Patent Publication Number: US-8540320-B2

Title: Slotted shank bit holder

Description:
This invention relates generally to road milling, road planing, trenching and mining equipment and, more particularly, to an improvement in a quick change bit holder for use in an assembly including bits, bit holders and bit blocks. 
     BACKGROUND OF THE INVENTION 
     Road milling, road planing, mining and trenching equipment frequently utilize similar cutting bits and bit assemblies for ripping up old road surfaces, digging trenches for infrastructure or construction purposes, and for mining various minerals. Bit assemblies for these differing applications may use similarly shaped but differently sized bits and bit assemblies. The shanks of road milling bits may approximate ¾ inch in diameter. Road planing bits are larger. Mining bit shanks may very from 1 to 1½ inches in diameter, and trenching bits may be even bigger. Additionally, the length of bit shanks may vary in that road milling bits may not extend completely through a central through bore of a bit holder, while bit shanks used for road planing, trenching and/or mining may extend completely through the bit holder and be retained or fastened on the back side of the bit holder bore. 
     One such apparatus for holding a cutting bit is shown in U.S. Pat. No. 5,302,005, issued to O&#39;Neill on Apr. 12, 1994. 
     A bit holder design similar to that shown in FIG. 7 of the O&#39;Neill &#39;005 patent is utilized in the mining industry. The bit holder in the O&#39;Neill &#39;005 design is press fit into the bit block and the dimensions of the outside of the bit holder shank as provided on original equipment machinery are a maximum of 0.005 larger than the corresponding dimensions of the bit block bore. The press or interference fit portions of the bit holder are the cylindrical portions of the outside of the bit holder shank. The central tapered portion of the bit holder shank are less than a seating taper, i.e., less than about 3½ degrees per side. In operation, however, it is understood that typically a multiple set of replacement oversized bit holders are carried in the field with the equipment because of the impacting and abuse that the mining operation imparts on the bit holders and bit blocks of the bit assembly. 
     It has been discovered that after some use, the press fit on original equipment bit holders becomes loose and tends to pop out of the bit blocks. A first replacement bit holder is utilized that is 0.010 oversize to fit where the original equipment 0.003-0.005 oversize bit holder originally fit. Additionally, 0.015 oversize bit holders and 0.020 oversize bit holders are also carried in the field to replace the 0.010 and 0.015 oversize bit holders when they become loose and also tend to pop out of the bit block bore after extended use. This entire cycle of 0.005, 0.010, 0.015 and 0.020 oversize bit holders may be utilized during the lifespan of a drum or chain assembly on which the bit blocks are mounted. 
     After reviewing the structure of the bit assemblies shown in the &#39;005 patent, especially those with multiple differing sized, cylindrical upper and lower shank portions, it became apparent to me that the tolerances which need to be met to provide satisfactory surface contact between both the upper and lower cylindrical shank surfaces on the bit holder and their counterparts on the bit block bore are very difficult and costly to achieve, to prevent separation of the holder from the bit block bore in the extreme cutting conditions encountered in road planing, trench digging and mining operations. The solid tapered surfaces also complicate the matching of complementary surfaces between the two parts. 
     More than likely, press fitting the bit holder in the bit block quickly, or in the field, results in a mis-match of at least one pair of the two pairs of complementary cylindrical surfaces. Any such mis-match would result in voids between at least portions of the adjacent cylindrical surfaces. In use, these voids would aid in movement between the bit holder shank and bit block bore that would increase over time. Eventually, the enlarging movement would deform the adjacent parts until the bit holder would become loose and eject out of the bit block, which is what has happened in the field. 
     A need has arisen for an improved bit holder, generally of the type used in the O&#39;Neill &#39;005, patent that will remain mounted in its bit block bore during use for an extended period of time. 
     Another object of the present invention is the provision of an improved bit holder that may be inserted in a bit block bore with a greater interference fit such that it will remain mounted in that bore during abusive use and for an extended period of time, and yet matingly receive the shank of a bit when that the shank extends completely through the central bore of the improved bit holder to prevent deleterious movement between the bit shank and bit holder bore. 
     SUMMARY OF THE INVENTION 
     The invention resides in a bit holder that comprises a front body portion. It also includes a rear shank portion that extends axially from the front body portion. It has a central bore that extends axially through both the front body portion and the rear shank portion. An axially oriented slot means extends along at least a portion of the shank in order to provide an open area into which portions of the shank may collapse as the shank is pressed onto a bit block bore. It further includes relief means on the bit block bore internally adjacent the slot means for providing a substantially cylindrical bit holder bore when the shank is pressed onto the bit block bore. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention may best be understood from the following detailed description of a currently illustrated embodiment thereof taken in conjunction with the accompanying drawings wherein like numerals refer to like parts, and in which: 
         FIG. 1  is a side elevational view of a bit assembly constructed in accordance with the present invention including a mining bit, a bit holder shown in cross-section and a bit block therefor also shown in vertical cross-section; 
         FIG. 2  is a detail exploded view of the bit holder and bit block shown in cross-section in  FIG. 1 ; 
         FIG. 3  is an enlarged perspective view of the bit holder of the present invention; 
         FIG. 4  is a cross-sectional view of an enlarged cross-sectional view of the bit holder shown in  FIG. 3  taken substantially along lines  4 - 4  of  FIG. 3 ; 
         FIG. 5  is a top plan view of the bit holder shown in  FIG. 3  as it appears when inserted in a bit block; and 
         FIG. 6  is a cross-sectional view of a bit holder similar to  FIG. 4  as it would appear inserted in the bit block as shown in  FIG. 1 . 
         FIG. 7  is a cross section view of a modification of the bit holder of the present invention including a stepped, discontinuous central bore. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
     Referring to  FIGS. 1 ,  2  and  3 , the typical bit assembly used in mining is generally indicated at  10 , and includes, in combination, a bit, generally indicated at  11 , which fits into a bit holder, constructed in accordance with the present invention, which in turn fits into a bit block  13 . The bit block is mounted on a rotatable drum or continuous chain assembly (not shown). As shown most clearly in  FIG. 1 , in this bit assembly, which is used mainly in mining operations, the bit  11  includes a forward body portion  11   a  and a generally cylindrical shank  11   b  that extends axially therefrom and is sized lengthwise to extend completely through the bit holder  12  in which it is mounted so that it extends out the rear thereof and into an opening  13   a  in the bit block  13  through which a spring clip or other device (not shown) may be fastened adjacent the distal end of the bit shank. The bit block  13 , into which the bit holder  12  is mounted includes a base  14  which may be flat as shown or slightly concave to fit on a cylindrical drum (not shown) and an upper body portion  15  which can be generally annular in shape and includes a stepped bore, generally indicated at  16  and an annular top surface  17 . 
     Referring to  FIG. 2 , the bit block bore, generally indicated at  16  is a multi-step generally cylindrical bore that extends from the top annular surface  17  to the recess  13   a  toward the base  14  of the bit block  13 . Inwardly adjacent the top annular bit holder mounting surface  17  on the bit block is a beveled edge  18  and inwardly thereof is a first or top cylindrical press fit portion  20  of about 1.855 inch diameter which extends 1 5/32 inch axially along the bore. At the bottom end of first press fit portion  20  is a transition taper portion  21  that is about 5/32 inch in axial length and tapers at an included angle greater than 7 degrees so that it is a slip taper and not a locking taper. At the bottom of slip taper  21  is a second or smaller hollow cylindrical press fit portion  22  of about 1.812 inches in diameter that extends axially therefrom to extend into the upper side of the bit block recess  13   a.    
     The bit holder  12  as shown in  FIGS. 1-3 , includes a body or front portion, generally indicated at  24 , and a shank portion, generally indicated at  25 , extending axially from the base of the body portion. The top or body portion of the bit holder  12  includes, in this illustrated embodiment, a generally flat annular surface  26 , a frustoconical side wall  27  extending at an angle axially from the outer edge of the flat annular surface and an outer generally cylindrical wall  28  that extends to a bottom wall which is a generally radially extending annular ring  30 . The bit holder bore extends from the inside of the annular top surface  26  with a beveled edge  31 . From the bottom of the beveled edge, a cylindrical portion  32  extends axially beyond the axial position of the flat annular surface  30  of the outside of the body portion to a circumferential line shown at  33  in  FIG. 2 . 
     Circumferential line  33  that is about 23/32 inch from the top flat surface in this embodiment, divides the cylindrical portion  32  of the bit holder bore from an outwardly tapering portion  34  that extends from about line  33  to the distal end  35  of the bit holder shank. It should be noted that the position of line  33  is somewhat variable along the length of shank  25 . It is also variable with respect to its location relative to the inner end  36   a  of slot  36 . Additionally, a hollow slot, generally indicated at  36 , is in this embodiment, approximately ⅛ inch in width and extends from the annular distal end  35  of the shank upward to about the center of the rounded or circular inner end  36   a  of the slot which centerline runs through the bore dividing line  33 . The significance of these features will be discussed in greater detail below. 
     The material used for the bit holder has to have spring steel characteristics. 4140, 8640, 4340 or similar steels are a preferred material for the heaviest duty cutting applications. It may be possible to use other steels for lighter applications. Also, while forged steel is preferred, holders may be formed from bar stock. The bit holder material has to have a substantial elastic memory in the range of the deformations (radial collapses) shown herein. 
     Referring to  FIGS. 3 ,  4 ,  5  and  6 , the illustrated embodiment of the bit holder of the present invention  12  is shown in greater detail.  FIG. 3  discloses that the outside of the shank, generally indicated at  25  is complementary to the bore  16  of the bit block  13 . The front or body portion, generally indicated at  24  has been described in connection with  FIGS. 1 and 2  previously. The interior most portion of the back annular face  30  of the body of the bit holder  12  includes an annular rounded fillet  40  that provides a less stress-inducing transition between the front body portion  24  and the back shank  25 . The shank  25  includes an upper generally cylindrical portion  41  of 1.870 inches in diameter extending axially from the rounded shoulder  40 . In the illustrated embodiment, after 11/16 inch, the generally cylindrical upper portion  41  turns into a tapered portion  42  which has a slip taper, not a locking taper. At the bottom of taper portion  42 , which 3/16 inch in axial length tapering at 6 degrees/side, a lower generally cylindrical portion  43  of 1.827 inches in diameter extends to the distal end  35  of the shank. As shown in  FIG. 3 , the generally circular inward end  36   a  of slot  36  extends generally from about the juncture of the curved shoulder  40  and the upper portion  41  of shank  25  axially toward the distal end of the shank. At the bottom of the circular inner end  36   a , the slot extends from there axially to the distal end  35  of the shank  25 . As indicated in this illustrated embodiment, the width of the slot approximates ⅛ inch and the diameter of the circular inner end approximates ¼ inch. While prior bit holders that had unslotted shanks have been used in connection with the bit blocks  13  shown in  FIGS. 1 and 2 , these prior bit holders were made to press or interference fit in the bit blocks and with an outer diameter approximating 1.85 inches, the standard heavy duty press fit indicated an interference of approximately 0.005 inch in both the upper shank portion  41  and the lower shank portion  43  (which is 1.80 inches in diameter before insertion). 
     As mentioned in the background above, these prior bit holders during use worked themselves out of the bit blocks they were mounted in. Then successive 0.005 and 0.010 oversize (over the original 0.003-0.005 oversize) bit holders were used to serially replace the bit holders after they worked themselves out of their bit blocks. This necessitated having on hand in the field substantial spare parts. The present invention, when used as original equipment, has drastically reduced the need for spare bit holders in the field. It is a one-size-fits-all solution wherein the shank is able to expand radially like a roll pin and retain a bit holder in its bit block even after substantial use and wear. If used as a replacement part, the bit holder of the invention becomes the last spare needed for the useful life of the bit block. If replacement of the sleeve is necessary due to excessive sleeve bore wear, this new style sleeve will fit the same base block. 
     In this embodiment, the circular end portion  36   a  of slot  36  is approximately ¼ inch in diameter, although it will be understood that almost any rounded shape that lessens the possibility of stress fractures may be used within the scope of the present invention. The slot width is determined by the need for more or less radial holding force. 
     Referring to  FIGS. 4 and 6 , in one aspect of the present invention, the outwardly tapered bit holder bore in the shank portion of the bit holder is shown in slightly exaggerated form for emphasis. In this embodiment, the diameter C of the bit holder bore is 1.195 inches from the annular top surface  26  to the centerline  33  of the slot inner circular end  36 . 
     Originally, before deciding on the taper shown at D in  FIG. 4 , an original shank bit holder was slotted and then inserted in its bit block and the collapsed dimensions at the positions J, K, L and M in  FIG. 6  were measured as 1.190, 1.185, 1.179 and 1.175 inches, respectively. In order to reach the desired substantially straight bit holder bore of 1.195 ±0.005, the required taper for an uncompressed shank bore was computed to be 0.020, substantially equal to the oversize of the shank outer diameter. It will be understood that a single or multiple step (discontinuous) bore may also be used if the successive steps are small. Although the bit holder shank is not a continuous cylinder, a continuous taper works well for this application. 
     Dimension D adjacent the rear annular flange surface  35  of shank  25  is 0.007 inch per side or 0.015 inch, on a diameter, which yields an overall diameter E greater than dimension C or 1.210 inches. If the diameter C plus 0.015 adjacent the distal end  35  of the shank is 0.015 greater than dimension C, dimension F, the outer diameter of the lower shank cylindrical portion, would also be 0.015 greater than the bottom or small cylinder bore  22  of the bit block  13 . For the illustrated embodiment, it has been determined that about 6,500 pounds of radial force is required to collapse the sleeve outer diameter 0.015 at the distal end portion of the shank. By collapsing the sleeve 0.015 of an inch, the taper D shown in  FIG. 4  disappears and any excess diameter in the shank collapses the slot  36  similarly to that shown in  FIG. 1 . 
     When inserted in the bit block, as shown in  FIG. 1 , the bit holder bore  12   a  takes on the dimensions shown in  FIG. 6 , i.e., the bit holder bore is substantially straight and nearly cylindrical through its length. Thus, the bit holder bore is capable of accepting the bit shank  11   b  in a satisfactory configuration. The bit  11  is still capable of rotating in the bit holder bore  12   a . Also, the fit between the shank  11   b  of the bit  11  and the bit holder bore  12   a  is such that the shank does not slap or pound the sides of the bit holder bore  12   a  during use to wear the fit therebetween in a speedy manner. 
     When the bit holder  12  is inserted in the bit block bore  16 , as shown in  FIG. 1 , the outside of the shank  25  of the bit holder takes on the dimensions shown in  FIG. 5 . The diameter of the upper shank cylindrical portion  41  is 1.870 inches and the diameter of the lower shank cylindrical portion  43  is 1.830 inches. Referring to  FIG. 6 , as indicated above, with the upper and lower cylindrical shank portions of the prior art being circumferentially solid, i.e., without a slot, the tolerances necessary to provide cylindrical surface contact both at the upper shank cylindrical portion  41  and the lower shank cylindrical portion  43  are too exacting for complete or proper fit under normal mass commercial manufacturing techniques. Therefore, it was more likely in the prior art that possibly only one of the upper or lower shank cylindrical portions would be snugly fit in the bit block bore, if either. The resulting loose fit of the other of the upper or lower cylindrical shank portions would allow excessive movement to occur between the bit block bore and the bit holder shank. This movement during use would shorten the life of the bit holder-bit block assembly and, has resulted in bit holders popping out of the bit blocks during use. The ability of the slotted shank as shown in  FIG. 5  to change its shape provides for a more complete surface fit or contact between the upper shank cylindrical portion of the bit holder shank and the upper cylindrical portion of the bit block bore together with the lower portion of the bit holder shank cylindrical portion and the lower portion of the bit block bore. As a result, the bit holder of the current invention stays snugly mounted in the bit block bore and prolongs the useful life of the bit holder and bit holder block assembly over that of the prior art. 
     Referring to  FIG. 6 , after the bit holder of the present invention is inserted into its bit block, the measured dimensions of the bit holder bore at J are 1.195±0.005 inches, at K is 1.195±0.005 inches, and at L is 1.195±0.005 inches. The axial distance between the back side  30  of the body flange  30  and each of the dimensions J, K and L given is ½ inch. The diameter of the bit holder bore at the distal end M of the shank is 1.195±0.005 inches. Since the diameter of the bit shank approximates 1.170 inches, in ordinary usage, the bit shank is able to rotate in the bit holder bore and yet be sufficiently closely fitted thereto to avoid shank slap or hammering that would tend to prematurely allow the bit assembly to fail in use. These dimensions and tolerances may vary depending on the manufacturer of the bit as well as the tolerances used for each part used in this assembly. 
     Referring to  FIG. 7 , a modification of the present invention generally at  112 , includes features identical to the first embodiment, with such features numbered the same as in the first embodiment with the addition of a  1  in front thereof. The only exception being the stepped, discontinuous flanged bore, generally indicated at  134 , with increasingly stepped portions  134   a ,  134   b , and  134   c  from the top  136   a  of slot  136  to the distal end  135  of the shank  112 . The modification  112  includes a front body portion  124  having an annular top surface  126 , a bevel portion  127 , a cylindrical tire portion  128 , and an annular back face  130 , all identical to the first embodiment  12 . 
     Thus, an improved bit holder has been shown and described which is suitable for use in applications wherein the shank of a bit is sufficiently long to extend substantially through the length of the bit holder bore, which may extend beyond the distal end of the bit holder bore to allow a C clip or other fastener to secure the bit in the bit assembly. Such bits are presently used in trenching operations and coal mining operations that provide for bit assemblies of differing sizes having bits with differing shank diameters. Therefore, the aim in the appended claims is to cover all such bit assemblies that come within the true spirit and scope of the present invention.