Abstract:
An improved brake drum and method for machining and balancing a brake drum are provided. The inner facing surface and the outer facing surface of the brake drum are machined. The inner and outer faces of the hub end of the brake drum are also machined. The machining is accomplished in a single operation that results in a radially balanced brake drum.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to brake drums and, in particular, to improved finished and balanced brake drums and a method of finishing and balancing such brake drums. 
   Most brake drums for trucks and similar heavy duty vehicles are comprised of a cast iron brake drum that is subsequently machined to near final tolerances. Typically, the machined brake drum has a slight imbalance that needs to be corrected. Accordingly, the brake drum is subjected to a balancing operation after machining. Such balancing can comprise welding correcting weights to an outer surface of the drum or removing part of the brake drum. 
   In particular, brake drums that have an integral raised squealer band extending from near an open end of the brake drum can be balanced by removing a portion of the squealer band. Such balancing by removing a portion of the squealer band to a constant or substantially constant depth is shown in U.S. Pat. No. 5,483,855. Another method of balancing is shown in U.S. Pat. No. 4,986,149, which discloses the removing of a crescent or wedge of material from the integral squealer band. It is desirable to provide a machined and balanced brake drum, and a method for machining and balancing such a brake drum. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an improved machined and balanced brake drum. 
   It is another object of the present invention to provide an improved method of machining and balancing a brake drum. 
   It is another object of the present invention to provide an improved method of machining and balancing a brake drum by machining the inner and outer radial surfaces of the brake drum. It is another object of the present invention to provide an improved method of machining and balancing a brake drum by machining the inner and outer surfaces of the hub end of the brake drum. 
   The improved method for balancing a brake drum in accordance with the present invention utilizes a cutting or milling machine or a lathe to machine the inner and outer radial surfaces of the brake drum. The inner and outer surfaces of the hub end of the brake drum can also be machined. This machining is accomplished in a single operation while the brake drum is held in a chuck assembly. The chuck assembly holds the brake drum at selected points around the outer radial edge of the open end of the brake drum. Such chuck assembly is designed to accurately hold the brake drum during machining to avoid eccentricity in the brake drum as it is rotated in the chuck assembly and exposed in the outer heads. Further, the brake drum is held in the chuck assembly in a manner that allows almost all of the outer radial surface of the brake drum to be machined. The result of the machining is to produce a brake drum that is balanced radially about the central radial axis of the brake drum. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a brake drum in accordance with the present invention; 
       FIG. 2  is an end view of the hub end of a brake drum in accordance with the present invention; 
       FIG. 3  is a perspective view of the open end of a brake drum in accordance with the present invention; 
       FIG. 4  is an end view of the open end of a brake drum in accordance with the present invention; 
       FIG. 5  is a perspective view of a brake drum held in a chuck assembly in accordance with the present invention; 
       FIG. 6  is a partial detailed side view of a brake drum held in a chuck assembly in accordance with the present invention; 
       FIG. 7  is a perspective view in partial cross section of a brake drum held in a chuck assembly with cutting heads also shown. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 1-4  of the drawings, a brake drum in accordance with an embodiment of the present invention is shown generally at  10 . It is seen that brake drum  10  is a generally cylindrical structure, having a circular open end  12  and a generally cylindrical braking section  14  extending from open end  12  to hub end  16 . Hub end  16  is seen to comprise a generally flat outer surface  21  and inner surface  23  that terminates by forming circular hub opening  20 . A plurality of wheel lug openings  22  are spaced around outer surface  21  of hub end  16 . 
   Transition section  18  is seen to extend from braking section  14  to outer surface  21  of hub end  16 . Braking section  14  itself is a generally cylindrical section extending at a nearly normal relation to open end  12 . However, it is also understood that a preferred embodiment of the present invention could have the outer surface  26  of braking section  14  extending at a slightly less than normal angle to open end  12 . 
   It should be understood that brake drum  10  is typically made of cast iron in a foundry operation. Accordingly, finishing machining operations are necessary. Such machining would include the finishing of an inner surface  25  of braking section  14  to assure a nearly perfect inner cylindrical surface. Such surfaces are necessary to accommodate the brake pads from the braking structure that brake drum  10  would surround. 
   Referring to  FIGS. 5 and 6 , unfinished brake drum  31  is shown to be a generally cylindrical structure. Brake drum  31  is usually made of iron in a foundry casting operation. Accordingly, outer facing surface  41  of hub end  42 , and outer radial surface  44  of brake drum  31  are shown to have an unfinished, as cast surface. Transition area  46  between hub end  42  and outer radial surface  44  is also shown to have an unfinished, as cast surface. Open end  37  of brake drum  31  faces downwardly. 
   It is understood that an inner facing surface (not shown) of hub end  42  also has an unfinished, as cast surface. Further, an inner radial surface (not shown) of brake drum  31  also has an unfinished, as cast surface. 
   Chuck assembly  30  is seen to comprise a cylindrical base section  33 . A plurality, usually four, of set up posts  32  are radially adjustably positioned in set-up post supports  52  which are themselves affixed to base section  33 . Set up posts  32  assist in the radically centered positioning of brake drum  31  on base section  33 . This assures that brake drum  31  is radially centered for concentric machining. 
   A plurality, usually four, of jaw clamps  34  are providing to grasp and hold brake drum  31  on base section  33 . Each jaw clamp  34  itself is held in a jaw clamp support  54  which is affixed to base section  33 . Such jaw clamp  34  is seen to be able to rotate through an arc in order to contact and hold brake drum  31  on base section  33 . Note that the contact between jaw clamp  34  and brake drum  31  is at preselected locations about radial edge  35  of an open end  37  of brake drum  31 . It is seen that the preselected contact locations are rather inobtrusive and leave almost all of the outer radial surface  44  of brake drum  31  open to machining by a cutting head. 
   Referring now to  FIG. 7 , brake drum  31  is seen to also include inner facing surface  43  of hub end  42 , inner radial surface  45  and inner transition surface  47  between inner facing surface  43  of hub end  42  and inner radial surface  45 . Lug openings  57  are also shown in hub end  42 . 
   Outer hub cutting head holder  62  is seen to support cutting head arm  64  and cutting head edge  66 . It can be seen that as brake drum  31  is rotated about its radial center axis  61  while held in chuck assembly  30 , outer hub cutting head holder  62  can be programmed to have cutting head edge  66  contact and machine the entire outer facing surface  41  of hub end  42 . 
   Inner hub cutting head holder  72  is seen to support cutting head arm  74  and cutting head edge  76 . It can be seen that as brake drum  31  is rotated about its radial center axis  61  while held in chuck assembly  30 , inner hub cutting head holder  72  can be programmed to have inner hub cutting head edge  76  contact and machine the entire inner facing surface  43  of hub end  42 . 
   Outer radial cutting head holder  82  is seen to support cutting head arm  84  and cutting head edge  86 . It can be seen that as brake drum  31  is rotated about its radial center axis  61  while held in chuck assembly  30 , outer radial cutting head edge  86  contact and machine virtually the entire outer radial surface  44  and outer transition section surface  46  of brake drum  31 . Only the small area from open end  37  to the bottom  87  of the outer radial surface  44  is not machined in this operation due to the need for jaw clamp  34  to contact brake drum  31  at preselected locations  35 . 
   Inner radial surface cutting head holder  92  is seen to support cutting head arm  94  and cutting head edge  96 . It can be seen that as brake drum  31  is rotated about its radial center axis  61  while held in chuck assembly  30 , inner radial cutting head holder  92  can be programmed to have inner radial cutting edge  96  contact and machine the entire inner radial surface  45  and inner transition surface  47 . 
   Accordingly, it is seen how brake drum  31  is machined and balanced in a single operation while held in chuck assembly  30 .