Patent Publication Number: US-6213177-B1

Title: Feed wheel

Description:
FIELD OF THE INVENTION 
     This invention relates to a feed wheel particularly, but not exclusively, for use in a wood working machine. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention provides a feed wheel for use in a wood working machine in which the feed wheel is rotated while in driving engagement with the surface of a wood piece to drive the wood piece past a wood working element, for working the wood piece, the wheel having a periphery adapted, such as by the provision of teeth thereon, for driving engagement with the wood piece, and incorporating a one way drive device such that the feed wheel may be driven only in the direction for feeding of the wood piece, being freely rotatable in the direction opposite to that for feeding. 
     In another aspect, the invention provides a feed wheel for use in a wood working machine in which the feed wheel is rotated while in driving engagement with the surface of a wood piece to drive the wood piece past a wood working element, for working the wood piece, the wheel having a periphery adapted, such as by the provision of teeth thereon, for driving engagement with the wood piece, the feed wheel having a rim portion separable from the remainder thereof. By this, when the feed wheel periphery wears it may be replaced by fitting a new rim portion. 
     In another aspect, the invention provides a feed wheel for use in a wood working machine in which the feed wheel is rotated while in driving engagement with the surface of a wood piece to drive the wood piece past a wood working element, for working the wood piece, the wheel having a periphery adapted for driving engagement with the wood piece, the feed wheel having teeth around the circumference thereof, the teeth presenting a forward substantially radial face, and a trailing face which extends at an angle to the substantially radial face, such that the teeth are generally triangular in cross-sectional form, the teeth being arranged such that apices thereof, defined at the junction between the faces thereof, extend at a helix angle relative to the axis of the wheel. The aforementioned angle may be in the range of 15 to 25 degrees, such as for example substantially 20 degrees, and may be such that the apexes extend at the aforementioned angle either in a trailing or advancing direction with respect to the intended direction of rotation of the wheel. The angle presented between the trailing face of each tooth, and the substantially upright face of a succeeding tooth is in the range 58 to 62 degrees. The dimension of the substantially radial face of each tooth reckoned radially of the wheel is within the range of 4 to 7 mm, most preferably substantially 5 mm. The teeth may have one or more circumferential grooves. 
     The invention also provides a wood working machine, having a feed wheel according to the invention, and a method of forming a wear resistant diamond layer on a surface of the feed wheel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is further described by way of example only with reference to the accompanying drawings in which; 
     FIG. 1 is a diagrammatic perspective view of a wood working machine utilising a feed wheel constructed in accordance with the invention; 
     FIG. 2 is a diagrammatic side view of the machine of FIG. 1; 
     FIG. 3 is a diagrammatic end view of the machine of FIG. 1; 
     FIG. 4 is a side view of the feed wheel; 
     FIG. 5 is a top view of the feed wheel of FIG. 4; 
     FIG. 6 is an isometric view illustrating a segment of the peripheral portion of the feed wheel of FIG. 4; 
     FIG. 7 is a view substantially the same as FIG. 5, but illustrating the helix angle of teeth on the periphery of the feed wheel; 
     FIG. 8 is an enlarged side view of the teeth of the feed wheel of FIG. 4; 
     FIG. 9 is a partly sectioned side view of the feed wheel embodying a one-way clutch mechanism in accordance with the invention; 
     FIG. 10 is a side view of a rim portion forming part of a feed wheel in accordance with the embodiment of the invention; 
     FIG. 11 is a top view of the rim portion of FIG. 10; 
     FIGS. 12 and 13 are fragmentary views of segments of various other rim portions constructed in accordance with the invention; 
     FIG. 14 is a cross-section substantially on the line  14 — 14  in FIG. 9; 
     FIG. 15 is a diagrammatic side view of an alternative wood working machine constructed in accordance with the invention; and 
     FIGS.  16 ( a ) and  16 ( b ) illustrate arrangements of a feed wheel of the invention, for feeding wood pieces guided by a fence, for conditions where the fence is positioned at right-hand left-hand sides of the wood piece respectively. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     FIGS. 1 to  3  illustrate diagrammatically a wood working machine  10  having a machine bed  12 , a side fence  14  and a machine head  16 . In use, a wood piece  18  is positioned on the bed  12  adjacent the fence  14  and is advanced in the direction illustrated by the arrow “A” in FIG.  1  and FIG. 2 past the head  16  so that the wood piece is machined. The wood piece is normally held against the side fence  14  during this operation, for purposes of accurately aligning the wood piece with the head  16 . The head  16  may for example be a milling cutter, a saw or the like. 
     In machines of the kind illustrated, it is customary to provide some mechanism for automatically advancing tile wood piece past the machine head. In the present instance, this mechanism, designated generally by reference numeral  18 , includes an arm  20  pivotally connected at the location  22  to a fixed part  23  of the machine, so as to trail backwardly and downwardly from the location  22  to a location somewhat behind the location of the head  16 . At its lower end, the arm  20  carries a bearing housing  21  which carries, for free rotation therewithin, a feed wheel shaft  22 . At one side, over the machine bed  12 , the shaft has affixed thereto a feed wheel  24 . At the other side, the shaft  22  is affixed to a suitable drive means. By way of example only, in this case, the shaft is shown arranged for driving from an electric motor  27 , via a gearbox  25 . 
     The arm  20  is coupled to an extensible hydraulic ram  28  which is actuatable to cause the arm to be rotated about the location  22  from a position (not shown) at which the feed wheel  24  is well above the bed  12  to the position shown in FIGS. 2 and 3 at which it is lowered such that the periphery feed wheel  24  is pressed into engagement with the upper surface of a wood piece  18  which is to be fed through the machine. When in this condition, the feed wheel  24  may be rotated by operation of the motor  25  so as to cause the feed wheel to rotate in the direction indicated by the arrow “B” in FIG. 2, to frictionally engage the upper surface of the wood piece  18  to drive this in the direction “A” as described, for machining of the work piece. 
     FIGS. 4,  5  and  6  illustrate the feed wheel  24  in more detail. In particular, this has teeth  26  arranged around the periphery thereof so as to facilitate frictional engagement with the wood piece  18 , for driving thereof. In the illustrated embodiment, there are two axially spaced peripheral grooves  35  in the surface of the wheel so as to divide each tooth  26  into three tooth portions  32 ,  34 ,  36 . There are thus three rows of such teeth portions arranged in the axial direction of the wheel, although the number of such rows may vary, as described later. 
     In accordance with a specific aspect of the invention, the feed wheel  24  is formed in two parts, a rim part  38  and a hub part  40 . The rim part  38  is shown in more detail in FIGS. 10 to  12 . It carries the teeth  26  having portions  32 ,  34 ,  36  as abovementioned. The teeth  26  are formed on a generally hollow cylindrical outer portion  44  of the part  38 , which portion  44  is integrally formed with an inner annular flange  46  to which the hub part  40  is bolted by bolts  47  (FIG.  4 ). The hub part  40  has an inner axial bore  50  with a keyway  52  such that the hub part can be neatly fitted over the shaft  22  and secured for rotation with respect thereto by insertion of a key (not shown) into the keyway  52  and into a corresponding keyway (also not shown) on the shaft  22 . By this arrangement, when the teeth on the part  38  wear, it is possible to unbolt the part  38  from the part  40  and to replace it with a new part  38 . By this, it is not necessary to replace the whole of the wheel  24  when tooth wear occurs, this resulting in a significant economy. That is to say, it is only necessary to discard part of the wheel  24  rather than the whole of it when wear occurs. 
     It is preferred that the teeth  26  of the wheel  24  be configured in the manner illustrated in FIGS. 7 and 8, in order to facilitate efficient driving of the wood piece. In particular, as shown in FIGS. 7 and 8, the teeth are generally of triangular form, having a generally radial leading face  50 , and a trailing face  52  which is angularly disposed with respect to the respective face  50 . The depth of the teeth, indicated as “D” in FIG. 8, is best selected to be in the range 4 to 7 mm, preferably substantially 5 mm. The selection of this dimension is related to the number of teeth that can be formed around the outside of the wheel. If the dimension “D” is increased, then there are less teeth around the outside of the wheel and less teeth in contact with the timber. If it is increased too far, slipping will occur as between the periphery of the wheel and the wood piece. If “D” is decreased, then there are more teeth around the wheel but the wheel is more likely to be clogged up with fibres from the wood and to stop functioning. 
     The teeth  26  are preferably arranged to such that apices  54  thereof are linear when viewed from the side of the wheel, and extend at a helix angle C as shown in FIG. 7 with respect to the axis of the wheel. It has been found that this angle is best selected to be between 15 and 25 degrees, usually substantially 20 degrees. The angle may be either positive or negative in value, reckoned with respect to the axis of the wheel. If the angle C is increased, then the wood piece tends to be forced harder towards the guide fence  14  and excessive wear of the fence and damage to the timber may occur. If the angle E is decreased, then the timber is not forced towards the fence, and poor machining of the timber is likely to result. 
     The angle E shown in FIG. 8, being the angle between the face  52  of each tooth  26  and the substantially radial face  50  of the next successive tooth around the periphery of the wheel, is best maintained within the range 58 to 62 degrees. If the angle is increased, longer wear life of the wheel is achieved, but the tooth may not grip the wood piece effectively. If the angle is decreased, the tooth may dig into the timber deeper and thus providing better gripping, but the tooth may wear out more quickly. It has been found that selecting the angle in the range 58 to 62 degrees as described provides a good compromise between wear and gripping. 
     In the illustrated embodiments so far described, the periphery of the wheel has two axially displaced grooves  35  so that the teeth  26  are interrupted in the axial direction of the wheel at these locations to form the respective tooth portions  32 ,  34 ,  36 . It has been found that the provision of these grooves facilitates operation. The number of grooves may be selected in accordance with the type of timber being processed. It has been found, for example, to be satisfactory to provide three grooves for soft to medium hardness timber and five grooves for hard timber. FIG. 13 illustrates the case where there are four grooves, and thus each tooth has five tooth portions  132 ,  134 ,  136 ,  138  and  140 . 
     Another problem which arises with use of the machines of the kind shown in FIGS. 1 to  3  is that of “gear drive wind up”. In particular, the drive chain to the wheel may be subjected to intermittent or cyclic portional stress due to the timber work piece encountering intermittent or cyclic variations in the resistance to movement past the machine head  16 . These variations may occur, for example, because of physical variations in the timber structure along its length, or to variations in the machining action of the head  16 . If the feed wheel is an integral construction, keyed directly to the drive shaft  22 , the torsional forces may be much as to cause failure of the drive motor or of any intervening components such as the gearbox  27 . In order to alleviate this problem, it is possible, in accordance with the invention, to form the wheel  24  such that, while it can be driven in the direction required for feeding of the wood piece through the machine, it is freely rotatable in the reverse direction. FIGS. 9 and 14 illustrate a construction of this kind. 
     In FIGS. 9 and 14, the hub part  40  is shown as being formed from a central bearing element  70  having, intermediate its ends, a relatively wide outstanding angular flange  72 . The ring  38  is bolted by bolts  76  to an annular member  78  having an inwardly projecting annular flange  80  at one axial side. The inner circular periphery of the flange  80  slidingly accommodates, and provides a bearing surface for, the outer periphery of the bearing portion  70 . At an axial side of the wheel  24  opposite flange  80 , an annular element  82  is bolted to the element  78  so as to extend in generally parallel spaced disposition with respect to the flange  80 . Element  82  is bolted to the element  78  by means of bolts  84 . The inner circular periphery of element  82  provides a second bearing surface for the bearing element  70 . The flange  72  of the bearing element  70  is cut away at one axial side, at five peripheral locations, to form five pockets  88 . These pockets are closed at the outer periphery thereof by the inner periphery of the element  78 . Within each of the pockets  88  there is disposed a freely rotatable cylindrical element  90  the axes of these being parallel to that of the wheel  24 . A base surface  82  of each pocket  88  extends such, within each pocket, the space between the surface  82  and the periphery of the element  78  increases in a circumferential direction around the axis of the wheel. That is to say, the pockets  88  have an approximately radial dimension “X” at one circumferential end which is greater than the corresponding dimension “Y” at the other circumferential end. The elements  90  are of such diameter that, in the case where the rim part  38  is rotated in the direction “P” shown in FIG. 9, relative to the hub part, the elements  90  tend to move towards the lesser dimensioned (“Y”) end of the pockets  88  to be wedged between the surfaces  82  of the pockets and the inner periphery of the element  78 , thus causing the hub part  40  and rim part  38  to be drivingly coupled together. On the other hand, under the condition of relative rotation of the rim part  38  in the direction opposite to the direction “P”, with respect to the hub part  40 , the elements  90  tend to be moved towards the greater dimension end (“X”) end of the pockets  88 . In consequence of which there is no coupling between the hub part  40  and rim part  38  and relatively free rotation may occur as between these. 
     In order to facilitate movement of the elements  90  in the pockets  88 , a suitable resilient element  92  may be provided in each pocket  88  arranged to provide some resilient bias against the elements  90  in the direction towards the “Y” ends of the pockets  88 . 
     Feed wheels in accordance with the invention may be applied for use in machines of different form to that shown in FIG. 1 to  3 . For example, FIG. 15 shows, in diagrammatic side section, an alternative machine  110 , using feed wheels in accordance with the invention. Here, the bed  112  is formed in two parts  112   a ,  112   b , between which is positioned a cutter head  116   a , having mounted thereon a cutter  177 , the cutter head being slidable on an inclined surface  119  so as to enable it to be vertically moved to vary the extent to which the cutter  117  projects above the bed  112 . In this case several feed wheels  24  are provided to feed the wood piece  18  along the bed, to be cut from the underside by the cutter  117 . In this case, the wheels  24  are arranged at pre-fixed locations. 
     Further, the wheels may be arranged such that the helix angle “C”, which is either positive or negative with respect to the axis of the wheel  24 , is utilised such that the wood piece  18  is, generally, urged towards the fence  14  during its movement through the machine  10 , or  110 . In particular, the apices of the teeth  26 , at the axis of the wheel as viewed from directly above the wheel axis, are disposed so that the ends of the apices at the side of the wheel away from the fence  14  are further advanced in the feed direction than the ends at the side of the wheel closest the fence. This is illustrated diagrammatically in FIGS.  16 ( a ) and  16 ( b ) for cases where the fence  14  is to the right and to the left of the wheel, viewed from above. 
     The wheels may also be provided with a wear-resistant surface such as a wear-resistant hard chromed or diamond layer applied to the teeth to increase the working life of each wheel. In the case of a diamond wear-resistant layer, in particular, the following procedure may be adopted. Firstly, the teeth need to be formed of a magnetic material such as steel. The surface of the teeth needs to be chemically cleaned and etched to remove all traces of oil and foreign matter. The rim part  38  is then immersed in a nickel compound chemical solution, which includes diamond grit, such that a metallic nickel compound is deposited on the surface of the teeth. The diamond grit is simultaneously deposited by method of attraction to thereby form the wear-resistant layer. The metallic nickel compound can be precipitation hardened, if required. 
     While the invention has been described specifically in relation to the working of wood pieces, it can be applied to the working of any work piece having properties which facilitate feeding by use of wheels of the kind described. For example, it may be applied to work pieces capable of being driven by toothed wheels, such as work pieces formed of plastics. 
     The described construction has been advanced merely by way of explanation, and many modifications and variations may be made thereto without departing from the spirit and scope of the invention which includes every novel feature and combination of novel features herein disclosed.