Abstract:
A holder ( 20 ) for a cutting insert ( 12 ), which includes a head ( 22 ) with a pocket ( 24 ) for holding the cutting insert and a bar device ( 26 ) for supporting the head, allows the use of a removable head for a miniature head and bar device that fits into a small hole in a workpiece, and allows rapid and easy replacement of the head. The head has a front part ( 42 ) of small height for holding the cutting insert and has a taller rear part ( 40 ) of the same height as the bar device. The head rear part has a screw-receiving hole ( 56 ) that extends at a downward-rearward incline (A) into a corresponding threaded hole ( 62 ) at the front of the bar device. The head and bar device respectively have a recess ( 70 ) and a projection ( 74 ) that lie around the screw-receiving holes and that align the head and bar device. A coolant passageway system ( 92 ) in the bar device provides coolant for both right and left hand heads.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Small holes drilled into a workpiece can be machined to form a precision finished surface on the hole walls, by rotating the workpiece on a lathe while a cutting insert is advanced within the hole. The cutting insert is mounted in a pocket of a holder head. It is often desirable to detachably mount the holder head on a holder bar device so the head can be replaced. In prior systems, holder heads on bar devices of ⅝th inch and larger diameters are held by a multiple screw/multiple serration system. In that system, precision mounting of the head on the bar device is achieved by miniature screws and multiple serrations on each part that interfit. For bar diameters of under ⅝th inch the cost to manufacture a screw and serration configuration makes such system impractical. In prior art systems for bar diameters under ⅝th inch the holder device is simply brazed to the bar device in a one piece construction.  
         [0002]     It would be desirable if a machining apparatus were available that could be practically built on smaller shanks such as those of ⅜ths inch diameter, and that was of simpler and lower cost construction. If the holder head could be easily replaced on the bar device, a holder head could be used that had an insert-holding pocket that could receive a particular type of cutting insert, and a damaged head could be replaced on a holder device without removal from the machine tool.  
       SUMMARY OF THE INVENTION  
       [0003]     In accordance with one embodiment of the invention, a cutting insert holder is provided, of the type that has a head with a pocket that holds the cutting insert, wherein the head is easily detachable from a bar device in a construction that is of low cost and that allows the holder to fit into a small workpiece hole. The head has a front part that holds the cutting insert and that is of small height, and has a rear part that is of a greater height about equal to that of the bar device. A screw extends through a hole in the head rear part and through a threaded hole in the front of the bar device, to hold the head securely on the bar device. A recess and projection are provided, one on the rear of the head and the other on the front of the bar device, to precisely locate the head on the bar device. The screw extends within the recess and projection, so widely-spaced locating surfaces are provided on the recess and projection.  
         [0004]     The screw-receiving holes in the head and bar device, preferably extend at a downward-rearward incline. The front surface of the head rear part preferably extends at a downward-forward incline, and the screw has a tapered head that fits into a tapered end of the inclined hole in the head rear part.  
         [0005]     The bar device includes a rigid bar of tungsten carbide and a carbon steel mount brazed to the front end of the bar. A coolant bore extends through the middle of the bar along its axis. The mount forms a passage system that allows the coolant to flow to either side of the mount. The head has a coolant passage at the same side of the head in which the insert-holding pocket lies. This allows coolant to be directed parallel to the axis, but at the cutting insert.  
         [0006]     The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a partial rear isometric view of a cutting apparatus of the invention, shown with a front portion lying in a hole of workpiece, the workpiece being shown in phantom lines.  
         [0008]      FIG. 2  is a left side elevation view of the cutting apparatus of  FIG. 1 , with portions shown in hidden lines.  
         [0009]      FIG. 3  is a plan view of the cutting apparatus of  FIG. 2   
         [0010]      FIG. 4  is an exploded side elevation view, with a portion shown in section, of the cutting apparatus of  FIG. 2 , with only a portion of the bar being shown.  
         [0011]      FIG. 5  is a view taken on line  5 - 5  of  FIG. 4 .  
         [0012]      FIG. 6  is a top view of the head and mount of  FIG. 3 , and shows in phantom lines a head with a left hand cutting insert. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]      FIG. 1  shows a cutting apparatus  10  of the present invention, which includes a cutting insert  12  that has been advanced forwardly F so it lies in a hole  14  of a workpiece  16 . The workpiece is mounted on a lathe spindle that turns the workpiece. The insert is held by a holder  20  that includes a head  22  with a pocket  24  that receives the cutting insert. The holder also includes a bar device  26  formed by a shank or bar  30  and a mount  32  that forms a front part of the bar device and that is fixed to the front end of the bar. The head  22  is detachably mounted on the mount  32 . In the prior art, the smallest practical cutting apparatus with detachable head could fit only into a hole of ⅝th inch or greater diameter. A smaller cutting apparatus could be made by fixing the head to the bar device by brazing, but then the head is not detachable from the bar device.  
         [0014]      FIG. 2  shows that the head  22  has a rear part  40  with a height in a vertical direction V that is about the same as the height of the bar device  26 . The head also has a head front part  42  of about half the height of the rear part. This results in the upper surface  46  of the head front part lying at about the proper height for the top of the insert  12 . The rod  30 , mount  32 , and rear part  40  of the head all have a cross-section of primarily cylindrical shape (closer to a cylinder than square) of the same height, at least for smaller sizes such as to fit in holes of under one inch diameter.  
         [0015]     In accordance with the present invention, the head  22 , shown in  FIG. 4 , is detachably fastened to the mount  32  by a head screw  50 . The head screw extends at a downward D and rearward R incline as seen in a side view, and lies on the centerline or axis  51  of the head and of the bar device as seen in a top view. The particular incline angle A is 30° from the horizontal. The head screw has a screw head, or screw front part  52 , and a screw shank  53 . The screw shank has a shank front part  54  that lies in a screw-receiving hole  56  in the head. The screw has a threaded shank rear part  60  that lies in threadable engagement with a threaded screw-receiving hole  62  in the mount. The two screw-receiving holes  56 ,  62  can be considered to be a screw-receiving orifice  68 . The rear part  46  of the head has a front surface  64  that extends from the top  65  of the head rear part and that is inclined at an angle of more than 10° from the vertical with angle B being 60° from the horizontal. As a result, the screw centerline  66  extends at about a right angle to the inclined surface  64 . The circumference of the screw head  52  is tapered, preferably with a small taper angle C, and the rear of the screw-receiving hole is similarly tapered. Applicant uses conical surfaces with a taper angle C of less than that of the most common taper angle of 82.5° for such “finishing” screws. The small taper angle C which is preferably less than 70° and which is shown as 60°, results is the rear end of the screw head  52  having a smaller diameter to fit into the small space available for it on the inclined surface  64 .  
         [0016]     The head  22  is precisely located on the mount  32  by a recess  70  in the rear mating end  72  of the head that closely receives a projection  74  at the front mating end  75  of the mount.  FIG. 5  shows that the recess, whose recess walls are indicated at  80 , is of larger lateral L, or horizontal width E and larger vertical height G than the screw-receiving hole  62  in the mount (and than the screw-receiving hole in the head). The head screw has a shank diameter H that is more than one-fourth the width or diameter J of the cylindrical mount and of the head rear end, so the screw can withstand large forces encountered in machining. The fact that the locating surfaces of the recess and projection  70 ,  74  have greater widths and heights than such a large diameter head screw, results in the ability to provide precision locating of the head on the mount.  
         [0017]     The projection  74  shown in  FIG. 5  has long vertical surfaces  82 ,  84  on opposite sides of the screw-receiving hole, which fit closely between vertical walls of the recess, with a clearance between them no more than about one mil (one mil equals one-thousandth of an inch) (“about” means no more than 1.5 mil). This assures high precision in horizontal locating of the head on the mount. The projection has 45° inclined top and bottom surfaces  76  that locate the head on the mount with moderate precision (clearance of about 3 mils) because precision locating in the vertical direction is not as important as precision locating in the horizontal direction.  
         [0018]     The recess and projection each have a length K ( FIG. 4 ) along the axis  51  that is about one-eighth the height of the head rear part. Such small length of less than 25% of the bar device height G is desirable to assure that high torque encountered in machining is not applied to the projection walls to bend them.  
         [0019]     The bar or shank  30  is usually constructed of tungsten carbide to assure high rigidity. The mount  32  is constructed of carbon steel which can be machined far more easily than tungsten carbide. The head is also constructed of carbon steel. The bar  30  is formed with a coolant bore  90  that preferably extends along the bar axis  51 . Applicant uses the mount to direct the coolant around the screw holes and around the locating recess and projection, and also to better distribute coolant to where it is needed. As shown in  FIG. 6 , the mount has a passageway system  92  which includes a middle part  94  lying on the axis  51 , a pair of sidewardly-extending passage parts  102 ,  104  that extend from the middle part, and a pair of longitudinally-extending parts  110 , 112  that extend primarily parallel to the axis. These parts of the passage system are drilled in the mount, with a plug of material (not shown) at  114  to close passage part  102 . The head rear end has one opening  116 , which is aligned with the leftward passage part  112 . The head rear part has a coolant conduit  120  that extends forwardly from the opening  116  and that has a front end  122  that lies directly behind the cutting insert and that directs coolant along the upper surface of the head front part to the upper surface of the cutting insert  12 . This efficiently uses the coolant because the coolant is directed at the location where cutting occurs. If a head is used with a pocket and cutting insert located on the right side of the head then such head will have a passage aligned with the right side passage part  110 .  
         [0020]     Applicant&#39;s head can be removed and a new one installed, in much less time than for prior detachable heads. This allows a machinist to remove a cutting insert that has a worn or broken cutting edge, by replacing the head with another one containing a cutting insert with a fresh cutting edge. The small insert screw  130  ( FIG. 3 ) that holds the cutting insert to the head is often inconvenient to reach, and the small screw is commonly fumbled when removing and reinstalling it. As a result, such screws often drop into a space where they cannot be recovered. It is much easier to replace the entire head because the head screw  50  that holds the head in place is much larger (e.g. the head screw  50  may be of 3 mm diameter while the insert screw  130  is of about 1.5 mm diameter). Removal of the entire head allows the machinist to check the pocket that holds the cutting insert for possible deformation, and allows removal of the cutting insert to reinstall it with a new cutting edge in position to cut or to replace it, in a convenient location where there is light and a fumbled small screw will drop onto a table top.  
         [0021]     The shank  53  ( FIG. 6 ) of the head screw lies on the axis  51  of the holder  20 , but extends at a downward-rearward incline. The threaded shank rear part  60  ( FIG. 4 ) of the head screw, threadably engages the threaded hole  62  in the mount both above and below the axis  51  for optimum fastening. It would be desirable if the head screw extended along the axis  51 , but the head front part  42  is in the way. The inclined head screw is a good compromise.  FIG. 6  also shows, in phantom lines, a head  22 A with a pocket  24 A for holding a left hand cutting insert  12 A, and with a coolant conduit front end  122 A for directing coolant at the cutting edge of the left hand cutting insert.  
         [0022]     Although terms such as “top”, “down”, etc. have been used to describe the invention as it is illustrated, it should be understood that the holder can be used in any orientation.  
         [0023]     Thus, the invention provides a machining apparatus of the type wherein the head is detachable from the bar device, which can be manufactured in smaller sizes than previously, which allows detachment and reattachment more rapidly and with greater ease, which provides a stronger connection and one that assure greater head-locating precision, and which provides better coolant direction. The head is attached to the bar device by a head screw that extends into a rear head part and that extends at an incline into the front part of the bar device. A screw-receiving orifice is shown which extends at a rearward-downward incline and with the screw head bearing against the head rear part. However, it is possible to use an upward-rearward incline and/or have the screw head bear against the mount. The head and bar device form a mating recess and projection that both lie around the screw and that precisely locate the head on the bar device. The rear part of the head preferably has an inclined surface that extends at a downward-forward incline, and the screw has a tapered head that lies in a front end of the screw-receiving hole in the head. The bar device directs coolant along two laterally-spaced passage parts, and the head has a conduit that directs coolant from a passage part at one side of the head to a location at the top of the cutting insert.  
         [0024]     Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.