Abstract:
A straddle-cutting device for machining a pair of parallel surfaces on a rotating workpiece in a single cut as the cutting tool is advanced over the workpiece. 
     Apparatus is provided for biasing the cutting tools using a stack of spring washers and a pneumatic power cylinder.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
   This invention is related to straddle-cutters, that is, apparatus for cutting two parallel surfaces on opposite sides of a workpiece in a single cut. Two side cutters spaced at a precise distance, machine the two sides of the workpiece simultaneously. For example, brake rotors are machined in this manner. Usually commercial forms of such a device use hydraulic power for moving the cutters into and out of position. 
   The broad purpose of the present invention is to provide an improved straddle-cutting apparatus using pneumatic power, and a combination of Belleville springs. 
   Currently industry uses hydraulic fluid/air over hydraulic fluids to actuate piston/cylinders to extend and retract a straddle-cutting tool. Filters, valves, and piping fittings are required to move the fluids and produce the necessary pressures to activate hydraulic piston and cylinders. As the cutting force is applied to the workpiece, a reactionary force in the other direction acts upon the cutters. Liquids have the nature to drift or collapse under applied pressures. Consistencies for dimensional control may be compromised in quality for statistical process controls. 
   Hydraulic vessels run higher-pressure levels and response times than mechanical advantage devices. Hydraulics used for this application also requires programmed timing for the response. 
   The preferred embodiment of the invention employs a pair of cutting tools spaced on opposite sides of the cutting position of a workpiece. At least one of the cutting tools is movable toward one face of the workpiece for a cutting motion and then retracted by a pneumatic cylinder. An axially movable shaft moves the cutting tool. The pneumatic cylinder moves a lever to move the shaft to retract the tool. A stack of Belleville washers, mounted around the shaft, return the shaft to extend the cutting tool. 
   The preferred straddle-cutter provides several advantages over the prior art. It provides a cleaner work environment, and reduces areas for potential hydraulic leaks by eliminating the use of hydraulic oil. The preferred apparatus requires fewer tubular piping and connections, fewer pressure fittings and reduces service calls. The preferred apparatus functions in a factory using industry standard air pressure. No new pressures or factory installations are required. The manufacturer sets the standard of air pressure utilized at the cutter by stamping the requirements directly into the housing. 
   The mechanical advantage is more reliable because direct mechanical contacts between the internal mechanical devices are used. There are no internal leaks or slippage. A manufacturing advantage exists because reliable product quality is available through reliable management and reduction of the equipment down time. The product holds product dimensions, harmonic surfaces and run-outs to industry standards. Presetting the tooling lends to industry, “lean manufacturing”. 
   All external components and details attached to the cutter housing are industry standard items, allowing the user to comparatively shop for replacements, and to develop its own inventories of spare parts based upon usage. The products internal design focuses against the various backlashes, and deflections in loadings produced in manufacturing by engineering their details and assemblies to directly access the linear and axial movements associated with resultant forces. 
   Further advantages are that the preferred straddle-cutter provides the ability to consistently return the cutting tool to the material-removal position. Programming and response time are eliminated, allowing for more product manufactured per work shift. The cutter can maintain a constant force despite changes in a mechanical system resulting from wear, relaxation or thermal change. 
   At rest, the cutting tool is in the closed, material-removal position. Proper product dimensional control is given to the machinist in an external, manually controlled turning cartridge capable of maintaining relatively small positional tolerances. The cartridge can be adjusted rather than the entire tool. This rest position may also be gaged for final dimensional manufacturing size by the finished product. 
   When clean air is supplied, the tool opens to a clearance position unable to cut or remove material. This enables the cutter housing holding the cutters to retract back to a home position without causing damage to the finished product surface. At this point, the finished product is unloaded and the next unfinished product is loaded. 
   Still further objects and advantages of the invention will become readily apparently to those skilled in the art to which the invention pertains, upon reference to the following detailed description. 

   
     DESCRIPTION OF THE DRAWINGS 
     The description refers to the accompanying drawings in which like reference characters refer to like parts throughout the several views and in which: 
       FIG. 1  is a sectional view of a straddle-cutting apparatus illustrating the preferred embodiment of the invention; 
       FIG. 2  is a top view showing the lever; 
       FIG. 3  is a view of the shaft separated from the remainder of the device; 
       FIG. 3A  is a sectional view as seen along lines  3 A— 3 A of  FIG. 3 ; 
       FIG. 4  is a view of a typical tool holder; and 
       FIG. 5  is a view of the two major components of a positive locking coupling (PLC) separated, one from the other. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the drawings,  FIG. 1  illustrates a preferred straddle-cutting apparatus  10  which comprises a base plate  12  carried on a turret, not shown. A pair of cutting tools  14  and  16  are mounted on the base plate, on opposite sides of the cutting position of a metal workpiece  18  having parallel surfaces which are to be machined. Power means, not shown, rotates the workpiece on a spindle  20  in one direction of arrow  22 . The two cutting tools are advanced over the workpiece in the direction of arrow  24  for material removal and then returned to their initial position (home) in the direction of arrow  26 . 
   Lower cutting tool  14  is illustrated in  FIG. 4 . The upper cutting tool  16  is similar to cutting tool  14 . Cutting tool  14  comprises a tool holder  28  mounted on the base plate, and a clamp  30  connected by fastener means  32  to the tool holder. Clamp  30  locks a cutting insert  34  in a recess in the tool holder. The tool holder  28  has an adjusting screw  38 . 
   Referring to  FIG. 1 , tool holder  28  is slidably mounted on lower jaw  39 . Adjusting screw  38  engages an abutment  40  on lower jaw  39  to adjust the position of the tool holder in a direction parallel to the surface of the workpiece, and with respect to upper cutting tool  16 . Lower jaw  39  is slidably mounted on base plate  12  for motion perpendicular to the face of the workpiece. 
   A shaft  44  is mounted in a housing  46  that is attached to the base plate. The lower threaded end of the shaft is connected to the housing by a nut  48 . A key  50  locks the shaft to the lower jaw so that the shaft can be moved up and down with the lower jaw in the direction of arrows  52  and  54 . The upper end  56  of the shaft extends above housing  46 . 
   Referring to  FIGS. 1 and 2 , a first class lever  58  is supported by a pivot pin  60  (fulcrum) so that the lever can pivot around the pivot pin with one lever end  62  engaging the upper end of the shaft. The opposite end  64  of the lever engages a piston rod  66  which forms a part of a pneumatic power cylinder  68 . Power cylinder  68  is mounted in an opening  69  in the housing and is adapted to extend or retract piston rod  66  in either an upper direction  70  to push lever  62  away from the cylinder, or in a lower direction  72  to permit lever end  64  to move toward the cylinder. 
   The arrangement is such that when the piston rod is extended, the lever pushes shaft  44  downwardly together with the lower jaw. When the piston rod is retracted, the lever then permits shaft  44  to slide upwardly in the direction of arrow  54 . Power cylinder  68  is connected to a source of air under pressure  74  through a conduit  76 . 
   When the piston rod is extended from the power cylinder, shaft  64  moves down, as viewed in  FIG. 1 , and carries cutting tool  14  away from cutting tool  16  to open the gap between the two tools. 
   Referring to  FIG. 3 , shaft  44  has an integral annular plate  78  disposed in chamber  80  in the housing. The plate moves up and down with the shaft. Chamber  80  has a lower annular abutment  82 . Two sets of spring washers, preferably Belleville washers  84  and  86 , are mounted in the chamber around an enlarged portion  88  of the shaft. Each set of Belleville washers comprise a pair of washers mounted edge-to-edge, and back-to-back with a companion pair of washers. The stack of Belleville washers opposes the downward axial pressure of the lever on shaft end  56  separating the lower cutting tool from the upper cutting tool. When piston rod  66  is retracted, the Belleville washers bias the shaft together with lower jaw  42  upwardly, thereby re-engaging the lower cutting tool with the upper cutting tool. 
   The linear motion of piston rod  66 , shaft  44  and cutting tool  14  are all perpendicular to the lower face of workpiece  18 . The range of motion of the shaft is in the nature of millimeters so that the Belleville washers provide a sufficient force for raising the lever a very small distance. 
   The number of Belleville washers employed depends upon the particular application to which the apparatus is being used. The Belleville washers may provide a force of 1600 pounds on the shaft. 
   In some cases, the shaft may tend to drift from its desired rotated position. Referring to  FIGS. 1 and 5 , a positive locking coupling  90  returns the shaft to its initial position when the shaft is released from the downward pressure of the lever. As is well known, a positive locking coupling comprises two coupling components  92  and  94 , having an annular array of teeth  96  and  98 . Coupling component  92  has a central opening  100  that suitably receives shaft  44 . Coupling component  92  is attached to the housing by suitable fasteners, not shown. 
   Coupling component  94  is attached to the shaft to move as a unit with the shaft and the lower jaw when the piston rod is extended, to separate teeth  98  from teeth  96 . When the piston rod is retracted, the shaft then rises with coupling component  94  to mesh teeth  98  with teeth  96  to return the shaft to its original rotated position. 
   A pin  101  is mounted in the housing and received in an opening  102  in coupling component  92 . The pin limits any swinging or rotating of coupling component  94 . 
   Upper cutting tool is mounted on an upper jaw  103  and attached to a turret, not shown, in such a manner that the turret moves the upper cutting tool toward or away from the upper face of the workpiece during the course of a machining cycle. 
   In use, the gap between cutting tool  14  and cutting tool  16  is adjusted to take a certain amount of material from either or both the upper face and the lower face of the workpiece. Cutting tool  14  can remove a certain depth of material on the lower face of the workpiece, while upper cutting tool removes a different amount of material from the opposite face. 
   The user then rotates the workpiece and advances the straddle-cutter in the direction of arrow  24  to a final cutting position on the workpiece. When the machining has been completed, the straddle-cutter opens and is returned to its initial (home) position in the direction of arrow  26 .