Bit holders and bit blocks for road milling, mining and trenching equipment

0001This application is a divisional of Ser. No. 09/500,983 filed Feb. 15, 2000, now U.S. Pat. No. 6,371,567, which is a continuation in part of Ser. No. 09/273,690 filed on Mar. 22, 1999, now U.S. Pat. No. 6,364,420.

0002This invention relates generally to road surface removal or reclaimer-stabilizer equipment and mining equipment, and more particularly, to cutter bit holders and bit blocks used in such road milling, mining, and trenching equipment.

BACKGROUND OF THE INVENTION

0003Cutter bits are utilized in road, off-road and mining machinery on the perimeter and across the width of a rotary drum or on the outside of a continuous chain or the like where the bits are moved through an orbit which is intercepted by the face of the material being removed or recycled. Road milling equipment removes the defective surface of a road and smooths the top of all or selected portions of the road surface. The bits include a tip and a shank. The shank is received and may axially rotate in a bit holder which is secured onto a bit block that, in turn, is mounted on the drum. Each of the bits has a hardened tip, preferably made of tungsten carbide or such other hardened material that acts to remove a portion of the surface it contacts. By using a sufficient number of these bits around the outer surface of a rotating drum, a large amount of surface may be worked. Any surface being worked generally has a hardness which can be measured or anticipated prior to the removal operation. However, such road surfaces, or surfaces being removed have hardened irregularities running therethrough. The toughness or hardness of the irregularities may result in the breakage of the bits and holders as they are being run over such irregularities.

0004Additionally, a need has developed for providing ease of removability of bits in their bit holders, especially when the bit becomes worn and in need of replacement. U.S. Pat. No. 5,374,111 discloses an undercut flange at the bottom of a base of a bit that allows a pry bar to be wedged between that flange and the top of the bit block (no bit holder in this patent) to help remove a bit from a bit block. It would be desirable to provide a more efficient means for allowing the removal of a bit from a bit holder or a bit block.

0005Additionally, tightening a small fastener on the bottom of a bit holder to hold it in the bit block concentrates friction forces on a small area of the nut top face and the bottom of the bit block. It would be desirable to spread those friction forces over a larger area and avoid the use of a nut to retain the bit holder on the bit block.

0006Further, a need has developed for a truly quick-change type of bit holder that may easily and quickly be both inserted in the bit block and removed therefrom.

0007It is, therefore, an object of the present invention, generally stated, to provide an improved means for quickly mounting and/or removing a bit holder from its associated bit block.

0008Another object of the present invention is the provision of an improved means for mounting a bit holder in a bit block without the use of retaining nuts, clips or the like.

0009A further object of the invention is the provision of retaining a bit holder in a bit block by means of a resilient interference fit between the holder and the block.

0010Another object of the invention is the provision of an improved means for providing for breakage of inexpensive replaceable parts when road resurfacing equipment and mining equipment bits encounter very hard irregularities in the surface being milled or mined.

BRIEF DESCRIPTION OF THE DRAWINGS

0011The features of the present invention which are believed to be novel are set forth with particularity in the attached claims. The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which like numerals refer to like parts, and in which:

0012<figref idref="DRAWINGS">FIG. 1</figref> is a side elevational view of a bit block, bit holder and bit assembly constructed in accordance with the present invention;

0013<figref idref="DRAWINGS">FIG. 2</figref> is an exploded side elevational view of the assembly shown in <figref idref="DRAWINGS">FIG. 1</figref>;

0014<figref idref="DRAWINGS">FIG. 3</figref> is a side elevational view of a second embodiment of a bit holder constructed in accordance with the present invention;

0015<figref idref="DRAWINGS">FIG. 4</figref> is a top plan view of the bit holder shown in <figref idref="DRAWINGS">FIG. 3</figref>;

0016<figref idref="DRAWINGS">FIG. 5</figref> is a side elevational view of a second embodiment of a bit block for retaining the bit holder shown in <figref idref="DRAWINGS">FIGS. 3 and 4</figref>;

0017<figref idref="DRAWINGS">FIG. 6</figref> is a top plan view of the bit holder shown in <figref idref="DRAWINGS">FIG. 5</figref>;

0018<figref idref="DRAWINGS">FIG. 7</figref> is a side elevational view of the second embodiment including a bit, bit holder and bit block assembly;

0019<figref idref="DRAWINGS">FIG. 8</figref> is a bottom plan view of the second embodiment shown in <figref idref="DRAWINGS">FIG. 7</figref>;

0020<figref idref="DRAWINGS">FIG. 9</figref> is a side elevational view of a third embodiment of a bit holder constructed in accordance with the present invention.

0021<figref idref="DRAWINGS">FIG. 10</figref> is a top plan view of the bit holder shown in <figref idref="DRAWINGS">FIG. 9</figref>;

0022<figref idref="DRAWINGS">FIG. 11</figref> is a side elevational view of the third embodiment bit holder being manually hammered into its bit block;

0023<figref idref="DRAWINGS">FIG. 11a</figref> is a side elevational view of the third embodiment bit holder being manually hammered out of its bit block;

0024<figref idref="DRAWINGS">FIG. 12</figref> is a side elevational view of a fourth embodiment combination bit block/bit holder utilizing a long bolt and bottom nut to press fit the bit holder onto the bit block.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

0025Referring to <figref idref="DRAWINGS">FIGS. 1-2</figref>, a bit mounting assembly, generally indicated at <b>20</b>, constructed in accordance with the present invention, includes a bit, generally indicated at <b>21</b>, which is mounted on a bit holder, generally indicated at <b>22</b>, which, in turn, is secured on a bit block, generally indicated at <b>23</b>. The bit block <b>23</b> is one of a plurality of such blocks mounted around the outside of the generally circular drum (not shown) or on a movable chain or track (not shown).

0026Referring to <figref idref="DRAWINGS">FIG. 2</figref>, the bit, generally indicated at <b>21</b>, includes a forward end <b>24</b>, and a shank <b>25</b> or rear end thereof. The forward end <b>24</b> includes a hardened nose <b>26</b>, preferably made of tungsten carbide or a like material, a middle tapered portion <b>27</b> including a reduced diameter area <b>27</b>a and a bottom flange portion <b>28</b> which is made so as to rest on the bit holder, generally indicated at <b>22</b>. A spring steel retaining clip <b>30</b> is positioned over the shank <b>25</b> of bit <b>21</b> and is shaped so that when the bit <b>21</b> is inserted in the bit holder <b>22</b>, the retaining clip <b>30</b> will secure the bit therein while allowing it to rotate from external forces.

0027The bit holder <b>22</b>, constructed in accordance with the present invention, includes a generally flat annular leading surface <b>31</b> on which the rear side of the bit flange <b>28</b> rests when inserted therein. Adjacent the annular leading surface <b>31</b> is a middle or tapered portion <b>32</b> that ends in an enlarged flange portion <b>33</b>. In the preferred embodiment of the invention, a plurality of notches, flats or indents <b>32</b>a-d extend radially inwardly of the middle tapered portion from top surface <b>31</b> toward the flange <b>33</b>. The back side <b>34</b> of flange <b>33</b> is an annular flat surface which rests on the bit block <b>23</b> when mounted thereon, and includes one aspect of the present invention to be discussed below. Rearwardly adjacent the flange portion <b>33</b> is a reduced diameter cylindrical shank portion <b>35</b> and a shoulder portion <b>36</b> which may vary in length depending on its function, an undercut portion <b>37</b> is next to the shoulder portion <b>36</b>, and the bit holder terminates in a threaded portion <b>38</b> adjacent the distal end <b>44</b> thereof. If the nose <b>26</b> of bit <b>21</b> hits a hard discontinuity, bit <b>21</b> will fail first, the bit holder in this embodiment may be engineered to fail next across reduced diameter section <b>37</b>. The configuration allows the bit holder to tumble out of bit block bore <b>49</b> after failure.

0028Also shown in <figref idref="DRAWINGS">FIG. 2</figref> is a bore <b>40</b> that extends axially through bit holder <b>22</b> from a countersink <b>41</b> in communication with the front face <b>31</b>, through the tapered portion <b>32</b>, the flange portion <b>33</b> and a substantial portion of the shank <b>35</b>, <b>36</b> where it narrows at chamfer <b>42</b> to a smaller diameter bore <b>43</b>. Bore <b>43</b> extends the remainder of the bit holder to its distal end <b>44</b>, or it may be increased in diameter partly along its length to decrease the cross sectional reduced diameter section <b>37</b>, if desired. The length of the bore <b>40</b> is determined partly by the length of the shank <b>25</b> on bit <b>21</b>. The shank <b>25</b> fits within bore <b>40</b>, and is retained therein by the spring steel retainer <b>30</b>. If the bit <b>21</b> should break at reduced diameter portion <b>29</b> adjacent the bottom flanged portion <b>28</b>, a rod, punch, etc. (not shown) may be inserted into the bottom of the bore to push the shank out of the holder.

0029The bit block <b>23</b> consists of a base portion <b>45</b> that mounts to a drum, chain, or track (not shown) and an angled bit holder mounting portion <b>46</b> extending from the base <b>45</b> that includes a top face <b>47</b>, and a bottom recessed slot <b>48</b> which provides the opposing ends for a bore <b>49</b>, which may be tapered, and a reduced bridging portion <b>51</b> extending from a bottom of bore <b>49</b> to the recessed slot <b>48</b>. Bore <b>49</b> is sized to receive the cylindrical shank <b>35</b> of the bit holder <b>22</b> with the annular flat surface <b>34</b> on the bottom of the flange portion <b>33</b> resting on the top surface <b>47</b> of the bit block mounting portion <b>46</b>. In one important aspect of the present invention, the surface area of contact between flange bottom <b>34</b> and bit block top <b>47</b> is much greater than the surface area of contact between the top <b>52</b>a of nut <b>52</b> and nut contacting surface on slot <b>48</b> and will be discussed in greater detail below. The threaded portion <b>38</b> adjacent the distal end <b>44</b> of bit holder <b>22</b> extends through the reduced passageway <b>51</b> where a nut <b>52</b> may be threaded thereon by rotating the bit holder until its top surface <b>52</b>a engages the surface of the recessed slot <b>48</b> to retain the bit holder <b>22</b> on the bit block <b>23</b>.

0030Referring to <figref idref="DRAWINGS">FIG. 1</figref>, the distal end of a pneumatically operated chisel is shown in dotted line at <b>55</b>, inserted in one of the notches <b>32</b>C as more fully shown in <figref idref="DRAWINGS">FIGS. 3 and 4</figref>. The notches <b>32</b>a-<b>32</b>d, constructed in accordance with the present invention, allow for the quick removal of the bit <b>21</b> from the bit holder <b>22</b> by applying a force having a substantial axial component thereto to the bottom side of the bit flange <b>28</b>. In the preferred embodiments there may be two, three or four notches or indents <b>32</b>a-d (<figref idref="DRAWINGS">FIG. 2</figref>, <b>32</b>-d not shown) on the bit holder <b>22</b> positioned at 120 degree or 90 degree intervals, respectively, around the circumference thereof. Each notch may be straight vertically or slightly wider at surface <b>31</b> and narrows as the notch descends toward flange <b>33</b>. While the use of the punch <b>55</b> on one notch is usually sufficient to remove the bit, the punch may be utilized sequentially in differing notches to balance the axial force, if necessary, to move the bit <b>21</b> out of the bit holder <b>22</b>.

0031Referring to <figref idref="DRAWINGS">FIGS. 3-8</figref>, a second embodiment of the bit holder and bit block constructed in accordance with the present invention is shown and described. Beginning at <figref idref="DRAWINGS">FIG. 3</figref>, a second embodiment of the bit holder, generally indicated at <b>60</b>, is constructed to be a press fit into the bit block, generally indicated at <b>61</b>, shown in <figref idref="DRAWINGS">FIG. 5</figref>. The mounting of the bit holder <b>60</b> on the bit block <b>61</b> is accomplished without the aid of a retaining nut, such as shown at <b>52</b> in the first embodiment, a spring retaining clip or other fastening device utilized on the bottom of the bit block <b>61</b>.

0032Referring to <figref idref="DRAWINGS">FIGS. 3 and 4</figref>, similarly to bit holder <b>22</b>, the bit holder <b>60</b> has a flat annular leading surface <b>62</b>, a middle tapered portion <b>63</b> behind the flat annular leading surface <b>62</b> that also includes a pair of notches <b>64</b>-<b>65</b>, 120 degrees apart and having the same function as the notches <b>32</b>a-d in the first embodiment and an annular groove <b>63</b>a whose depth is calculated to insure that, in case of the bit hitting a hard discontinuity, the bit holder will break at groove <b>63</b>a rather than the bit block <b>61</b> separating at its weldment to the drum or chain. Additionally, the rear of the middle tapered portion <b>63</b> is an enlarged flange portion <b>66</b> including an annular flange backside <b>67</b> similar to that shown in the first embodiment <b>22</b>. A locator pin <b>69</b> extending from the flange back side <b>67</b> fits loosely into a clearance hole <b>69</b>a on bit block top surface <b>85</b> (<figref idref="DRAWINGS">FIG. 5</figref>) for limiting the rotation of holder <b>60</b> when mounted on the bit block <b>61</b>. If the bit holder breaks, the pin <b>69</b> falls out of hole <b>69</b>a and does not damage the bit block <b>61</b>. To the rear of the annular flange backside is the shank portion of the bit holder, generally indicated at <b>68</b>. An undercut <b>70</b> between the annular flange backside <b>67</b> and the shank portion <b>68</b> assures that stress points are avoided between the shank and the enlarged flange portion when the bit holder <b>60</b> is mounted in the bit block <b>61</b>. This undercut <b>70</b> also provides a breaking point if undercut <b>63</b>a is not used.

0033Flange <b>66</b> is annular in that a bore <b>71</b> runs axially through the bit holder in a more straight forward hollow cylindrical manner than the bore <b>40</b> which extends through the bit holder <b>22</b> of the first embodiment. The leading edge of bore <b>71</b> includes a countersink <b>72</b> adjacent the flat annular leading surface <b>62</b> of the bit holder to receive a similarly shaped shank portion <b>25</b> on the bit <b>21</b> shown in <figref idref="DRAWINGS">FIG. 2</figref>.

0034In an important aspect of the present invention, a slot <b>81</b> extends through the sidewall of the shank portion from the rear semi-annular face <b>77</b> to a rounded front slot termination <b>82</b>. An interference fit between the outside of tapered shank portion <b>73</b> and the like tapered bore <b>80</b> of the bit block <b>61</b> is greater than the standard interference or press fit possible if slot <b>81</b> was not in the shank portion. For example, a 1½ inch diameter shank without a slot would ordinarily have about 0.001-0.003 inch standard interference. With slot <b>81</b>, the same size shank may have about 0.005-0120.012 inch interference in the portion including the slot <b>81</b>. As the distal end <b>77</b> of the shank portion <b>68</b> is positioned in the tapered bore <b>80</b> of bit block <b>61</b>, the slot allows the now C-shaped portion of the shank to contract its outer diameter radially to ease the insertion of the bit holder in the bit block bore <b>80</b>. This slotted portion of the shank <b>81</b> allows the C-shaped portion of the shank to act as a very strong radial spring, similarly to a hollow spring steel roll pin. The portion of shank <b>68</b> forward of slot <b>82</b> provides a 360 degree radial interference fit with the bit block bore <b>80</b>, and may be greater than, equal to, or less than an interference fit at the portion of the shank at <b>101</b>. The length of the slot <b>81</b> with respect to the length of the shank portion <b>68</b> may be varied depending upon the application proposed for the bit, bit holder and bit block assembly in order to optimize the operation of same. The slot <b>81</b> may, when desired, extend all the way to the rear annular flange back side <b>67</b> of the front tapered shank portion of the bit holder <b>60</b>. The longer the slot, the less spring action force of shank <b>68</b>. A smaller width slot provides a greater spring force. The taper for the shank <b>73</b> and bore <b>80</b> is preferably 1 degree on each side, but may be more or less, such as 2 to 4 degrees per side or ¼ to ¾ degree per side, if desired. The smaller taper such as 1 degree has a longer length of interference fit engagement and produces more radial pressure for the same axial force exerted upon it than a two degree taper for the same press fit values.

0035Referring to <figref idref="DRAWINGS">FIGS. 5 and 6</figref>, bit block <b>61</b> is similar to bit block <b>23</b> with the exception that the bit block bore <b>80</b> is tapered on the order of about 1 to 4 degrees per side or 2 to 8 degrees of included angle, unlike straight bore <b>49</b>. A second locator pin <b>89</b> may be mounted in a bore <b>89</b>a to extend slightly into the bore <b>80</b> of the bit block <b>61</b>. In use pin <b>89</b> is about ½ inch in diameter and extends into slot <b>81</b> of the bit holder slot about 3/16 inch to keep the bit holder <b>60</b> from rotating in the bit block <b>61</b> and to align the slot <b>81</b> in the bit block. A clearance hole <b>69</b>a on top flat surface <b>85</b> allows the locator pin in <b>69</b> (<figref idref="DRAWINGS">FIG. 3</figref>) to be positioned loosely therein. An annular slot <b>87</b> is formed across the bottom portion of the bit block tail surface <b>88</b>, otherwise, bit block <b>61</b> is very similar to bit block <b>23</b> in construction.

0036Referring to <figref idref="DRAWINGS">FIGS. 7 and 8</figref>, the bit <b>21</b> and the second embodiments of the bit holder <b>60</b> and bit block <b>61</b> are shown in assembled condition with the exception of the modification in the bit block <b>61</b> to provide a slot <b>85</b> positioned in the outer portion of bit block <b>61</b> to more easily allow the insertion of tools in the rear of the bit block <b>61</b> to drive the bit <b>21</b> from the bit holder <b>60</b>.

0037<figref idref="DRAWINGS">FIG. 8</figref> shows the bottom of the assembly including the flat planar mounting pad <b>86</b> which mounts to the rotating wheel or moving track on which the assembly is positioned. As one can see from <figref idref="DRAWINGS">FIGS. 7 and 8</figref> there is no bolt, retaining pin or other retaining means to maintain the bit holder in the bit block. Additionally, force may be applied to the distal end surface <b>77</b> of the bit holder <b>60</b> to drive the bit holder out of the bit block <b>61</b>. As with the first embodiment of the present invention, the notch <b>65</b> in the front tapered portion of the bit holder <b>60</b> allows a chisel (not shown) or other such device to apply force on the back side-of the bottom flanged portion <b>28</b> of bit <b>21</b> to drive the bit out of the bit holder. Again, no bolts, retaining pins, retaining rings or the like are necessary between the bit holder <b>60</b> and the bit block <b>61</b>.

0038Referring to <figref idref="DRAWINGS">FIGS. 9 and 10</figref>, a third embodiment of the bit holder of the present invention, generally indicated at <b>90</b>, is similar to the second embodiment bit holder <b>60</b> with two exceptions to be discussed below. The forward portion of the bit holder <b>90</b> including the leading flat annular surface <b>91</b>, a cylindrical front collar portion <b>92</b>, the middle tapered portion <b>93</b> and the enlarged flange portion <b>94</b> perform similar functions to the forward portion of the bit holder of the second embodiment <b>60</b>. Also, a pair of notches <b>95</b>, <b>96</b> perform an identical function to the notches <b>64</b>, <b>65</b> of the second embodiment. The forward portion of the bit holder of the third embodiment is somewhat more compact axially than the second embodiment. Another difference in the third embodiment of the present invention is the construction of the shank portion, generally indicated at <b>97</b>.

0039The shank portion <b>100</b> is also tapered as is the shank portion <b>68</b> in <figref idref="DRAWINGS">FIG. 3</figref> with approximately 1 degree of taper per side as shown at T₁in <figref idref="DRAWINGS">FIG. 9</figref>. The shank portion also includes an undercut section <b>98</b> between the back side <b>94</b>b of the enlarged flange portion and the shank portion <b>97</b> to avoid sharp areas of stress when mounting the bit holder <b>90</b> in a bit block such as that shown at <b>61</b>. This portion of the shank could also be designed in either embodiment using a radius at <b>98</b> and providing sufficient relief at countersink <b>120</b> (<figref idref="DRAWINGS">FIG. 5</figref>) in bit block <b>61</b>. In an important aspect of the third embodiment of the present invention, the tapered outermost surface of the shank is divided into a front tapered portion <b>100</b> and a rear tapered portion <b>101</b>. In this third embodiment <b>90</b>, shoulder <b>102</b> is formed between the front tapered portion <b>100</b> and the rear tapered portion <b>101</b>. The distal portion of the shank <b>77</b> (<figref idref="DRAWINGS">FIG. 7</figref>) is constructed identically to that of the second embodiment with a rear face <b>103</b> a distal chamfer <b>104</b> a cylindrical tail portion <b>105</b>, a transition chamfer <b>106</b> and rear tapered portion <b>101</b>. Likewise, the bit holder of the third embodiment may include a central bore <b>107</b> therethrough and a slotted portion <b>108</b> (<figref idref="DRAWINGS">FIG. 10</figref>) similar to the slot <b>81</b> (<figref idref="DRAWINGS">FIG. 3</figref>) of the second embodiment <b>60</b>. Slot <b>108</b> allows for a greater interference fit between rear taper <b>101</b> and bit block bore <b>80</b> (<figref idref="DRAWINGS">FIG. 5</figref>). In the third embodiment <b>90</b>, the shoulder <b>102</b> reduces the interference fit on opposing sides from about 0.009 at <b>101</b> to about 0.002 inch between the frontal portion of slot <b>108</b> and undercut <b>98</b>. The rear taper <b>101</b> and the front taper <b>100</b> are preferably identical, in this embodiment 1 degree. However, these tapers can vary as discussed previously above.

0040Identical smaller tapers give a longer taper contact at each end of the shank. If the angle of the taper at portion <b>100</b> is greater than the angle of the taper at portion <b>101</b>, the axial length of contact between taper portion <b>100</b> and bore <b>80</b> of block <b>61</b> will be lessened. Also, a convex surface may be substituted for the tapers <b>100</b> and <b>101</b> with the result being less surface contact between the holder shank <b>100</b>, <b>101</b> and block bore <b>80</b>.

0041The shoulder <b>102</b> assures that the portion of the front taper <b>100</b> immediately adjacent the shoulder <b>102</b> does not touch the bore <b>80</b> of the bit block <b>61</b> as the bit holder is driven into the bit block. As the bit holder is further driven into the bit block and the diameter of front taper <b>100</b> increases until interference contact is made adjacent the forward end of taper <b>100</b> where the 100 percent circumferential surface is located The slot <b>108</b> decreases in width mostly in press fit zone <b>101</b> to allow the bit holder to be driven into the bit block. The position at which the front taper <b>100</b> achieves an interference fit with the bit block bore <b>80</b> is approximately that position shown in <figref idref="DRAWINGS">FIG. 11</figref>, i.e., about ¼ to ⅝ inch. The interference fit between the taper portions <b>100</b>-<b>101</b> and bore <b>80</b> maintain the bit holder in fixed mounted position in bore <b>80</b>. The use of pin <b>89</b> which extends through bore <b>89</b>a into the bore <b>80</b> (and slot <b>108</b> when the holder is inserted in the block) assures that proper alignment and minimal rotation occurs between the holder <b>90</b> and the bit block <b>61</b>. However, when using greater interference fit on taper portion <b>101</b>, no pin may be required in certain applications.

0042Referring to <figref idref="DRAWINGS">FIGS. 11 and 11a</figref>, a means for mounting the bit holders of the present invention in their respective bit blocks is shown at <figref idref="DRAWINGS">FIG. 11</figref>, and a means for demounting or removing the bit holders from their respective bit blocks is shown at <figref idref="DRAWINGS">FIG. 11a</figref>. In <figref idref="DRAWINGS">FIG. 11</figref>, the bit holder <b>90</b> or bit holder <b>60</b> are substantially driven into the bit block <b>61</b> with the use of a first drive pin, generally indicated at <b>105</b>, that includes an elongate shank portion <b>106</b> having a slip fitting cylindrical distal end <b>120</b> which loosely fits in the bore <b>107</b> (<figref idref="DRAWINGS">FIG. 10</figref>) of the bit holder. A reduced shaft portion <b>121</b> may be positioned mediate the distal slip fitting cylindrical portion <b>120</b> and an enlarged cylindrical portion stop member <b>122</b> including an annular face <b>123</b> thereon adapted to matingly engage the front annular flat surface <b>91</b> of the bit holder. An enlarged head portion <b>117</b> absorbs the blows of a hammer <b>118</b>, which strikes the same to drive the press fit shank portion <b>97</b> (<figref idref="DRAWINGS">FIG. 9</figref>) of the bit holder <b>90</b> into the bore <b>80</b> of the bit block <b>61</b>. The slip fitting distal cylindrical portion <b>120</b> and the annular face <b>123</b> of the drive pin <b>105</b> assures that the bit holder <b>90</b> will be accurately positioned-to drive same into the bore <b>80</b> of the bit block <b>61</b> without harming any potential annular inserts, such as shown at <b>163</b> in <figref idref="DRAWINGS">FIG. 12</figref> positioned at the upper flat annular surfaces of either the bit holder or the bit block. The hardened inserts, being more brittle than the softer ductile material of the remainder of the bit block <b>61</b> and bit holder <b>90</b> will be more likely to be damaged during insertion of the bit holder <b>90</b> in the bit block <b>61</b> if a non-close fitting drive pin were used rather than the preferred embodiment drive pin <b>105</b>.

0043Referring to <figref idref="DRAWINGS">FIG. 11a</figref>, a second drive pin, generally indicated at <b>130</b>, is utilized to remove or drive out the bit holder <b>90</b>, or bit holder <b>60</b> of the present invention from the bit block <b>61</b>. Drive pin <b>130</b> includes an enlarged head portion <b>131</b> for accepting the blows of the hammer <b>118</b> previously mentioned. The shaft portion <b>132</b> includes a slightly reduced diameter distal end <b>133</b> having a semispherical tip <b>134</b> of larger diameter than the bore <b>107</b> of the bit holder <b>90</b>.

0044In operation, the semispherical distal tip <b>134</b> is <b>10</b> positioned on the central bore <b>107</b> of the bit holder <b>90</b> at a countersink <b>77</b>a (<figref idref="DRAWINGS">FIG. 7</figref>) on its rearward distal end <b>103</b>. Since the semispherical end <b>134</b> is larger in diameter than the central bore <b>107</b>, it allows the drive pin <b>130</b> to be positioned in other than a coaxial position with the central bore <b>107</b> of the bit holder <b>90</b>. Countersink <b>77</b>a provides for additional engagement between the distal end of the tool <b>130</b> and the bit holder. This provides positioning the drive pin around combinations of bit, bit holders and bit blocks mounted adjacent the bit holder that is being removed from its respective bit block. The hammer <b>118</b> striking the enlarged end <b>131</b> of the drive pin provides an axially oriented component of force to drive the press fit bit holder <b>90</b> outwardly of the bore <b>80</b> of the bit block <b>61</b>. When needed an anti-seize grease is applied to the mating parts for easier assembly and disassembly.

0045Referring to <figref idref="DRAWINGS">FIG. 12</figref>, a second means of inserting the bit holder <b>160</b> into the bit block <b>61</b> is shown. This second insertion means includes a threaded bolt, generally indicated at <b>110</b>, including a threaded portion <b>111</b>, which extends through the bore <b>180</b> of the bit holder <b>160</b> and out the distal end thereof. A specialized nut <b>112</b> is threaded on the threaded distal end of the bolt <b>110</b> until contact is made with the rear of the bit block. Then, nut <b>112</b> is retained in a non-rotating position by a wrench or by means between the nut and the back side slot <b>115</b> of the bit block <b>61</b>. Then the hexagonal front bolt portion <b>113</b> of the bolt is rotated with the threads <b>111</b> engaging the internal threads on the nut <b>112</b> such that the hex head <b>113</b> drives the front face <b>162</b> of the bit holder, and thus the remainder of the bit holder <b>160</b>, into the bit block <b>61</b> until the back side annular flange <b>67</b> (<figref idref="DRAWINGS">FIG. 3</figref>) seats on the front face <b>85</b> of the bit block <b>61</b>. The front face <b>162</b> of bit holder <b>160</b> includes a hardened frustoconical tungsten carbide insert <b>163</b> disclosed in U.S. patent application Ser. No. 09/121,726.

0046While four embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from the true spirit and scope of the present invention. It is the intent of the appended claims to cover all such changes and modifications which fall within the true spirit and scope of the invention.