifunction tool (not shown or further described herein), and the workpiece 150 is likewise fixed in the machining centre with an appropriate mount or jig (not shown).

[0026] The tool is positioned so that the retention mechanism 101 extends through the hole 156 such thatthe retention legs are below underside surface 157 of the material 150. The coolant in the volume 108 is pressurised. This provides a torce to the upper surface of the piston head 113 which depresses the piston 112.

[0027] Referring to the pressurised system as shown in Figure 2 the piston 212 is depressed by the movement of the shaft 218 in a downward direction 251 which in turn causes the retention legs to pivot in an upward direction 252. This motion is caused by the lever mechanism created by the rod 224 connecting the base 210 to the retention leg 220. It should be noted that while the piston is depressed, the spring 216 is compressed.

[0028] Figure 2 therefore shows the retention mechanism 201, of Figure 1, in use. By use' it is meant that the trepanning tool is being used to cut a material 250 using the teeth 206. The retention mechanism is engaged with the application of coolant pressure before cutting and continues to remain engaged afterwards as is explained below.

[0029] When the retention mechanism is engaged, in use, the legs are raised under the material which is to be cut. The trepanning tool is then rotated and a cut 253 is made so that a disc shape piece 254 of the material 250 is cut away. As shown in Figure 3, when the disc 354 is cut from the material, retention legs catch the disc 354 and prevent it from falling below the material. This is particularly useful when the trepanning operation is used to cut a hole in a material which makes a component that has a cavity where retrieving a disc of material from that cavity after it has been machined would be problematic. After cutting through the material and freeing the disc 354, the trepanning tool stops rotating. Meanwhile, the retention mechanism 301 is still engaged. The tool is then removed from the material to a position where the coolant pressure can be decreased thereby removing the pressure on the piston head 313 such that the spring extends and the retention mechanism is disengaged and returns to the configuration shown in Figure 1. The disc 354 is then safely removed from the trepanning tool.

[0030] Figure 3 illustrates the selection of the displacement 323, equivalent to 123 above.

The displacement 323 between the first pivot 321 and the second pivot 322 has a direct relationship to the width 355 of the retention mechanism 355 which must be smaller than the width of the pilot hole 356.

[0031] Returning to Figure 1, it is also within the scope of the invention that the bearings 111 may be alternatively fixed to base 110. Furthermore, it is also within the scope of this invention to directly fix the base 110 to the mounting plate 107 without the interposed bearings 111 (this embodiment is not shown). However, the bearings 111 serve to permit rotation of the trepanning tool about the retention mechanism which remains relatively stationary and vice versa. This prevents problems that could be caused by heavier central sections 354 wearing the arms 120 when caught by the mechanism after dropping when cut. It is appreciated, however, that the friction across the bearings may cause the retention mechanism to rotate with the trepanning tool. Particularly where there are no bearings 111, it is important that the retention mechanism is balanced about its centreline to prevent vibration of the tool. However, even with bearings this is desirable since the mechanism is likely to rotate with the tool 102 until the central section 354 is cut and drops onto the arms 120. The retention mechanism is balanced by having appropriately distributed retention legs. In the embodiment shown in Figure 1, there are three retention legs spaced 120° from each other in a plane perpendicular to the shaft. It is within the scope of the invention to have less or more legs. For example, the retention mechanism could have four legs spaced 90° from each other to achieve a balanced system.

[0032] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

(0033] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process SO disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

(0034] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.