Abstract:
A tubular part is brazed into coaxial relationship with the bore of a second part having a counter bore for receiving the tubular part by providing a tubular sleeve within the bores of the two parts prior to brazing. After the braze material has cooled the tubular sleeve and any braze material around it is machined out of the bores. In a second embodiment a tubular part is brazed into a recess of the second part before a bore is drilled therein. After the parts are brazed together the bore is drilled through both the tubular part and the second part.

Description:
The present invention relates to an improved method for brazing tubular parts in coaxial relationship with the bore of another part where one end of the tubular part nests with respect to the end of a second part. 
     BACKGROUND OF THE INVENTION 
     Where a cylindrical member rotates within a complementary cylindrical bore, the useful life of the parts can be extended by providing a counter sink at one of the bore into which is inserted a tubular, hardened wear ring. For example, machines used to cut hard surfaces such as concrete and asphalt have a rotatable cutting wheel with a plurality of cutting tools mounted on the wheel which are moved against a hard surface to advance the cut. Each of the cutting tools has a cylindrical shank which is rotatably mounted in a complementary cylindrical aperture in a mounting block. As disclosed in my co-pending application, Ser. No. 09/121,726 filed Jul. 24, 1998, the useful life of a tool and the mounting block can be extended by providing a tungsten carbide tubular insert at the forward end of the aperture in the mounting block or holder. 
     It is customary to use a braze to retain parts, such as a tubular insert fitted in a countersink at the end of a cylindrical aperture. The brazing process consists of providing a ring of braze material which is fitted between the inner surface of the countersink and the outer surface of tubular sleeve. The ring of braze material prevents the hardened ring from becoming seated within the countersink until the braze material is heated and melts, after which the ring can be forced into the countersink until it has become seated. After the parts cool, a substantial portion of the braze material should remain between the inner surface of the countersink and the outer surface of the insert to retain the parts in the assembled relationship. I have found, however, that when the braze material melts and a tubular insert is forced into a countersink most of the liquefied braze material flows into the cylindrical bore leaving an insufficient amount of braze material to retain the parts in the assembled relationship. When a tungsten carbide insert is brazed into a countersink around the bore of a tool block, as described above, it has been found that the braze will fail when the tool is subjected to the forces required to cut hard material such as concrete or asphalt. 
     An improved method is therefore needed for brazing of tubular parts in nested relationship in which a greater portion of braze material would be retained between the parts. 
     SUMMARY OF THE INVENTION 
     Briefly, the present invention is embodied in a method of assembling a tubular part in coaxial relationship with the bore of another part where the end of the tubular part nests with respect to the second part. For the purposes of this discussion, two parts are considered to be nest when the end of a first part is complimentary in shape to the end of a second part such that the outer surface of the first part will fit in near proximity to the complementary surface of the second part with the spacing between the surfaces being sufficient for retaining a brazing material. A tubular sleeve having an outer diameter sized to slide within a countersink surrounding the end of a cylindrical bore is an example of parts which can be assembled in nested relationship. 
     In accordance with the present invention, to braze a tubular part in nested relationship to a second part having a coaxial bore therein, a ring of braze material is provided where the ring has an inner diameter at least equal to the inner diameter of the tubular part, and an outer diameter which is no greater than the outer diameter of the tubular part. The parts are arranged in coaxial relationship with the ring of braze material and a viscous flux positioned between the complementarily shaped surfaces. 
     A tubular sleeve made of a soft metal material having an outer diameter which is a little larger than the inner diameter of the cylindrical bore is thereafter press fitted into the bore of both the block or holder and slip fitted into the bore of the insert. The assembled parts are thereafter heated, causing the braze material to melt, after which the parts are moved into nested relationship. As the parts are moved into nested relationship, the braze material is retained between the parts by the tubular sleeve fitting into the coaxial tubular bores of the parts. 
     When the parts are thereafter cooled, causing the braze material to harden, the parts will be retained in the assembled relationship. Thereafter, the soft metal of the tubular sleeve can be removed in a machining process. Following the removal of the tubular sleeve, the parts will be retained together by the braze remaining between them. 
     In a second embodiment of the invention, a body part can be made having a bore therein and a tubular member brazed into a countersink around one end of the bore. In this embodiment a body part blank for which the bore has not been made therein is provided with an annular recess in the surface thereof. The recess has an outer surface complimentary in shape to the outer surface of the tubular member and the inner surface of the recess forms a cylindrical stub having a diameter slightly less than the inner diameter of the bore of the completed body part. An annular piece of braze material is placed in the recess and the tubular member is positioned over the braze material, and the parts are heated to melt the braze material. After the parts cool the tubular member will be brazed into the countersink. Thereafter the cylindrical stub can be drilled and bored out to form the bore of the body part after which the tubular member will be in a countersink surrounding the bore. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention will be had after a reading of the following detailed description taken in conjunction with the drawings where. 
     FIG. 1 is a cross sectional view of a mounting block having a cylindrical bore and a hardened metal wear ring into which a rotatable tool has been fitted; 
     FIG. 2 is an exploded view of the parts needed to braze the wear ring into the countersink surrounding the bore in the block; 
     FIG. 3 is a rear end view of the wear ring shown in FIG. 2; 
     FIG. 4 is a cross sectional view of the parts shown in FIG. 2, assembled prior to brazing; 
     FIG. 5 is a cross sectional view of the parts shown in FIG. 2 after the braze material has been melted; 
     FIG. 6 is a cross sectional view of the parts shown in FIG. 2 after the central sleeve has been machined out of the bore of the block; 
     FIG. 7 is an exploded cross sectional view of a partially manufactured tool body having a recess in the forward end thereof suitable for receiving a wear ring and a ring of braze material; 
     FIG. 8 shows the partially manufactured tool body shown in FIG. 7 with the wear ring brazed into the recess; and 
     FIG. 9 is a cross sectional view of the tool body shown in FIG. 7 after a bore has been drilled through the length thereof. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 3, a machine used to cut hardened material such as concrete has a plurality of mounting blocks  10  fitted around the circumference of wheel. Each mounting block  10  has a block body  12  with a cylindrical bore  14  extending from a forward surface  16  to a rear surface  18 . Fitted within a countersink  20  at the forward end of the bore  14  is a tubular tungsten carbide wear ring  22  having an outer surface  24  complementary in shape to the inner surface of the countersink  20  and a cylindrical bore  26  equal to or a little larger than the diameter of bore  14 , and a rear surface  25 . To provide room for braze material between the outer surface  24  of the wear ring and the inner surface of the countersink  20  a plurality of bumps  27  are spaced around the outer surface  24  of the wear ring  22 . Similarly, to space the rear surface  25  from the bottom surface of the countersink  20 , a second plurality of bumps  29  are spaced around the rear surface  25  of the wear ring  22 . 
     Fitted into the coaxial bores  14 ,  26  of the block body  12  and the wear ring  22  is a cylindrical mounting portion  28  of a tool  30  having a tapered forward cutting end  32 . The wear ring  22  prevents the cylindrical bore  14  from becoming enlarged as the tool  30  is forced against a hard surface such as concrete or asphalt, however the wear ring  22  will become dislodged from the countersink  20  unless it is adequately retained by braze material between the parts. 
     Referring to FIGS. 2 to  6 , in accordance with the present invention, to retain the wear ring  22  within the countersink  20  of the block body  12  a split ring  34  of soft steel is provided having an outer diameter sized to fit snuggly within the bore  14  of the block body  12  and more loosely in the bore  26  of the wear ring  22 . A ring of brazing material  36  having a inner diameter larger than the inner diameter of the bore  14  and an outer diameter which is less than the inner diameter of the countersink  20  is fitting around the split ring  34  between the block body  12  and the wear ring  22  as shown in FIG.  4 . Thereafter, the parts are subjected to heat until the braze ring  36  melts, after which the wear ring  22  can be seated into the countersink  20  as shown in FIG.  5 . 
     After the parts are allowed to cool, hardened braze material will extend between the inner surfaces of all the parts and, in particular, a substantial portion of the braze material will remain between the outer surface  24  of the wear ring  22  and the countersink  20 . Thereafter the split ring  34  and any braze material adhering between the outer surface of the split ring  34  and the inner surface of the bores  14 ,  26  can be machined away as shown in FIG. 6, and adequate braze material will remain between the parts to retain the parts in assembled relationship while the tool  30  is being used to cut a hardened surface, not shown. 
     In this embodiment the diameter of the bore  26  of the tungsten carbide wear ring  22  has been described as being a little larger than the diameter of the bore  14  of the block body  12  because tungsten carbide is brittle and is susceptible to becoming chipped while the split ring  34  is being machined out of the bore. By providing a bore  26  with a diameter which is a little larger than that of the block body  12 , the tungsten carbide will not become chipped while machining the split ring  34  away. It should be appreciated that the invention is usable to facilitate the brazing of many metal and even nonmetal materials, and whereas it is desireable that the bore of a tungsten carbide insert be a little larger than the diameter of the adjacent bore, a different relationship between the dementions of the parts may be desirable where different materials are involved. 
     It should be appreciated that the method of the present invention can be used to assemble any two parts which are to be retained in nested relationship with a coaxial bore of equal diameter extending between them. Specially, the method can be used to retain any two parts together where the parts having cylindrical bores of equal or nearly equal diameter and having complementary surfaces which fit together in nested relationship with bores thereof aligned in axial relationship to each other. 
     Referring to FIGS. 7 to  9 , a wear ring  40  having a cylindrical bore  42 , a frustoconical outer surface  44  and an annular forward and rear surfaces  46 ,  48  respectively may be brazed into a countersink  58  in the forward end of a tool body  52  to surround one end of a cylindrical bore  54  in accordance with the second embodiment of the invention. 
     In accordance with this embodiment, prior to forming the bore  54 , an annular recess  56  is formed in the forward end of the tool body  52 , the recess having an outer wall  58  complementary in shape to frustoconical outer surface  44  of the wear ring  40 . The annular recess  56  also leaves a cylindrical stub  60 , the diameter of which is equal to or a little smaller than the inner diameter of the bore  42  of the wear ring  40 . 
     As shown in FIG. 7, a ring of braze material  62  is placed within the recess  56  and around the stub  60 , and then the wear ring  40  is fitted within the recess  56  on top of the ring of braze material  62 . Preferably, the wear ring  40  has a plurality of protrusions  64 — 64  on the frustoconical surfaces thereof and has a second plurality of protrusions  65 — 65  on the rearward surface  48  on the outer surface thereof to space the surfaces of the ring  40  from the surface of the recess  56  in the tool body  52 . Heat is then applied to the parts causing the braze material  62  to melt and flow between the surfaces of the recess  56  and the surfaces of the ring  40  and after it has cooled, the ring  40  will be securely bonded into the recess  56  as shown in FIG.  8 . 
     After the ring  40  has been brazed into the recess  56  the tool body  52  can be placed into a lathe or other suitable tool for drilling and boring the bore  54  through the length of the tool body  52  to achieve the completed tool body shown in FIG.  9 . The outer surface of the recess  56  defines the outer wall of the countersink  50  of the completed tool body  52 . 
     While the invention has been described with respect to two embodiments, it will be appreciated that many modifications and variations may be made without departing from the true spirit and scope of the invention. It is therefore the intent of the appendent claims to cover such modifications and variations which fall within the true spirit and scope of the invention.