FIELD OF THE INVENTION
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The present invention relates generally to the forest industry, and more specifically to woodworking machines used to transform solid wood into lumber, chips, strands, shavings, and veneer. Most particularly the present invention relates to the knife clamping assemblies used to hold woodworking knives in place in such woodworking machines.
BACKGROUND OF THE INVENTION
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Many forms of woodworking machines are in use in the forest industry. Some are designed to convert solid wood into a plurality of wood chips for the production of chemical or mechanical pulp. Others are directed to the transformation of wood into chips, veneer, and/or shavings for the production of waferboard, oriented strand board, plywood, lumber, or other such wood products.
Common to such machines is the presence of wood-working knives. The knives can be mounted in various arrangements within the machine to act as required upon the wood being processed. Typically, this involves the mounting of one or more knives on a body of conical, cylindrical, or disc form that is rotated under mechanical or electrical power to cause the knives to act upon the wood in an appropriate fashion. These machines further comprise the means necessary to orient and manipulate the wood against the action of the rotating knives.
With some machines, more than one rotating body may be required to transform the wood in the manner desired. Additionally, with some machine designs, the knives may be maintained in a stationary body while the wood is rotated or otherwise manoeuvred against the knives so as to achieve the desired cutting action. What is common with the different arrangements is that the knives are secured to some form of foundation body, or base member, which may be either rotating or stationary, and the knives are brought into relative contact with the wood according to the orientation required to achieve the desired end result.
Common to the aforementioned is that the action of the knives against the wood subjects the knives to considerable cutting forces. The machines must therefore be designed so as to secure the woodworking knives to the base member in a manner to withstand these cutting loads. Since the repeated action of the knives against the wood also results in wear, the machines most also be designed so as to allow for the periodic replacement of the knives. Further, since wood can contain foreign material, such as rock or steel which can be present within the wood itself or embedded or frozen to its exterior, the machine must also be designed so as to allow repairs to be effected in the event of damage to the knives, or other associated machine components.
The most typical means utilised to accomplish the above is to mount the knives in a knife clamping apparatus affixed to the base member. This knife clamping apparatus, often referred to as a knife elating ‘assembly’, serves as an intermediate device for securing the knives within the machine. It is generally sized and shaped so as to secure the knives against the cutting forces, allow for their efficient replacement as required, and is typically constructed so as to be mounted to the base member in a fashion that allows for its replacement in the event of damage.
The demands on the clamping assembly are not trivial. Foremost, the clamping assembly must be constructed so that the knives can be retained in their position under the action of the cutting forces. Such cutting forces are typically high in magnitude, extremely episodic, and are usually varied in direction. The clamping assembly must resist deformation, avoid fatigue, and resist breakage when subjected to the stresses associated with these loads. Additionally, the knife clamping assembly must be constructed so as to be of sufficient rigidity so as to minimize deflections such that the knives are not excessively displaced from their proper position within the machine during operation. This latter requirement is important in most woodworking applications where the knife edge must have an accurate location with respect to the wood being processed or other machine components.
The clamping assembly must also be designed so as to allow for the rapid, reliable, and accurate replacement of the knives. Specifically, the apparatus mast allow for the knives to be easily removed, the clamping assembly cleaned of any wood debris (flakes, chips, sap, etc.), and replacement knives installed in a repeatable and precise fashion. To achieve this end, the individual components that comprise the clamping assembly should be of a design that permits for a high degree of precision in manufacturing.
Reliability is also of prime importance. In particular, the means employed to clamp and unclamp the knives must be such that a predictable and acceptable mechanical joint is obtained under all circumstances. These means typically comprise some form of actuator of a mechanical or hydraulic nature that can allow the assembly to be opened and closed in a controlled and predictable fashion in order that the knives are properly secured at all times. This actuator, with which the workers must interact to accomplish the changes, should be readily accessible and easy to use.
Since woodworking machines of the type herein described typically operate in a production environment, the design of the clamping assembly must also be such that, it is tolerant of the variations that occur under such conditions. This can involve cumbersome working situations where workers need to reach around components of the machine to effectuate a knife change, or limitations in time available between production periods to attend to all aspects of the work in a detailed and thorough fashion. The knife assembly must furthermore exhibit a high degree of fault tolerance so as minor amounts of damage cannot jeopardize the function of the clamping assembly. Such minor damage can easily go unnoticed in a production environment.
To achieve proper integration with the remainder of the machine, the knife clamping assembly must furthermore of a structure that is compatible with the base member. Such bodies, with their varied forms, impose various geometrical and functional constraints. Foremost it must be sized and shaped to provide for reliable and stable mounting within the base member. Additionally, it must be affixed in a manner that permits for the replacement of components in the event of damage.
The requirements of many modern day machines impose additional demands on the knife clamping assembly. Many such machines are by necessity of function compact in nature. The need to operate at evermore increasing production speeds for cost competitiveness has resulted in machine designs with increasingly higher knife counts, and accordingly, limited amounts of space available for the knives and knife clamping assembly on the base member. Accordingly, knife clamping assemblies, as well as the knives they clamp, must be evermore compact to achieve these goals.
Traditionally, knife clamping assemblies need in woodworking machines have been relatively simple devices occupying significant space on the base members in which they mount. The knives used in these assemblies were commonly large planar elements of simple form that were shaped to allow for the repeated sharpening of the cutting edge. These knives, which due to their size were typically capable of sustaining a significant portion of the cutting loads, were generally secured in the clamping assembly in a ‘sandwich’ style arrangement using an actuator of some form. The actuator would cause the clamping components of the assembly to be drawn, together or otherwise displaced so as to secure the knives therebetween.
Typical with such ‘sandwich’ style clamping assemblies is that the line of action of the force developed by the actuator intersects with the knife element, often, towards its middle section. This often necessitates that the knife be formed to allow for the actuator, commonly a threaded fastener, to pass there through. The advantage of such an arrangement is that the majority, or in many cases all of the clamping force generated by the actuator serves to secure the knife between, the clamping components. However as a result of the rather large sizee of the knife elements themselves, the clamping assemblies are typically bulky devices consuming significant space on the base member.
The advent of so called ‘disposable’ knives, often of a ‘reversible’ (or multiple edged) type, has placed increased demands on the clamping assembly. These knives, typically manufactured from higher quality materials, must be small and lightweight for cost effectiveness. Their compact nature precludes them from being primary load bearing elements and renders them significantly more difficult to secure within the clamping assembly.
Blades of the reversible type also pose additional constraints on the clamping assembly in that the clamping components cannot contact the knife is areas adjacent the unexposed cutting edge(s) since these edges can often be damaged from prior use. Already limited due to their smaller size, this further diminishes the support and contact areas that can be employed to maintain the knives in a stable position during operation. Securing such compact knife elements requires that the knives be rigidly clamped with proportionally higher clamping forces than traditional assemblies using larger, regrindable, knife elements.
The most common means to secure knives of a else or a shape that cannot be fastened in a ‘sandwich’ style configuration is to employ a clamping assembly that functions according to the principle of a third order lever. With this arrangement, the force developed by the actuator is applied to a clamping component which pivots abort a fulcrum formed in the assembly. The line of action of the force developed by the actuator is positioned between the fulcrum and the knife. The clamping pressure achieved on the knife is a function of the distances between the fulcrum position, actuator location, and knife contact point according to the principles of a third order lever.
Clamping assemblies that function according to this principle have many advantages. Foremost such an arrangement permits for the line of action of the force generated by the actuator to lie adjacent the knife such that the knife need not be formed to allow the actuator to pass through the knife body itself. This is typically a requirement for securing compact knives, either of disposable, reversible, or regrindable type where the form and size of the knife precludes other clamping means. When properly sized and constructed, clamping assemblies based on this principle can also generate high clamping forces for securing the knives under the action of the cutting forces. Limited only by the space available within the base member, the clamping assembly can typically be sized and shaped to provide for adequate rigidity and sufficient space to accommodate actuators that can develop satisfactory clamping forces so as to be able to secure the knives during operation. Further, simple and reliable third order clamping assemblies can be constructed using only two clamping components and a simple mechanical actuator for securing the knife therebetween.
With such clamping assemblies, the most common configuration is for the actuator to act upon the clamping component positioned towards the outer periphery of the base member. The ‘outer’ clamping component is generally more accessible and can be more readily opened and closed by workers to effectuate the replacement of the knives. With this arrangement, the remainder of the assembly is affixed, to the base member, usually in some form of cavity or ‘pocket’ sized and shaped for this purpose. The actuator draws the outer clamping component against the knife to secure it within the clamping assembly, which remains stationary with respect to the base member. As this outer clamping component often coincides with the topside of the assembly, this arrangement is commonly referred to as ‘topside’ clamping.
With the majority of clamping assemblies, the actuator is typically in the form of a threaded fastener such as a screw, a bolt, or a stud and nut combination. Mechanical fasteners of such, type are simple, inexpensive, reliable, and can provide significant clamping force in a compact form. In order that the driving features of the fastener be readily accessible, it is most common that these be located on the same face or side of the base member as the outer clamping component. This avoids the need for markers to move to other areas in the machine to access the fasteners when changing knives.
The most common arrangement when using mechanical fasteners for the actuator is to have the fastener pass through the outer clamping member and into other assembly components below, or directly info the base member. When tightened, the fastener is gradually drawn against the outer clamping component to develop the contact force necessary to secure the knives in place. To effectuate a knife change, workers tighten or loosen the fastener as required to either release or secure the knives in the assembly.
As a result of their simplicity and ease of use, third order knife assemblies utilising a topside clamping configuration and mechanical fasteners are in widespread use in the type of woodworking machines herein described. They are cost effective, versatile, and have proven reliable in service.
However they are not without problems. According to the principles of a third order lever, the clamping pressure achieved on the knife is a function of the force developed by the actuator and the distances between the fulcrum position, actuator location, and contact point between the cuter clamping component and the knife. For a given configuration, the clamping pressure developed on the knife is directly proportional to the clamping force developed by the actuator. Should the force developed by the actuator be half of that intended by the designer, the clamping pressure developed on the knife shall similarly be at bail the desired value.
Such is often the situation when mechanical fasteners are employed as the actuator. While simple and mechanically reliable, the force developed by the fastener is often difficult to predict end control with accuracy. Such factors as the variation in the fastener's tightening force (torque) and unpredictable nature of friction between contact surfaces result in a wide range of force developed by the fastener.
Further, because of the need for knife assemblies to be of a compact form to integrate properly with the foundation bodies, it is not always possible to achieve a third order configuration that is favourable for the development of high clamping pressures. To do this requires that the fulcrum be positioned far away from the actuator and the knife. With many base members, space constraints limit the placement of the fulcrum. This means that the size of the clamping force, and thereby the ability to carry external cutting loads, is dictated by the capabilities of the actuator, which is often variable anid difficult to control as noted above.
In general, the requirement for compactness and high knife clamping pressures conspire to limit the strength that can be obtained with a third order assembly. While the fastener must be of sufficient size to provide the necessary force for securing the knife under the action of the cutting forces, it cannot be of a size or a form that would consume excessive amounts of space within the assembly. This could result in clamping components that are inadequately sized and shaped for acceptable strength to be achieved. While an oversized fastener may ensure that an adequate preload force is developed under all circumstances, it can result in unacceptable stresses within the individual components that comprise the clamping assembly.
To maximize component strength, most third order clamping assemblies securing knives of a compact nature employ smaller high strength fasteners. These fasteners consume less space in the assembly and allow for proportionally stronger clamping components. However achieving adequate function is dependent on the fasteners being tightened to comparatively high values relative to the fastener site. Further, these smaller fasteners lack rigidity which results in a clamping assembly of lower stiffness such that the displacement of the knife edge under the action of the cutting forces can be problematic.
Given that the reliability of most topside clamped third order assemblies is dependent on adequate preload being developed in the fastener, and in particular those using smaller high strength fasteners, it is typically necessary to ensure that factors that influence the clamping force developed by the bolt are controlled in the field. This often mandates that the fasteners be tightened to precise values using specialized equipment, and that the lubrication, cleanliness, and general condition of the fasteners be scrutinized. In the absence of such measures, inadequate bolt preload can compromise the function of the clamping assembly. This can lead to the knives being improperly secured in service.
Alternatives to topside clamped third order clamping assemblies exist. Such designs are often directed at eliminating the aforementioned dependence on adequate preload being developed by the actuator, or to circumvent space limitations on the base member such that high strength arrangements can be achieved.
For example, it is sometimes advantageous to construct assemblies that have the inner clamping component as the member being actuated. With this arrangement, the assembly is affixed and held stationary within a cavity or pocket formed for this purpose on the ‘underside’ of the base member. The actuator draws the inner clamping component against the knife to secure it in place within the clamping assembly. As with topside clamping arrangements, such underside clamping assemblies also frequently work according to the principles of a third order lever.
One of the main advantages of underside clamping arrangements is that they can often make a more effective use of space within the machine. The clamping assemblies can often be made comparatively larger than their topside mounted counterparts while still maintaining good integration with the base member. This permits for stronger and more rigid components to be constructed, and in the case of third order assemblies, a more favourable configuration for the development of high clamping pressures. Since the cutting forces for most of the woodworking machines herein described are generally directed against the knife from the underside, such underside arrangements are also favourable for reasons of strength and stiffness.
Of late, ‘pivot’ clamping arrangements that function according to the principles of a first order lever have materialized. With such configurations, the force developed by the actuator is applied to a clamping component which pivots about a fulcrum formed in the assembly. As per one principles of a first order lever, the line of action of the force developed by the actuator is located askew of both the fulcrum and the knife thereby allowing knives of a compact nature to be secured. However, unlike third order levers, the fulcrum's location is between the actuator and the contact point on the knife. When in use, the actuator pivots the clamping component about she fulcrum to secure the knife in place.
Such pivot clamping arrangements allow for favourable first order configurations to be achieved such that a high percentage of the actuator's force can be applied to the knife. This permits the actuator, typically a threaded fastener, to be made smaller or fewer in number while achieving the high preload force desired. This further allows the individual clamping components that comprise the assembly to be made rigid yielding an assembly of high overall stiffness. Since the line of action of the force developed by the actuator is also askew of the knife, such arrangements are generally well suited for securing knives of a compact nature. An example of such a first order pivot clamping assembly can be found in U.S. Pat. No. 5,996,655 to CAE Machinery Ltd.
While the aforementioned alternatives offer advantages in the form of stronger more rigid clamping assemblies that are less susceptible to inadequate preload being developed by the actuator, they suffer from some notable disadvantages as well. In general, such assemblies do not exhibit the same high ease of use as simple third order clamping assemblies constructed from two clamping components. As a result of reduced accessibility or added complexity, it can be more difficult for workers to make a knife change, in particular to clean the assembly of any wood debris. Such material, if left in place, could compromise the function and reliability of the assembly.
Pivot style arrangements and underside clamping configurations are also generally of a form that preclude their use in many types of woodworking machines. Generally as a result of their size and shape, they do not integrate well with all forms of base members and cannot be easily retrofitted to existing machines. This precludes their use in many applications for which their advantages would in general be beneficial.
Further, the drive for cost competitiveness has also pushed manufacturers to adopt more standardised knife assembly designs that can foe applied to a broad spectrum of woodworking machines. Standardised knife clamping assembly designs are advantageous for the producer and consumer alike. The producer benefits from greater economies of scale final allow for production efficiencies. The consumer benefits from reduced component costs and fewer knife assembly components being required in inventory to support more than one type of woodworking machine in one production facility.
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OF THE INVENTION
What is therefore required is an improved ‘top’ clamping assembly for the clamping of compact knives that overcomes one or more of the aforementioned problems. It is preferably compact and of a form that it can be readily adapted to many types of wood working machines. Further it is preferably of high strength to allow for knife elements of a compact nature to be rigidly secured to the base member at all times. It is preferably of simple design so that the components and actuator that comprise its structure are of reliable construction and are cost effective to produce. Further, it preferably provides for high ease of use such that replacement of the knives can foe accomplished swiftly, reliably, and in a safe manner.
The present invention accomplishes the above by utilising a novel seating arrangement for at least one of the clamping components whereby the position and orientation of the contact surfaces are distributed over three discrete positions such that increased mechanical advantage results. The preferred form of the invention is further configured to take advantage of frictional forces to improve the ability of the clamping assembly to withstand loads that arise during use.
By forming clamping components according to the present invention knife clamping assemblies can be constructed that are favourably sized and shaped such that they can be applied to many different types of woodworking machines. This permits a standardised clamping assembly to fee used in many applications while providing for a compact design with high reliability. The preferred form of the invention also provides for a clamping assembly that is easy to use, allowing for the fast and efficient rotation or replacement of knives having worn or damaged edges while permitting the clamping components to be of rigid construction and of simple shape such that they are cost effective to produce.
Therefore, according to one aspect of the present invention, there is provided a clamping assembly for clamping one or more knife elements onto a woodworking machine, said clamping assembly comprising:
a clamping component comprising a body, said body being sized and shaped to have three discrete contact positions distributed on said body, said three discrete contact positions comprising a fulcrum located generally at one end, a knife abutting portion located generally at the other end for abutting said one or more knife elements, and a bearing surface located elsewhere; and
an actuator for applying a clamping force to said body along a clamping axis located intermediate of said knife abutting portion and said fulcrum;
said fulcrum being formed as a substantially planar surface wherein a line normal to said fulcrum is at an angle to said clamping axis;
said bearing surface being formed as a substantially planar surface positioned on said body wherein a line normal to said bearing surface intersects said line normal to said fulcrum at a position outside of said clamping component at a location farther askew of said clamping axis than said fulcrum.
According to another aspect of the present invention there is provided a clamping component for use in securing one or more knife elements onto a base member of a wood working machine, said clamping component comprising:
a body sired and shaped to have at least three discrete contact positions distributed on said body, said three discrete contact positions comprising, (1) a fulcrum, located generally at one end, (2) a knife abutting portion, located generally at the other end, for abutting said, one or more knife elements, end (3) a bearing surface located elsewhere on said body;
said body further including an opening through said body, said opening having an axis located intermediate of said knife abutting portion and said fulcrum;
said fulcrum being formed as a substantially planar surface wherein a line normal to said substantially planar surface is positioned at an angle to said axis of said opening.
In yet another aspect of the present invention, there is provided a clamping assembly for clamping one or more knife elements onto a woodworking machine, said clamping assembly comprising:
a clamping component sized and shaped to have at least three discrete contact positions, said discrete contact positions comprising a fulcrum located generally at one end, a knife abutting portion located generally at the other end for abutting said one or more knife elements, and a bearing surface located elsewhere; and
an actuator for applying a clamping force along a clamping axis located intermediate of said knife abutting portion and said fulcrum;
said fulcrum being formed wherein the application of said clamping force results in a reaction force developed at said fulcrum having a line of action that is at an angle to said clamping axis;
said bearing surface being sized, shaped, oriented, and positioned wherein the application of sale clamping force results in a reaction force developed at said bearing surface having a line of action that intersects with said line of action of said reaction force developed at said fulcrum at a position outside of said clamping component at a location farther askew of said clamping axis than said fulcrum.
In yet a further aspect of the present invention, there is provided a clamping assembly for clamping one or more knife elements onto a base member of a woodworking machine, said clamping assembly comprising:
first and second clamping components for securing said one or more knife elements therebetween, said first clamping component abutting said second clamping component at least at one location;
said first clamping component being sized and shaped to have three distinct contact positions, said distinct contact positions comprising, (1) a fulcrum located generally at one end, (2) a knife abutting portion, located generally at the other end, for abutting said one or more knife elements, and (3) a bearing surface located elsewhere; and
an actuator for applying a clamping; force to said first clamping component along a clamping axis located intermediate of said knife abutting portion and said fulcrum;
said fulcrum being formed as a substantially planar surface wherein a line normal to said substantially planar surface is at an angle to said clamping axis;
said bearing surface being sized, shaped, oriented, and positioned wherein a line normal to said bearing surface intersects said line normal to said fulcrum at a position outside of said first clamping component at a location farther askew of said clamping axis than said fulcrum.
In one preferred embodiment the clamping assembly is formed of a first clamping component, a second clamping component and an actuator for securing one or more knife elements therebetween, wherein the first clamping component abuts the second clamping component at a fulcrum and the first clamping component pivots about the fulcrum under the action of the clamping force applied by the actuator. A bearing surface, sized, shaped, oriented and positioned on the first clamping component to cooperate with, the fulcrum abuts the second clamping component so as to develop increased mechanical advantage and resist unclamping forces generated by the interaction of the one or more knife elements with the wood being processed. In another embodiment the bearing surface of the first clamping component abuts a base member, or alternately other components attached to the base member.
BRIEF DESCRIPTION OF THE DRAWINGS
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Reference will now be made, by way of example only, to preferred embodiments of the invention as depicted in the attached drawings, in which:
FIG. 1 is view of a typical prior art clapping assembly;
FIG. 2 is a view of a first embodiment of the present invention;
FIG. 3 is a variation of the embodiment of FIG. 2; and
FIG. 4 is a second embodiment of the present invention.
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OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a typical prior art knife clamping assembly constructed according to the principles of a third order lever. With this arrangement, the force developed by an actuator, in the form of a screw 10, is applied to a clamping component 12 which pivots about a fulcrum 14 formed in the assembly. The line of action of the force developed by the screw 10, shown as Fb, is positioned between the fulcrum 14 and the location where the clamping component 12 abuts a knife element 16.
As can be seen in FIG. 1, the fulcrum 14 is formed of two opposing inclined surfaces that allow the actuated clamping component 12 to be engaged, or interlocked, with the member which it abuts. The two opposing inclined surfaces allow the clamping component 12 to pivot under the action of the force developed by the screw 10 but restrict its movement in a direction parallel to and perpendicular to the line of action of the force developed by the screw 10. As a result of the shape of the fulcrum 14, clamping component 12 cannot slide in a direction that is orthogonal to the line of action of the screw 10.
As per the principles of a third order lever, the force applied to the knife element 16 under the action of the force developed by the screw 10 is a function of the distance between the fulcrum position, screw location, and contact point with the knife element 16. Most specifically, this force is a function of the distance between the line of action of the screw 10 and the fulcrum 14 and the distance between the line of action of the screw 10 and the location where clamping component 12 abuts knife element 16. In FIG. 1, these distances are illustrated as ‘D’ and ‘d’ respectively.
Key to the understanding the present invention is the point at the fulcrum 14 about which the distance D is determined. In order to establish the fraction of the force developed by the screw 10 that is applied to the knife element 16, it is necessary to examine the forces developed at the fulcrum 16. While with most third order arrangements this point will coincide closely with the physical location in which the actuated clamping component pivots, analysis of the present invention will show that this not necessarily be so.
Shown in FIG. 1 are the two reaction forces, R2 and R3, developed at each of the opposing inclined surfaces which comprise the fulcrum 14 under the action of the force Fb developed by the screw 10. For the sake of simplifying the analysis, friction is not considered and the reaction forces R2 and R3 are considered to pass through the centre of these surfaces which would coincide with the approximate centre of pressure. Although this simplified approach is taken in the interest of clarity, the present arguments apply equally to the situation where friction is considered as a later discussion will show.
Considering the case of no friction, the line of action of forces R2 and R3 developed at the fulcrum 14 will be normal to the surfaces and will be directed to resist the force developed by the screw 10. Turning to FIG. 1, it can be seen that the line of action of these reaction forces R2 and R3 intersect at a point in space that is intermediate the opposed inclined surfaces comprising the fulcrum 14. This point is identified in the figure as ‘V’.
Examination of point V reveals that only the forces developed by the screw 10 and the reaction force developed at the knife element 16, shown as Fk, can act to pivot clamping component 12 about this point. Reaction forces R2 and R3 cannot act to rotate clamping component 12 about this position since their lines of action pass through this location. Accordingly, point V represents the position about which the distance D should be measured to determine the fraction of the force developed by the screw 10 that must be resisted by the knife element 16. This point can therefore be conveniently considered as a ‘virtual fulcrum’ since it is about this point which the laws of a third order lever apply.
Although prior art clamping assemblies functioning according to the principles of a third order lever exist having varied shapes and forms, the fraction of the force developed by the actuator that is applied to the knife element is dictated by how far askew the virtual fulcrum is positioned from the actuator. The greater the distance the virtual fulcrum is located from the line of action of the force developed by the actuator, the greater the fraction of the actuator\'s force that will be applied to the knife element. This defines the mechanical advantage of the clamping assembly. Greater mechanical advantage results as the distance the virtual fulcrum is located askew of the line of action of the force developed by the actuator is increased.
Turning to FIG. 2, a first, embodiment of the present invention is shown. A base member 100 forming a rotatable foundation body of a woodworking machine of cylindrical form is shown. For ease of reference only a part of base member 100 is illustrated. It will be understood that the present invention may be applied to many different types of woodworking machines with foundation bodies of conical, cylindrical, or disc form and showing base member 100 as a cylindrical segment is by way of example only. Further, base members as described herein may also be stationary as it will be understood that the current invention comprehends stationary base members where the wood is maneuvered in an appropriate fashion to achieve the desired end result.
Within base member 100 is formed a pocket 102 into which a clamping assembly 104 is inserted. The clamping assembly 104 includes a rear clamping component 106 and a front clamping component 108. In this specification, the terms rear and front are used to describe their position relative to the direction of movement of the base member 100 with respect to the wood being processed (not shown). Front clamping component 108 is positioned towards the direction of movement of clamping assembly 104 whereas rear clamping component 106 is positioned away from the direction of movement. In this specification the terms front and rear are to be read interchangeably with the terms inner and outer since the front clamping component is positioned towards the inside of base member 100 which comprises the rotating cylindrical body.
Within pocket 102 is affixed inner clamping component 108 using means (not shown) that result in it being rigidly connected to base member 100. Forming part of pocket 102 is a bottom support face 103 and a rear support face 105 for abutting the corresponding contact surfaces on inner clamping component 108. Located between support faces 103 and 105 is a radiused corner 107 present for stress reduction reasons. To permit the inner clamping component to achieve flush engagement with support surfaces 103 and 105, a chamfer 109 is provided on inner clamping component 108 between the two orthogonal surfaces abutting base member 100. Although abutting inner clamping component 108, it will be noted that pocket 102 is formed such that outer clamping component 106 is free of contact with any of the faces of pocket 102 such that a gap 140 is present between base member 100 and outer clamping component 106.
Clamping assembly 104 further includes an actuator for actuating outer clamping component 106. In this embodiment, the actuator is a threaded fastener in the form of a screw 110 with a head 118, which most preferably is located within a recess 122 formed in the outer surface 120 of outer clamping component 106. The screw 110 passes through openings 112 and 114 in outer clamping component 106 and inner clamping component 108 respectively and is threaded into threads 116 formed in base member 100. While a threaded screw 110 is shown as the actuator, it will be understood that the present invention comprehends other clamping means, each as hydraulic mechanisms, electro mechanical actuators and the like.
Secured within the clamping assembly 104 is a compact knife element 124 which is illustrated as a ‘reversible’ (or indexable) type having two opposed cutting edges. The knits element 124 is shown clamped between the outer clamping component 108 and the inner clamping component 108 generally at one end. At the other end of the clamping assembly 104 a fulcrum 126 is located. The fulcrum 126 forms a point about which outer clamping component 106 can pivot which along with the knife abutting portion 125, form discrete positions for supporting outer clamping component 106 wider the action of the screw 110. Reflecting a third order lever arrangement, the screw 110 is positioned between the fulcrum 126 and knife element 124.
Also present within the assembly are a bearing surface 130 on outer clamping component 106 and an opposing contact surface 132 on inner clamping component 108 about which bearing surface 130 abuts. Along with fulcrum 124 and the knife abutting portion 125 of outer clamping component 106, bearing surface 130 comprises a third discrete position about which contact with adjoining members occurs. It will be noted that these contact points are positioned at separate spaced apart locations on outer clamping component 106 with each having specific functions as will be explained in greater detail below.
When tightened, the head 118 of screw 110 is gradually drawn against outer clamping component 106 such that a clamping force is developed. This force, shown as Fb in FIG. 2, is directed against outer clamping component 106 along a line of action that is parallel with the axis of the screw. This axis, indicated at 128 and defined as the clamping axis, coincides with the line of action of the clamping force developed by the actuator.
During tightening, the clamping force Fb developed by the screw 110 is resisted at both ends of outer clamping component 106 by a reaction force developed against the knife element 124, shown as Fk, and a reaction force developed against the fulcrum 126, shown as R2. Reaction force Fk acts to secure knife element 124 against inner clamping component 108 which is secured within pocket 102 of base member 100. It will be noted that bearing surface 130, formed as a substantially planar surface oriented mainly parallel to clamping axis 120, cannot offer any resistance to clamping force Fb.
Due to the geometry, if there were no bearing surface 130 abutting opposing contact surface 132 on inner clamping component 108, the force of the screw 110 would cause the outer clamping component 106 to move rearward, specifically deeper into the pocket 102. This is due to the fact that the contact surface comprising the fulcrum 126 is substantially planar and is inclined relative the direction in which the clamping force Fb is applied. This inclination, indicated by the angle θ formed between the line of action of reaction force R2 and the direction in which clamping force Fb is applied, is approximately 30 degrees in this embodiment.
Although the knife abutting and 125 is contoured such that it engages knife element 124 at its backside, the front side of knife element 124 is shaped such that it does not engage inner clamping component 108 in a fashion that would positively restrict its movement. In this manner, outer clamping component 106 is, at either end, free to slide relative to inner clamping component 108 when a clamping force is applied along clamping axis 128. This natural tendency to slide is resisted by the presence of the bearing surface 130 abutting opposing contact surface 132 on inner clamping component 108. Because of the presence of bearing surface 130 and the opposing contact surface 132 on inner clamping component 108, instead of sliding, a further reaction force arises, which is shown as R3.
Unlike the prior art assembly illustrated in FIG. 1, it will be noted that fulcrum 120 is not formed to engage or interlock the inner clamping component 108. While shaped to allow outer clamping component 106 to pivot, the substantially planar surface comprising the fulcrum 136 is not formed to positively resist forces acting along its face, hue to the shape and orientation of fulcrum 126 relative to the clamping axis 128, fulcrum 126 cannot balance the reaction forces that develop against outer clamping component 106. Most specifically, the component of the clamping force Fb and reaction force Fk directed along the surface of fulcrum 126 must be resisted elsewhere if a state of equilibrium is to be achieved.
Accordingly, fulcrum 136 can be considered as ‘unbalanced’ since it lacks the ability to counteract the reaction forces that develop on outer clamping component 106 under the action of the screw 10, or equally, under an externally applied force directed against the knife, element 10 that acts in this direction. This contrasts with the ‘balanced’ arrangement of the prior art device of FIG. 1 that occurs when the pivot point is formed as two opposed inclined surfaces or other alternate forms that result in the actuated clamping component remaining stable in the clamping assembly under the action of the clamping force or any externally applied loads.
Returning to FIG. 2, examination of the structure of inner clamping component 103 and knife element 124 shows that these elements also lack the ability for the knife abutting end of outer clamping component 106 to counteract forces directed along fulcrum 126. Accordingly, the component of the clamping force along this face, or any external loads that are applied to the knife element 124 that act in this direction, must be resisted elsewhere in the assembly.
Preferably this is accomplished by utilizing a separate bearing surface suitably sized, shaped, oriented, and positioned to resist loads that cannot be borne elsewhere. Most importantly, this bearing surface is strategically positioned to increase the mechanical advantage achieved with the clamping assembly. By appropriately sizing, shaping, positioning and orienting the bearing surface on the actuated clapping component such that it cooperates with a separate fulcrum that has similarly been approptiately sized, shaped, oriented, and positioned, increased mechanical advantage can be obtained as will be explained below.