Hand held joining apparatus

Abstract

A force generating apparatus includes a housing, a piston movably mounted in a cavity and a punch and die mounted in the housing. The punch and die are normally spaced apart to receive two overlapping sheets of metal. The piston moves a wedge against the punch toward the die in order to clinch two overlapping sheets together.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to metal working apparatuses and more particularly to hand held devices utilizing a mechanical multiplication scheme with a low pressure fluid.

BACKGROUND AND SUMMARY OF THE INVENTION

[0002] There is often a need to join two or more pieces of sheet material to form various assemblies and subassemblies. There are several ways of accomplishing this. One such way is to deform the sheet material to form an interlocking and leakproof clinched joint.

[0003] In clinched joints, several pieces of sheet material are plastically deformed in such a manner that they are locked or pierced together. Depending on the thickness, strength, and/or the number of pieces of material to be joined, a great amount of force is required to accomplish this plastic deformation.

[0004] An apparatus and method for accomplishing a clinched joint of sheet material are disclosed in commonly assigned U.S. Pat. Nos. 5,027,503, 4,910,853, 4,757,609, the disclosures of which are expressly incorporated herein by reference. As is disclosed in these patents, the sheets of material to be joined are placed between complementary die and punch members. A suitable press is then activated to provide the force and displacement necessary to deform the material between the die members thereby joining the sheets of material together.

[0005] In the embodiments disclosed in the above U.S. patents, the dies are generally attached to relatively large presses thus requiring the sheets to be joined to be manipulated with respect to the press. In contrast, portable spot welding devices have been in existence for many years. These smaller devices allow for the joining tool to be manipulated with respect to the workpiece thereby making it easier to work with large workpieces. Smaller portable tools are available which can provide the necessary clamping force to join the sheets and which allow for manipulation of the joining tool with respect to the workpiece and thus allow for easier operations with larger workpieces. One such tool is a riveting tool shown in U.S. Pat. No. 2,313,843. This tool uses pneumatic pressure in a cavity to move a pair of pistons arranged in tandem to create a portable rivetor. The pistons move linearly in the cavity to urge a reciprocating toggle mechanism to move a punch in a bore that is substantially perpendicular to the axis of the cavity to urge a rivet toward an anvil in order to rivet the workpiece. While the tool is designed to be portable, it is bulky and the level of force that is generated by this tool is limited by the size of the cavity that can be incorporated into the tool while maintaining its portability.

[0006] Another such tool is disclosed in commonly assigned U.S. Pat. No. 4,878,284, the disclosure of which is expressly incorporated by reference herein. This tool incorporates a pneumatic or hydraulic cylinder to provide the force and displacement necessary for sheet material joining and clamping. Unfortunately, the level of force generated by this device is limited by the size of the cylinder which can be incorporated into the tool while still maintaining the compact, light weight nature of a hand held portable tool.

[0007] Still another such tool is described in U.S. Pat. No. 5,431,089 and also owned by the assignee of the present application. The device has a body and an anvil which is connected to the body. The body has an actuating chamber with a generally arcuate surface and a flat surface against which a ram is contained. The ram is made of spring sheet steel. In a relaxed state, the ram has a generally arcuate shape corresponding to the arcuate surface in the chamber with a forward tang that engages the punch. Air pressure is used to bear against the ram causing the ram to deflect and move the punch longitudinally toward the anvil. This provides a “toggle-like” mechanical advantage which creates a force multiplying effect.

[0008] This device is limited by the size and shape of the actuating chamber and the size of the ram. Additionally, the device is complex and limited by the size of the cavity which can be encapsulated into the hand held tool while maintaining its compact and lightweight features.

[0009] Thus, there is a need for a hand held device that is simple and inexpensive and yet provides a force multiplying effect that is not limited by the size of the actuating chamber to provide the displacement necessary in order to produce the force necessary to cold forming two or more sheets of metal and does not require a force intensifier as is common in the prior art.

[0010] In accordance with the present invention, a joining apparatus provides an inexpensive and simple hand held device that deforms two or more overlapping workpieces with a low pressure fluid source in combination with a wedge shaped force multiplier.

[0011] Another aspect of the present invention is directed to an apparatus adapted for cold forming or clinch joining at least two overlapping sheets of metal wherein the apparatus has a housing, a punch and a die member aligned on a central axis and normally spaced apart a sufficient distance to receive the overlapping sheets therebetween.

[0012] In a further aspect of the present invention, the apparatus includes a piston movably mounted in the housing and a wedge between the piston and the punch. The wedge urges the punch along the central axis toward the die and against the two overlapping sheets of metal whereby the sheets are cold formed.

[0013] The present invention apparatus is advantageous over conventional devices since the present invention provides a hand held device that has an inclined force multiplication device acting on the end of a punch to cold form sheets of metal that is simple and inexpensive to make and does not require a force intensifier. Additionally the device is compact, rugged, light weight and easy to operate.

[0014] These and other features and advantages of the present invention will become apparent from the subsequent description and claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0016] FIG. 1 is a side view with a partial cross section of the apparatus according to the present invention with the die spaced apart from the punch;

[0017] FIG. 2 is a side view with a partial cross section of the apparatus according to the present invention with the die against the punch;

[0018] FIG. 3 is a cross-sectional view of the piston along line 3-3 in FIG. 1;

[0019] FIG. 4 is a cross-sectional view of a wedge along line 4-4 in FIG. 2;

[0020] FIG. 5 is a cross-sectional view of a spacer along line 5-5 in FIG. 2; and

[0021] FIG. 6 is an exploded view of the top of the piston, spacer, wedge, and the rod and shaft of the hand apparatus according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] The present invention is described for illustrative purposes embodied in a pneumatically actuated hand held portable sheet material forming tool. It will be appreciated, however, that the principles of the present invention are readily adaptable to a number of manufacturing processes which involve force generation or joining including clinching, clamping, piercing and holding.

[0023] FIGS. 1-6 show the preferred embodiments of a sheet material joining apparatus or force generating device 100 of the present invention. Apparatus or device 100 includes a body 10, a punch member 24, a piston 40, an inclined force multiplication member 50 and a jaw 80.

[0024] Although only two pieces of sheet metal are shown in FIGS. 1 and 2 to be clinched, it is to be understood that more than two pieces may be clinched or joined depending on sheet thickness and/or sheet material properties. The sheets may be made of metal or polymeric material. The joint so formed, and the method and apparatus for forming it, are shown and described in the herein-above referenced U.S. Pat. Nos. 4,459,735 and 4,757,609, the disclosures of both of which are expressly incorporated herein by reference.

[0025] Body or housing 10 has a contoured surface 12, an actuating chamber 14, a first central bore 16 and a second central bore 18. Contoured surface 12 defines a hand grip and is mounted on a cover plate 13. Cover plate 13 is conventionally fastened (not shown) to the body 10. A seal (not shown) is sandwiched between cover 13 and body 10 to enclose and seal pneumatic pressure in chamber 14. Actuating chamber 14 has a generally cylindrical shape with an oval cross-section for a purpose to be described later on. First central bore 16 is aligned with second central bore 18 and defines a central axis 11. First central bore 16 has an open end and a first closed end 17. Second central bore 18 also has an open end and a closed end 19. First closed end 17 and second closed end 19 are adjacent but spaced apart from each other. A passage 15 extends axially along central axis 11 to communicate with the first and second bores 16, 18 respectively. Body 10 is preferably made of a light weight material such as aluminum or other suitable material.

[0026] A punch member 24 is disposed in first central bore 16. Punch member 24 has an axially extending shaft 22, a radial groove 23 on its outer surface with an O-ring seal 27. O-ring seal 27 is made of a suitable polymeric material such as nitrile and is disposed in the groove 23 to sealingly engage shaft 22 with inner radial surface of first bore 16 and to seal pneumatic pressure in body 10. One end of shaft 22 has a punch die and the other end has an inclined end 26 with a threaded bore 28. End 26 will be described in more detail later on.

[0027] Rod 34 is disposed in passageway 15. Rod 34 has a threaded end 35 which engages threaded bore 28 in punch member 24. Rod 34 also has an opposite threaded end 37 which extends axially into second bore 18. Spring 32 is placed in second bore 18 and surrounds rod 34 adjacent to threaded end 37. Spring 32 is preferably a coil spring that abuts against closed end 19 of second bore 18. Spring 32 is retained in second bore 18 by a washer 36 with a hole. Threaded end 37 extends through the hole in washer 36 and is engaged by threaded nut 38. Spring 32 urges punch member 24 towards first closed end 17 in bore 16. The biasing force of spring 32 is adjusted by the diameter of spring 32, coil spring thickness and number of coils in spring 32 and by advancing threaded nut 38 on threaded end 37 axially toward or away from second closed end 19 of bore 18 as is well known in the prior art. A circular groove is formed in body 10 near passageway 15 and an O-ring seal is retained therein. The O-ring seal abuts against a cylindrical outer portion of rod 34 which is between ends 35, 37 respectively to sealingly engage rod 34 between first bore 16 and second bore 18 and to seal pneumatic pressure in body 10.

[0028] Piston 40 is disposed in actuating chamber 14. Chamber 14 is located adjacent to but spaced away from bores 16, 18 respectively. Piston 40 has a cylindrical shape with an oval cross-section which generally corresponds to the shape of chamber 14 so that piston 40 travels axially along the axis of chamber 14 from one end adjacent to cover plate 13 to a second end adjacent but spaced away from bores 16, 18 respectively. Piston 40 has an outer rim with a medial annular groove 42. Elastomeric seal 44, which is made of a suitable polymeric material such as nitrile, is retained in groove 42 to sealingly engage inner radial side walls of chamber 14 and to seal pneumatic pressure therein. Piston 40 has a longitudinal slot 46 extending radially along top 43 of piston 40. Slot 46 has an undercut 47 formed in piston 40 that connects with cavity 48 that is formed on one end of slot 46. Piston 40 is made of aluminum or other suitable material.

[0029] Inclined force multiplication member 50 is inserted into slot 46 in piston 40. Member 50 includes a wedge 51, a spacer 60 and half spacer 68. Wedge 51 has a top planar portion, a pair of edges and a bottom portion. The top planar portion has a first inclined surface 52 and an opposite second inclined surface 54 as best shown in FIGS. 1, 2 and 6. Bottom portion has a locking member 57 defining a T-shaped configuration which is inserted into slot 46 in the piston 40. Wedge 51 is inserted into cavity 48 and then is slidingly positioned in slot 46 so that member 57 lockingly engages undercut 47 as best shown in FIG. 4. Wedge 51 thus can slide in slot 46 axially but is prevented from being disengaged from piston 40 because the extending arms of locking member 57 are captured in undercut 47 in slot 46. Preferably, there are three wedges 51 inserted into slot 46 however, optionally there may be between one to five wedges 51 inserted therein. The angle β between a vertical axis and the inclined surfaces 52, 54 respectively is 5 degrees and may be between 3 to 7 degrees and optionally between 2 to 10 degrees depending on the length of the forming tool 100, the force required to clinch the sheets and the number of wedges and spacers used. Returning back to FIG. 1, wedge member 51 extends axially from the top of piston 40 into cavity 20 formed in first bore 16 between end 26 of shaft 22 and closed end 17 of bore 16. Wedge 51 has a notch 56 in the top portion to permit wedge 51 to slide past rod 34 and slidingly engage spacer 60 as wedge 51 is moved into cavity 20 by piston 40 as will be discussed later on.

[0030] As is best shown in FIGS. 5 and 6, spacer 60 has a bore 66 and is formed in a wedge shape. Spacer 60 has a first slanted surface 62 on one side and a second slanted surface 64 on the opposite side. The angle β′ between a vertical axis and surfaces 62, 64 respectively is 5 degrees and may be between 3 to 7 degrees and optionally may be between 2 to 10 degrees depending on the length of the forming tool 100, the force required to clinch the sheets and the number of wedges and spacers used. Similarly, the angle β″ from vertical axis for inclined end 26 is 5 degrees and may be between 3 to 7 degrees and optionally between 2 to 10 degrees depending on the length of the forming tool 100, the force required to clinch the sheets and the number of wedges and spacers used.

[0031] Spacer 60 is disposed in cavity 20 and rod 34 extends through bore 66 to capture spacer 60 in cavity 20. The wedge shape of spacer 60 slidingly engages the inclined surface of wedge 51 to move shaft 22 axially along central axis 11 towards jaw 80. Preferably, multiplication member 50 is lubricated with a suitable lubricating fluid such as grease or oil to reduce friction, or optionally, inclined surfaces 26, 52, 54 respectively and slanted surfaces 62, 64 respectively are chrome plated or coated with a layer of lubricious material such as polytetrafluoride or PTFE. Preferably, there are two spacers 60 and a half spacer 68 in cavity 20. Optionally, the number of spacers 60 may be varied between one to four or alternatively, spacer 60 may be eliminated and only half spacer 68 inserted into cavity 20 where only one wedge 51 is used. Those skilled in the art will recognize that the angle of the surfaces 62, 64 respectively may be varied to increase or decrease the force multiplication and travel of the device as required.

[0032] Half spacer 68 has only one inclined surface 67 to engage an inclined surface of wedge 51. The other surface of spacer 68 abuts the closed end of bore 16. Half spacer 68 also has a bore 69 to permit rod 34 to capture it in bore 16. The angle β′″ from vertical of the inclined surface 67 is 5 degrees and may be between 3 to 7 degrees and optionally between 2 to 10 degrees depending on the length of the total 100, the force required to clinch the sheets and the number of wedges and spacers used.

[0033] Jaw 80 is secured to body 10 by a dowel and screw as is well known in the art. Jaw 80 has a die member 86. As described in greater detail in the aforementioned U.S. patents, punch member 24 and die 86 are operable to plastically deform and thereby clinch a number of sheets of material upon translation movement of punch member 24 relatively towards die member 86. Preferably, punch member 24, die member, and multiplication member 50 are made of hardened steel or any other suitable material.

[0034] A 4-way power valve 90 is disposed on contoured surface 12. Valve 90 receives air from fitting 98 and it controls whether air is to be supplied to chamber 14 or optionally cavity 20. Valve 90 communicates air supplied from a hose 97 and fitting 98 through bores 92, 94, 96 respectively to chamber 14 and alternatively supplies air through a bore (not shown) to cavity 20. As noted, when air is supplied to chamber 16, piston 40 moves upwardly toward bores 16, 18 respectively and wedge 51 slidingly engages spacer 60 and/or half spacer 68 to urge shaft 22 toward the jaw 80. Conversely, when air is supplied to cavity 20, wedge 51 slidingly engages spacer 60 and/or half spacer 68 and moves toward cover plate 13. Spring 32 biases shaft 22 to move away from jaw 80 as piston 40 moves downwardly toward cover plate 13. Compressed air flows from a source (not shown) and into hose 97 and fitting 98 and is supplied through a filter-regulator-lubricator (not shown) to pressurize trigger valve 90 on contoured surface 12 to cause valve 90 to pressurize chamber 14.

[0035] By way of a nonlimiting example, the force generation attributes of device 100 will now be described. The force generated by a wedge moving perpendicular to the axis of a punch is described by the following formula which is disclosed in page 109 of Machinery's Handbook (24th ed.) and is modified herein for the sake of clarity.

[0036] Q=½ p cot β

[0037] where: Q=mechanical force

[0038] p=pneumatic force on the piston (pressure×area)

[0039] β=is the half angle of inclination of the inclined surface relative to the axis of travel of the piston

[0040] With air pressure of 80 psi and piston surface area of 18.9 sq. inches, and β=5 degrees,

[0041] Q=½ (80×18.9) (cot 5°)=½ (1512) (11.43003)

[0042] Q=8641 pounds of force

[0043] Q=4.32 tons

[0044] Thus, 80 psi of pressure on the piston generates 4.32 tons of force generation between the punch and die to form clinched metal sheets.

[0045] The operation of force generating device 100 will now be described in detail with reference to FIGS. 1 and 2. Cold forming apparatus 100 is actuated by depressing valve 90 on hand grip 12. Preferably, air pressure of approximately 80 to 100 psig flows from hose 97, through fitting 98, into valve 90 through bores 92, 94 and 96 and into actuating chamber 14. Air pressure bears on bottom surface 41 of piston 40 causing piston 40 to move toward central axis 11. This causes inclined surfaces 52, 54 respectively of wedge 51 to slidingly engage slanted surfaces 62, 64 respectively of spacers 60 and inclined surface 67 on half spacer 68 and inclined end 26 of shaft 22. Thus, shaft 22 overcomes the biasing force of spring 32 and translates longitudinally along central axis 11 towards die member 86. Sheet materials A, B are inserted between die 86 and punch 24 before actuation of apparatus 100. When the apparatus is actuated, sheets A, B are plastically deformed or clinched as described in the aforementioned patents.

[0046] Since piston 40 has a relatively large surface area on its bottom 41, a large upward force is generated by the air pressure acting on this surface area. This force is exerted against wedge 51, spacer 60, half spacer 68 and inclined end 26 of shaft 22. The upward force overcomes the biasing force of spring 32 acting on shaft 22 and causes wedge 51 to slide on slanted surfaces 62, 64 respectively of spacer 60, the slanted surface of half spacer 68 and inclined end 26 of shaft 22. Wedge 51, spacers 60, half spacer 68 and inclined end 26 cause the upward force of the air pressure acting on piston 40 to be translated into longitudinal movement of shaft 22. Additionally, the force acting on piston 40 is multiplied as the movement of wedges 51 against spacer 60, half spacer 68 and end 26 acting on their respective inclined/slanted surfaces as described earlier. This results in force multiplication that is sufficient to permit clinching of sheet materials A, B respectively when shaft 22 axially translates punch 24 to engage die 86.

[0047] After sheet materials A, B respectively are clinched, pressure in chamber 14 is released by pressing the trigger in one position which causes valve 90 to evacuate chamber 14 through passages (not shown) to a muffler (not shown). As best shown in FIG. 2, when the pressure is released from chamber 14, piston 40 moves downward so that bottom surface 41 moves toward cover plate 13 in body 10. Optionally, to assist the downward movement of piston 40 in chamber 14, air is introduced into cavity 20 by depressing the trigger in another position so that the air bears on top 43 of piston 40 causing wedge 51 to move away from central axis 11 and slide on the inclined surface of end 26 of shaft 22, inclined surface 67 of half spacer 68, and slanted surfaces 62, 64 respectively of spacer 60. Spring 32 assists in biasing punch member 24 away from die 86. This permits sheet materials A, B to be removed from apparatus 100. It should be appreciated that die 86 may be replaced with clamping jaws or other tooling devices to accomplish a variety of tasks. It is also possible to mount a number of force generating units equipped with appropriate tools to create a work fixture into which a workpiece may be inserted and a number of operations performed simultaneously.

[0048] Those skilled in the art will recognize that while the device was described with pneumatic pressure, hydraulic pressure, an electric motor may alternately be employed to move piston 40 or any another suitable mechanism in the chamber 14.

[0049] While it is apparent that the preferred embodiment of the invention disclosed is well calculated to provide the advantages and features above stated, it will be appreciated that the invention is susceptible to modification, variation, and change without departing from the proper scope or fair meaning of the subjoined claims. For example, the apparatus may be stationarily mounted to a factory floor or fixture. The apparatus may also be attached to an articulating robotic arm. Furthermore, extra linkages or cams can couple the wedges to the joining dies. Pierced or riveted joints can also be performed with the present apparatus. Other materials and dimensions can be substituted for those disclosed. It is intended by the following claims to cover these and any other departures from the disclosed embodiments which fall within the true spirit of this invention.

Claims

1. A workpiece joining apparatus comprising: a housing having a central axis; a punch disposed on the central axis; a die aligned with the punch; a piston movably mounted in the housing; and a wedge located between the piston and the punch, the wedge being operable by the movement of the piston to urge the punch along the central axis relative to the die.

2. The apparatus as claimed in claim 1 wherein the housing has a bore and a cavity, the punch is disposed in the bore, the piston is disposed in the cavity, the cavity has a piston axis defined by the direction of travel of the piston and the piston axis is substantially perpendicular to the central axis.

3. The apparatus as claimed in claim 2 wherein the bore has an open end and an opposite closed end, the closed end has an inclined surface to slidingly engage the wedge as the wedge moves into the bore.

4. The apparatus as claimed in claim 3 further comprising: a spacer adjacent the wedge, the spacer having at least one slanted surface, and the wedge having an inclined surface to slidingly engage the slanted surface of the spacer.

5. The apparatus as claimed in claim 1 further comprising a spring biasing the punch away from the die.

6. The apparatus as claimed in claim 1 wherein the punch and the die operably create a workpiece joint.

7. The apparatus as claimed in claim 1 wherein the wedge has at least one inclined surface.

8. The apparatus as claimed in claim 2 wherein the piston is pneumatically moved in the cavity in a linear direction by air pressure.

9. The apparatus as claimed in claim 1 wherein the elongated orientation of the wedge is substantially perpendicular to the central axis.

10. A force generating device comprising: a workpiece joining member; a first member coupled to the workpiece joining member, the first member having an inclined surface, the first member being moveable in a first linear direction; a second member adjacent the first member, the second member having an inclined surface to engage the inclined surface of the first member; and a piston adjacent to the first member, the piston operably advancing in a second linear direction which is substantially perpendicular to the first direction, so that the piston urges the second member to slidingly engage the first member to generate force which is transmitted to the workpiece joining member.

11. The device as claimed in claim 10 wherein the workpiece joining member is disposed on a central axis, the workpiece joining member has a die and a punch in a normally spaced apart condition, the punch is urged toward the die along the central axis when the force is transmitted to the workpiece joining member.

12. The device as claimed in claim 10 further comprising: a third member adjacent the second member, the third member has at least one slanted surface to engage the inclined surface of the second member.

13. The device as claimed in claim 12 wherein the biasing member is a spring.

14. The device as claimed in claim 11 further comprising a biasing member and wherein the punch is biased away from the die by the biasing member.

15. A hand held apparatus comprising: a housing having a cavity; a punch and die coupled to the housing, the punch and die being substantially aligned on a central axis; a piston movably mounted in the cavity; a wedge drivingly located substantially between the piston and the punch, the wedge operably advancing the punch along the central axis toward the die; at least two overlapping workpiece sheets disposed between the punch and the die; and a clinch joint formed between the overlapping sheets when the piston moves substantially perpendicular to the punch thereby urging the punch toward the die and engaging the overlapping sheets.

16. The apparatus as claimed in claim 15 wherein the wedge is connected to the piston.

17. The apparatus as claimed in claim 15 wherein the opposite end of said punch has an inclined surface.

18. The apparatus as claimed in claim 17 wherein the wedge has an inclined surface, the inclined surface slidingly engaging the inclined surface of the punch.

19. The apparatus as claimed in claim 18 further comprising: a biasing member connected to the punch and urging the punch away from the die.

20. A method of workpiece joining using a punch, piston, a first inclined member, and a second inclined member, the method comprising: (a) moving the piston in a first direction; (b) moving the first inclined member in the first direction in response to step (a); (c) moving the second inclined member in a second direction, substantially perpendicular to the first direction, in response to step (b); and (d) advancing the punch substantially in the second direction.

21. The method as claimed in claim 20 wherein the axis of the cavity is substantially perpendicular to the central axis of the bore.

22. The method as claimed in claim 21 wherein the bore has an open end and an opposite closed end, the closed end has an inclined surface to slidingly engage the wedge as the wedge moves radially into the bore.

23. The method as claimed in claim 22 further comprising: biasing the punch away from the die.

24. The method as claimed in claim 22 wherein the moving step includes forming a force multiplier when the wedge slides against the punch.

25. The method as claimed in claim 23 wherein the biasing step includes a spring and a rod, the rod is adjustably mounted to the punch, the spring is disposed in a second bore, the second bore is adjacent but spaced away from the bore, the spring is adjustable in the second bore.

26. The method as claimed in claim 23 further comprising: placing at least two overlapping sheets between the punch and a die.

27. The method as claimed in claim 20 further comprising: forming a clinch joint between the at least two overlapping workpiece sheets.

28. The method as claimed in claim 23 wherein the wedge has an elongated portion, the elongated portion has an inclined surface, the punch has an inclined surface, the inclined surface of the wedge slidingly engages the inclined surface of the punch.

29. The method as claimed in claim 20 further comprising the steps of: supplying fluid against the piston to urge the piston in a linear direction.

30. The method as claimed in claim 20 further comprising the steps of: supplying pneumatic fluid against the piston.

31. The method as claimed in claim 20 further comprising manually holding and moving an assembly including the punch, piston and inclined members.

32. The method as claimed in claim 20 wherein the first member having a vertical axis and an angle defined by said vertical axis and the inclined surface, the angle being between 2 to 10 degrees.