Abstract:
The milling machine tool holder or chuck is used to support a spindle on a chuck axis through which a crossbar is transversely and slideably mounted. First and second ends of the crossbar adjustably support a mirror and a dial indicator, respectively, so a machine operator can see a dial face of the dial indicator that is not visible and facing away from the operator. The crossbar has a bend which enables the dial indicator to be articulated to conveniently measure features near the chuck axis without interference between the spindle and the dial indicator. The dial indicator is securely mounted to a clamp adapter which is mounted to the second end. A wedge-shaped slot in the adapter is configured to receive and secure one of a plurality of sizes of dial indicators.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is related to an application filed on Jun. 17, 1997, Ser. No. 08/877,233, now abandoned, and priority to that application is claimed in this Continuation-in-Part application. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to tram bars and, more particularly, to a tram bar and a comparator used in the environment of a metal-cutting machine, such as a milling machine. In such a machine, a work piece is supported on a moveable table and a tool or cutter is rotatably supported in a collet or chuck. In accordance with the present invention, an improved tram bar is mounted in place of the cutting tool and allows a machine operator to inspect the workpiece with a minimum of time and effort. 
     BACKGROUND OF THE INVENTION 
     While operating on a workpiece using a conventional metal-cutting machine, such as a milling machine, where the workpiece is clamped to a work table, a dial indicator is periodically mounted in the chuck to gage its various surfaces. The operator must then maneuver the work table to move the workpiece into various desired positions with respect to his work station and to the milling machine axis. The quality or accuracy of the finished product depends on the accuracy with which the dial indicator is used to position the workpiece with respect to the machine axis. 
     The desired position of the workpiece is first approximated by the operator without the aid of any inspection device. A dial indicator is then inserted into the chuck and used according to known procedures to precisely adjust the location of the workpiece. An existing feature of the workpiece, such as a pilot hole, a slot or workpiece face, is typically used as a reference when positioning the workpiece. For instance, a workpiece may be centered on the machine axis using a dial indicator to compare sides of an existing hole to one another and the machine axis. The dial indicator may be mounted to a crossbar or one leg of an L-shaped bar to provide a convenient way of swinging the indicator through 360 degrees to compare different faces of the workpiece to one another at various radial distances from the machine axis. Prior art procedures, however, are cumbersome and time-consuming, regardless of whether the machine is a standard, manually-operated milling machine, or an automatic machine, such as a computer numeric control (CNC) machine. 
     The operator uses one hand to turn the machine tool chuck and the indicator mounted therein. The other hand is used to control movement of the machine table. With practice, both hands can be manipulated simultaneously to position the work table and rotate the chuck. However, during this procedure, when the dial indicator is rotated so that its dial face cannot be seen by the operator, the dial indicator cannot simply be rotated for viewing by the operator. The dial indicator must remain undisturbed in relation to the machining axis while measuring a workpiece. Instead, the operator will generally relinquish control of the work table and use one hand to manipulate a hand-held mirror so he can view the dial face while the other hand rotates the chuck. 
     When the dial indicator is mounted to a crossbar, which allows large workpieces to be measured, the dial indicator may physically interfere with the chuck when the indicator is positioned near the machine axis. This occurs when a feature such as a small hole is being measured and the indicator must be tilted in order to reach the feature near the axis. To avoid interference, the indicator is typically moved outwardly along the crossbar and tilted even further toward the machine axis so the small hole can be measured. By tilting the indicator, however, the dial face is left at an obscure angle and is for the operator difficult to view. 
     A clamp adapter is generally required to fasten the dial indicator to the tram bar. Prior art clamp adapters, however, are typically configured to receive only one size of dial indicator mount shaft, so each dial indicator must have its own clamp adapter. This results in increased cost to the operator, and increased time spent changing adapters. 
     A tram bar is needed which facilitates the use of various sizes of dial indicators, and reduces the number of manual tasks which the operator must perform while aligning and measuring a workpiece on a metal-forming machine. The present invention is drawn toward such an inspection device. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a tram bar that can effectively and easily measure features of a workpiece at any radial distance from, or angular relationship to, the machining axis within its reach. 
     Another object of the present invention is to provide a tram bar which can secure various sizes of indicator mount shafts. 
     Yet another object of the present invention is to eliminate the need for a hand-held mirror to view a dial indicator face resting in certain orientations. 
     In accordance with the present invention, a tram bar is provided in a metal-cutting machine, such as a milling machine, where a workpiece is supported on a work table, and wherein a cutting tool is normally provided on a machine axis in a rotatable support above the work table. In place of the cutting tool, the present invention contemplates inserting a spindle into the collet or chuck and providing a crossbar on the spindle so that the crossbar can be adjusted transversely of the machine axis. The crossbar has one end which is bent at an angle and provided with a clamp adapter. A dial indicator is adjustably secured to the clamp adapter so that the dial indicator can be articulated to rest in a plane generally parallel to the machine axis. A second end of the crossbar mounts a reflective mirror so that the dial indicator can be read when facing away from the operator. 
     One feature of the tram bar is the bent crossbar which allows the dial indicator to be articulated to an easily-viewed position when measuring a workpiece feature near the machine axis. 
     Another feature of the tram bar is a wedge-shaped receiving bore of the clamp adapter which mounts various sizes of indicator mount shafts. 
     An advantage of the present invention is that the tram bar can be used to easily measure a workpiece feature when the dial indicator faces away from the operator. 
    
    
     These and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of best mode embodiments thereof as illustrated in the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art tram bar shown schematically with a straight crossbar securing an indicator gage; 
     FIG. 2 is a perspective view of a tram bar according to the present invention showing a crossbar mounted to a spindle and securing a clamp adapter and a mirror; 
     FIG. 3 is an enlarged cross sectional view of the spindle and crossbar of FIG. 2 taken along the lines  3 — 3 ; 
     FIG. 4 is an enlarged elelvational view of the adapter illustrated in FIG. 2 shown with the crossbar and a clamp adapter cap disassembled; and 
     FIG. 5 is an enlarged elevational view of a clamping device taken along the lines  5 — 5  of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to a more detailed description of FIG. 1, the current state of the art in tram bars is illustrated as used on an end mill (not shown) and indicated generally by the numeral  10 . The mill has a work table  12  which can be moved in the direction of the arrows A and B as a cutting tool (not shown) is rotatably supported in the milling machine and moved vertically along machine axis  13  into contact with a workpiece  14  in the direction of arrow C, to form the workpiece  14  in accordance with known techniques. The cutting tool is removed, and in its place in the collet or chuck of the end mill, a spindle  16  is provided as shown. 
     The tram bar  10  includes a straight crossbar  18  mounted to the spindle  16 , and an indicator  19  having a single pivot  20 , a dial face  22  and a lock screw  23 . The lock screw  23  secures the crossbar  18  to the spindle  16 . Tram bar  10  is difficult to use when a feature of the workpiece  14  is being measured near the machine axis  13 , because the spindle  16  often interferes with the indicator  19  when the indicator is tilted to measure the feature. To avoid interference, the indicator  19  must be moved along the crossbar  18  in the direction of arrow D. However, when the indicator  18  is so moved, it must be angled such as indicated by the numeral  27 , leaving the dial face  22  in a difficult viewing position for operator  25 . 
     Another problem with tram bar  10  occurs when the spindle  16  is rotated to a position such that the indicator  19  is closer to the operator  25  than the machine axis  13 . In other words, in this position, the dial face  22  is facing predominantly away from, and not visible to, the operator  25 . To view the dial face  22 , the operator must use a hand held mirror or physically move himself to a position that affords a better view of the dial face  22 , resulting in wasted time and effort. 
     Referring to FIG. 2, a tram bar  50  according to the present invention includes a spindle  52 , an indicator gage  54 , a mirror  56 , a steel crossbar  58 , and a clamp adapter  60 . The spindle  52  has a spindle axis  53  and is configured to be received within a chuck (not shown) of a milling machine or other metal-cutting machine. The spindle  52  defines a cylindrical crossbar receiving bore  62  for mounting the crossbar  58  transversely to the spindle axis  53 . A knurled thumb screw  66  is threaded into the spindle  52  for engaging, and tightening against, the crossbar  58 . 
     The indicator gage  54  is well know in the art and includes a dial face  68 , an indicator tip  70 , and a single pivot  72  for articulating the indicator gage  54 . The indicator gage  54  has a mount shaft  73  which is secured to the adapter  60  in a manner which is described in detail below. 
     The mirror  56  has a reflective surface  75  and a polymeric mirror back  74  which is provided with, and secures, a supporting post  76 . The post  76  is preferably steel and is set in a mold as the back  74  is being injection molded. The post  76  is received in a clamping device  80  that frictionally holds the mirror  56  to the crossbar  58  in a desired angular relationship to both the spindle axis  53  and the crossbar  58 . The clamping device  80  allows manual adjustment of the mirror  56  (one time only) to allow the observer to view the dial face  68  by looking into the reflective surface  75 . 
     The crossbar  58  includes first and second ends  92 ,  94 , a straight first portion  96 , a second portion  98  that is angled or bent with respect to the first portion  96 , and a flat  97 . The flat  97 , which is better seen in FIG. 3 extends along the length of the crossbar, and has a width that allows effective engagement of the crossbar thumb screw  66  with the crossbar  58 . The flat  97  forms a plane which is perpendicular to a plane that includes the first and second portions of the crossbar  58 . 
     In use, the crossbar  58  is movable along the first portion  96 , and is secured to the spindle  52  by tightening the thumb screw  66  against the flat  97  of the crossbar  58 . It is contemplated that while the tram bar  50  will be used primarily by tightening the thumb screw  66  against the flat  97 , it is apparent that the crossbar  58  can be rotated and secured within the bore  62  in a different orientation. The alternative use allows articulation of the dial indicator to orientations which are not possible when the thumb screw  66  is tightened against the flat  97 . 
     Referring to FIG. 4, the clamp adapter  60  has an adapter axis  100  and includes a cylindrical outer surface  101  extending between proximate and distal ends  104 ,  106 . A cylindrical mount bore  108  is defined in the proximate end  104  and is slightly larger in diameter than a diameter  107  of the crossbar  58 . When the crossbar  58  is inserted into the mount bore  108 , a thumb screw  110  is used to secure the adapter  60  to the crossbar  58 . 
     The clamp adapter  60  has a threaded stud  112  extending distally from the distal end  106  along the adapter axis  100 , and includes threads  114 . An adapter cap  116  is configured to be installed over the stud  112  and includes a threaded bore  118  and a hollow end  122 . The threads  114  of stud  112  cooperate with threads of the threaded bore  118 . The hollow end  122  has an inner diameter  123  that is slightly larger than the outer diameter of the adapter  60 , and a flat surface  126  that engages and tightens against the shaft  73  when the cap  116  is threaded over the stud  112 . 
     A wedge-shaped slot  128  is defined transversely through the adapter axis  100  of the adapter  60 , and is configured to receive a plurality of differently sized indicator mount shafts  73 . By configuring the slot  128  to receive mount shafts having {fraction (5/32)}″, 3-16 , and ¼″ diameters, the adapter can be used with the most common dial indicator sizes. The slot  128  has walls  130  and a small slot end  132 , shaped generally in the form of a wedge. When the shaft  73  is inserted through the slot  128  and the adapter cap  116  threaded into the stud  112 , the flat surface  126  of the cap  116  forces the shaft  73  into the wedge, or slot end  132 . As illustrated, an indicator mount shaft  73 ′ having a small diameter is wedged further toward the small slot end  132  than an indicator mount shaft  73  with a large diameter. In either case, the indicator mount shaft is snugly secured in the adapter  60  between the flat surface  126  of the adapter cap  116  and walls  130  of the adapter  60 . 
     Referring to FIG. 5, the clamping device  80  secures the post  76  of the mirror  56  to the crossbar  58 , and includes opposed plates  131 ,  133 . Each of the plates  131 ,  133  has relieved areas  134  for contacting a spherically-shaped end  136  of the support post  76 , and a steel ball  137  at the end of the crossbar  58 . A conventional fastener such as a screw and nut  138 ,  140  are used to secure the opposed plates  131 ,  133  against the ball  137  and end  136 . 
     Obviously, if the dial face  68  in FIG. 2 is facing the operator, it can be viewed without use of the mirror  56 , but one important feature of the present invention resides in the fact that the operator  25  can use the mirror  56  to read the dial face  68  while using both hands to manipulate the work table and the machine chuck, even when the dial face  68  is facing away from the operator. 
     Variation to the above-described embodiment of my invention will occur to those skilled in the art. Although a vertical milling machine is shown, the invention can be adapted for use in a horizontal milling machine, and in other machines where a rotatable cutter is moved relative to a work piece to form a machined surface. Additionally, variations can be made to the adapter cap to enable a more secure attachment of the crossbar to the adapter, including fitting the flat surface  126  of the cap  116  with a pliable or resilient material to provide a locking effect for the adapter cap against the shaft  73 . Alternatively, the flat surface  126  can be treated or machined to improve its frictional engagement with the shaft  73 . Further, the adapter can be configured to receive additional configurations of dial indicators by changing the configuration of the wedge-shaped slot  128  accordingly. Still even further, the adapter cap can be attached to the adapter using methods other than threads, such as a quick release-type of locking lever or retainer.