Abstract:
The present invention is a housing retrofit assembly for a milling machine or the like, including a quick adjusting stop nut for selective sliding coarse adjustment and rotational precision fine adjustment for rotatable engagement with a threaded rod or shaft in close tolerances, which provides stable precision engagement with the shaft, and which provides a positive locking mechanism. A unique lighting assembly is also disclosed which moves with the machine head for illuminating the milling cutter or the workpiece.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part of U.S. patent application Ser. No. 10/653,482, filed Sep. 2, 2003 now U.S. Pat. No. 6,789,986, which claims priority from U.S. patent application Ser. No. 10/222,252, filed Aug. 16, 2002, now U.S. Pat. No. 6,612,790, and claims the benefit of U.S. Provisional Application No. 60/312,969, filed Aug. 16, 2001. 

   FIELD OF THE INVENTION 
   The present invention relates generally to attachments for machine tools. The invention concerns a housing assembly that is adapted and retrofitted for use with vertical milling machines to measure the vertical travel, or milling depth, of the quill mechanism. More particularly, the invention concerns a stop mechanism for engagement with a threaded rod, and a control mechanism for the quill. 
   BACKGROUND 
   Vertical milling machines are known in the art and a number of different types of milling machines are commercially available. By way of example, Bridgeport® and RF Rong Fu® produce various models of milling machines. These commercially available milling machines are generally classified into two main divisions, vertical and horizontal. In the horizontal milling machines, the cutter is horizontally mounted to a spindle and moves in a horizontal manner. Similarly, in a vertical milling machine, the cutter is vertically disposed and moves in a vertical fashion. 
   A conventional vertical milling machine generally includes a table on which a workpiece can be supported, and a quill that supports a tool or cutter for movement toward and away from the table for milling the workpiece. Typically, the table is adjustable within the horizontal plane from side to side and from front to back relative to the quill. Although many milling machines are manual, in the sense that adjustment of the table and movement of the quill is manually achieved, improvements in the art have been made for fully automated machines. These automated machines provide some advantages over manual machines, however, they are considerably more expensive for users. Moreover, they lack the versatility of manual machines. 
   In addition to the above, many of the manual, vertical milling machines commercially available provide an already attached manual measuring apparatus for determining the vertical travel, or milling depth, of the quill. By way of example, RF Rong Fu® milling machines provide a plastic assembly located on the face of the machine. The assembly comprises a housing attached to the milling machine and a moveable indicator attached to a quill shaft stop bar. The housing further has a rectangular hole which is centrally located thereon and a measurement scale surrounding the hole. As the quill is lowered and raised the indicator points to a corresponding measurement on the measurement scale, thereby informing a user of the approximate vertical movement or depth. 
   A disadvantage of the current measuring devices provided in milling machines is that they do not provide precise measurements. Typically, the units of measure on the devices are not small enough and one&#39;s ability to properly bore holes and mill workpieces is restricted. An example of an industry that thus is restricted is the steel industry, in which machined parts must be milled to precise tolerances. The measuring units currently provided simply do not and cannot accurately measure pieces to ensure that certain hole depths meet those tolerances. Thus, a need exists for an apparatus which provides a precise measurement of the depth or vertical movement of a quill. 
   Currently, there exist some measuring devices which accurately determine the vertical movement of the quill. However, for various reasons, these devices are ineffective to accomplish the objects stated herein. For example, the Mitutoyo Corporation manufactures the Digimatic Quill Kit for vertical Bridgeport® milling machines and Bridgeport® type machines. The Quill Kit essentially is a retrofitted housing comprising a main scale, a digital display indicator attached to the front surface of the main scale, a rear support plate secured to the rear of the indicator, thereby securing the indicator to the main scale, a tapped hole mounting bracket which is attached to the scale, a base, a scale stop bar that is mounted to the rear plate, a scale stop bracket and a plurality of screws and washers. The Quill Kit unit is attached to a milling machine by first retracting the spindle of the machine and removing the quill wheel. Vernier scale screws of the milling machine are removed and the base is placed over the vernier scale. The vernier screws are replaced and the mounting bracket is attached to the base. The scale is attached to the mounting bracket by the scale stop bracket. 
   A disadvantage of the Quill Kit is that it is only useful for Bridgeport® type machines. The device simply cannot be used on other types of milling machines, such as the RF Rong Fu® models. Moreover, the Quill Kit is comprised of many unnecessary components. As such, it is expensive to manufacture. 
   Stops and guides for use on drilling, depth milling and other similar machinery are known, as are quick release nuts which provide for selective sliding or threading motion with respect to a threaded shaft. Guthrie U.S. Pat. No. 4,693,656 describes such devices. Current stops, as shown by Guthrie, have a spring which presses against the end of the release nut, causing the stop to remain in place. However, such arrangement is not sufficiently tight to prevent movement of the stop on the threaded shaft or rod. 
   Thus, it is clear that a need exists for an inexpensive, stop which can hold be tightly when desired, and which can be provide both coarse and fine adjustments, and which is simple and versatile, and readily retrofit for use with vertical milling machines, and which is readily removable. 
   SUMMARY OF THE INVENTION 
   The present invention is a quick adjusting stop nut for selective sliding coarse adjustment and rotational precision fine adjustment for rotatable engagement with a threaded rod or shaft in close tolerances, which provides stable precision engagement with the shaft, and which provides a positive locking mechanism. 
   The present invention is particularly useful with a retrofit apparatus for vertical milling machines which generally comprises a mounting cover, a main scale, an indicator, a rear plate, a plurality of hat clips, a plurality of screws, a quill stop bar, a set screw, a quill stop mount and a graduated rod. The main scale is slidably attached to the rear of the indicator. The rear plate is connected to the rear surface of the indicator by a plurality of screws with the scale displaced therebetween. The mounting cover of the present invention has a generally rectangular configuration. Further, the mounting cover has a generally elongated rectangular aperture, substantially and centrally located therein. The length of the aperture extends along the length of the mounting cover face. The scale, indicator, and rear plate are secured to the face of the mounting cover by a plurality of hat clips. The components are secured so that the indicator is fixed within the aperture of the mounting cover and slidably moves in concert with the quill. 
   Attachment of the assembly to the quill stop bar and quill stop mount is accomplished by screwing the rear plate to the quill stop bar and inserting the quill stop bar into an aperture in the quill stop mount. A graduated rod is provided for connection to the quill stop mount, thereby allowing the slide support and scale to slidably move up and down. The entire assembly is then fixed to a milling machine by a plurality of screws which are matingly inserted into a plurality of corresponding receiving holes located on the milling machine and the left and right sides of the mounting cover. 
   In an alternative embodiment, the invented retrofit generally comprises a mounting cover, a main scale, an indicator, a slide support, a clamp mount, a plurality of hat clips, a plurality of screws, a quill stop bar, a quill stop mount and a graduated rod. The main scale is slidably attached to the rear of the indicator. The slide support bracket is connected to the rear surface of the scale by a plurality of hat clips and screws which partially cover the ends of the front surface of the scale. The mounting cover of the present invention has a generally rectangular configuration. Further, the mounting cover has a generally rectangular aperture, having a substantially similar configuration as the indicator, located at the bottom end of its face. The scale, indicator, and slide support are secured to the mounting cover by a clamp mount, which is disposed between the indicator and the slide support. The components are secured so that the indicator is fixed within the aperture of the mounting cover. 
   Attachment of the assembly to the quill stop bar and quill stop mount of the alternative embodiment is accomplished by screwing the slide support to the quill stop bar and inserting the quill stop bar into an aperture in the quill stop mount. A graduated rod is provided for connection to the quill stop mount, thereby allowing the slide support and scale to slidably move up and down. The entire assembly is then fixed to a milling machine by a plurality of screws which are matingly inserted into a plurality of corresponding receiving holes located on the milling machine and the left and right sides of the mounting cover. 
   In another alternative embodiment of the present invention, the retrofit comprises a mounting cover, a main scale, an indicator, a rear plate, a hat clip clamp mount, a quill stop, a mount and a quill shaft. The aperture of the mounting cover is of a corresponding size to the indicator. The main scale is slidably mounted to the indicator by the rear plate. The indicator and scale are attached to the mounting cover by the clamp mount. In addition, the indicator and scale are fixed to the quill shaft and quill stop at the mount. Subsequently, the entire assembly is joined to the milling machine by a plurality of screws which connect the two by a plurality of corresponding holes located on the milling machine and the left and right sides of the mounting cover. 
   In a further embodiment of the present invention, a second generally elongated aperture is present along side the first aperture. The second aperture is of a shorter length and runs parallel to the first aperture. Displaced within the second aperture is a hard stop block having a T-bolt configuration. The hard stop block has an additional lock lever which, when engaged allows a user to set the block along the second aperture at a predetermined point. In operation, the user moves the hard stop block to a desired location on the second aperture and locks it in place. Once the quill is extended, the rear plate contacts the hard stop block and resists further extension. This feature allows the user to mill multiple workpieces at a consistent depth. 
   Another embodiment is shown in  FIGS. 24–29 , which provides for one or more light assemblies to be focused on the milling head or the workpiece. 
   OBJECTS OF THE INVENTION 
   Accordingly, it as a principal object of the present invention to provide a stop nut for milling machines which accurately and tightly holds against vertical movement of a quill during operation. 
   A further, and more particular, object of the invention is to provide a stop nut for a threaded rod that can be adapted and retrofitted to various machines. 
   Another object of the invention is to provide a stop nut assembly which allows measuring the precise vertical movement of a quill or other device during operation, while holding tightly to prevent movement during operation. 
   Another object of the invention is to provide lighting means movable with the quill head adjacent the milling cutter. 
   A further object of the invention is to provide lighting means which illuminates the workpiece, and allows for replacement of bulbs. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects will become more readily apparent by referring to the following detailed description and the appended drawings in which: 
       FIG. 1  is a front view of a conventional vertical milling machine, but including a circuit breaker switch. 
       FIG. 2  is a fragmentary view of the milling machine shown in  FIG. 1 . 
       FIG. 3  is an isometric exploded view of a housing assembly of the present invention; 
       FIG. 4  is a side view of the invented housing assembly of  FIG. 3 ; 
       FIG. 5  is a front view of the invented housing assembly of  FIG. 3 ; 
       FIG. 6  is an exploded isometric view of an alternative embodiment of the housing assembly of  FIG. 3 ; 
       FIG. 7  is a side view of the alternative embodiment of the housing assembly of  FIG. 6 ; 
       FIG. 8  is a front view of the alternative embodiment of the housing assembly of  FIG. 6 ; 
       FIG. 9  is an exploded isometric view of another alternative embodiment of the housing assembly of  FIG. 3 ; 
       FIG. 10  is a side view of the alternative embodiment of the housing assembly of  FIG. 9 ; 
       FIG. 11  is a front view of the alternative embodiment of the housing assembly of  FIG. 9 . 
       FIG. 12  is a side view of a further alternative embodiment of the housing assembly of  FIG. 3 . 
       FIG. 13  is a fragmentary side view of the alternative embodiment of the housing assembly of  FIG. 12 . 
       FIG. 14  is an exploded isometric view of the alternative embodiment of the housing assembly of  FIG. 12 . 
       FIG. 15  is a cross-sectional view of the invented stop nut assembly. 
       FIG. 16  is a partially cutaway view of the stop nut assembly of  FIG. 15 . 
       FIG. 17  is a cross-sectional view of the stop assembly showing a stop mechanism. 
       FIG. 18  is a schematic right side view of the stop assembly of  FIG. 15 . 
       FIG. 19  is a cross-sectional view of the invented stop assembly of  FIG. 15  showing an alternative spring biasing means. 
       FIG. 20  is a left side view of the spring of  FIG. 19 . 
       FIG. 21  is shows the offsets of the two bores in the plunger. 
       FIG. 22  is a partial view of a milling machine showing the stop nut assembly installed thereon. 
       FIG. 23  is a partially sectioned side view of  FIG. 22 . 
       FIG. 24  is a partially cutaway front view of a milling machine showing another alternative embodiment of a retrofit assembly. 
       FIG. 25  is side view of the embodiment of  FIG. 24 . 
       FIG. 26  is a side view of a milling machine incorporating the embodiment of  FIGS. 24 and 25  therein. 
       FIG. 27  is a cross-sectional view of an alternative light assembly, which is readily adaptable to a quill in accordance with the invention. 
       FIG. 28  is a front view of a light switch assembly mounted on a quill for activating one or more lights of a light assembly. 
       FIG. 29  is a cross sectional view of the light switch assembly taken along line A—A. 
   

   DETAILED DESCRIPTION 
   Referring now to the drawings, a conventional vertical milling machine  100  is shown in  FIGS. 1 and 2 , and generally includes a frame presenting a table  112  and a quill head  114  overlying the table  112 , and a quill  116  supported on the head  114  for rotation and for relative shiftable movement along a central longitudinal axis thereof toward and away from the table  112  between retracted and extended positions. 
   The frame includes an upstanding column  118  which supports the quill  116  and head  114 , and a knuckle (not shown) supported on the column  118  for pivotal movement about a transverse, horizontally extending shaft (not shown). The knuckle is secured in place relative to the column  118  by a plurality of bolts which can be loosened to enable orientation of the knuckle to be adjusted about the shaft. The head  114 , in turn, is mounted on the knuckle for pivotal movement about a horizontal axis that is perpendicular to the axis of the shaft. Angular adjustment of the quill  116  about the X and Y axes can be achieved in order to orient the quill  116  at any desired angle relative to the table  112 . 
   A motor  120  is mounted on the head  114  for driving rotation of the quill  116 , and a manual feed lever  122  is connected to the quill  116  through a rack and pinion quill feed transmission so that when the lever  112  is shifted, the quill  116  is moved between the retracted and extended positions. The motor  120  is connected to the quill  116  through a suitable transmission arrangement for automatically extending the quill  116  when the transmission is engaged. The feed transmission arrangement includes a quill feed engagement control lever  124  that protrudes from a boss on the right side of the quill head  114  for permitting an operator to engage and disengage the feed transmission, as desired. A cover is normally held in place over the quill head  114  that can be removed to allow access to the transmission components within the head  114 . 
   The feed transmission of the motor  120  includes a feed kick-out mechanism for disconnecting the quill  116  from the feed drive of the motor  120  when the quill  116  has been extended by a distance preset by the user. The feed kick-out mechanism includes a depth stop screw (not shown) supported between the quill head  114 , a depth stop block received around a stop screw (not shown) and the quill  116 . A travel stop ring  126  is threaded onto the stop screw for adjustment along the length thereof. When the quill feed engagement control lever  124  is moved to the engaged position, the quill  116  is moved automatically toward the extended position by the motor  120  and the depth stop block travels along the depth stop screw until the block engages the travel stop ring  126 . The force of the stop block against the ring  126  trips the engagement lever  124  and the feed transmission between the motor  120  and the quill  116  is disconnected. 
   A scale box  128  is centrally mounted over the quill head  114  with a manual scale  130  disposed therein to allow a machinist to gauge the depth of the quill  114 , and to set the position of the travel stop ring  126  so that drive to the quill  114  is disconnected at the desired depth. The scale box  128  has a generally elongated rectangular aperture for receiving the scale  130 . The scale box  128  is fixed to the milling machine  100  at predetermined connection points  132 . The connection points  132  are preferably threaded holes located in the milling machine  100  and are adapted to receive screws which secure the scale box  128  in place. 
   The vertical milling machine thus far described is a conventional knee mill, e.g. of the type manufactured by RongFu Corporation. Similar machines are made by several other manufacturers around the world, such as Bridgeport®, and the housing retrofit of the present invention can be adapted for use on any of these conventional machines without departing from the scope of the present invention.  FIGS. 1 and 2  show an improvement to the conventional machines whereby a two-way or three-way circuit breaker switch  70  is provided for activating and deactivating the machine. 
     FIGS. 3–5  show a preferred embodiment of the invented retrofit apparatus  10 . The retrofit apparatus  10  generally comprises a mounting cover or housing  12  having a generally rectangular face configuration, a main scale  14 , an indicator  16 , a rear indicator plate  18 , a plurality of hat clips  20 , a plurality of screws  22 , a cylindrical quill stop bar  24 , a quill stop mount  26  which is adapted to receive the quill stop bar  24 , a set screw  28 , and a cylindrical graduated rod  30 . 
   The included indicator  16  is a digital displacement indicator. An example of the indicator is such as that produced by the Mitutoyo Corporation for indicating the depth of holes, slots and countersinks. The indicator  16  generally includes an indicator head having a digital readout  32  and a plurality of control buttons  34 . The indicator  16  further includes an attachment means whereby it can be secured to the main scale  14  by attachment screws (not shown). While the Mitutoyo Corporation device is stated as an exemplary model which may be used in the present invention, other suitable digital displacement indicators may be used. 
   The mounting cover  12  is preferably made of aluminum or steel and has a left side  36 , a right side  38 , a face  40 , a top end  42  and a bottom end  44 . The mounting cover  12  may be made of other suitable materials which can accomplish the objects stated herein. Further, the face  40  of the mounting cover  12  has a generally rectangular aperture  46  located therein. The aperture  46  of the face  40  has a width corresponding to that of the indicator  16 . However, the length of the aperture  46  substantially extends to the top and bottom ends  42  and  44  of the mounting cover  12 , thereby allowing the indicator  16  to slidably move along the scale  14 . Located on the mounting cover&#39;s left and right sides,  36  and  38  respectively, are attachment notches  48  for attaching the retrofit apparatus  10  to a milling machine  100 . 
   The main scale  14  has a generally elongated rectangular configuration and is formed so that the indicator  16  can be slidably mounted thereto. The scale  14  is secured to the outer surface of face  40  of the mounting cover  12  by the plurality of hat clips  20 . Further still, the indicator  16  is slidably mounted to the scale  14  by the rear plate  18 . Attached to the rear plate  18  at one end is the quill stop bar  24  which is matingly engaged with the quill stop mount  26  at its opposing end. The quill stop mount  26  is adapted to receive the cylindrical graduated rod  30 . 
   After the scale  14  and indicator  16  are attached to the mounting cover  12 , they are attached to the quill stop bar  24  via the rear plate  18 . The quill stop bar  24  is, in turn, matingly connected to the quill stop mount  26  at the upper end of its front surface. The quill stop bar  24  is secured in place by the set screw  28  which is received in an angular cavity located on the stop bar  24 . The graduated rod  30  is also matingly connected to the quill stop mount  26  at its bottom surface. The retrofit apparatus  10  is fixed to the milling machine  100  by a plurality of screws (not shown) which connect the two by predetermined connection points  132  located on the milling machine  100  and the left and right sides,  36  and  38 , of the mounting cover  12 . A mounting slot  72  may be provided in mounting cover  12  at any convenient or desired location for receiving an mounting a light  74  thereto. The light is preferably a flexible extended light or flexible neck light, so that it can be directed toward the work. When the quill moves up or down, light  74  moves with it. 
   An alternative light assembly  220  is shown in  FIG. 27 . The light assembly has a power source shown as a flexible wire  224  in a flexible tubing (known as a “flex-stay” tubing) which is connected to a switch  226  in a switch assembly  222  which is mounted on the quill  116 . The light assembly  220  has an interior housing  228  containing a bulb receptacle  230  for accommodating one or more light emitting diodes  232  (LEDs), referred to hereinafter as LEDs or bulbs. An exterior housing  234  surrounds the interior housing and the bulb receptacle. A parabolic reflector  236  is advantageously positioned within the exterior housing for directing the light from the bulb. The end  240  of the exterior housing from the which the light is emitted has a tempered glass cover  242  to protect a lens, the cover being resistant to scratching. A focusing lens  244  is mounted within the housing  234 , beneath and spaced from the cover. The lens  244  is preferably glass or plastic, but could be any other desired material, such as quartz or mica. A rubber or neoprene separator  246  between the lens and the cover acts as a washer or seal to waterproof the light housing, and prevent water, oil, or any other liquid from entering the light assembly. The cover  242  is held in place against the seal  246  by a retainer  248  such as a spring-type retaining ring. 
   The external tubular housing  234  is removable from the light assembly, and is held in place by any convenient means such as setscrew  250 . The external tubular housing  234  is preferably metal, such as aluminum or steel, or alternatively made of high impact plastic. Removal of the external housing allows access to the bulb  232  and replacement of the bulb when it burns out. 
   Wire  260  leading to the light housing is coiled as shown within the quill housing, to allow movement of the light assembly with the quill  116 . Between the quill housing and the light housing, the wire is encased in flexible tubing, which allows it to be positioned, and to hold any desired position. The LED lamp works off of 120v, 220/240v, or 440/480v single phase and 3-phase that is convertible to 24v or less direct current without the use of batteries. A transformer accomplishes the voltage conversion. 
   Being affixed directly onto the quill  116  through a transition fitting  258 , the LED lamp continuously brightens the work area of the machine tools and surface of the part being machined by being properly directed. The light moves up and down with the machine tool. 
   The flexible tubing with the associated LED lamp gives the machine operator a large range of area for focusing the lamp beam onto the machine surface, workpiece, and tool. For the LED, the voltage must be converted to 12–24 volts. The higher voltage provides a brighter light. 
   The following voltages are commonly used with milling machines, and the present invention is adaptable to be used with any of them:
         120 V AC-3 phase   120 V AC-single phase   220/240 V AC-single phase   220/240 V AC-3 phase   440/480 V AC-3 phase       

   In operation, as a drill feed control lever  124  on the milling machine  100  is actuated, the quill  116  is vertically lowered to a workpiece on the table  112  and the indicator  16  positively and precisely measures the vertical travel, or depth, of the movement and digitally displays the unit of measure. Once the quill  116  is lowered to a predetermined depth limit, the quill stop bar  24  prevents further downward movement. 
   Referring to  FIGS. 6–8 , an alternative embodiment of the retrofit apparatus  10  is shown. The retrofit  10  comprises a mounting cover  12  having a left side  36 , a right side  38 , a face  40 , a top end  42  and a bottom end  44 . Again, the mounting cover  12  has a generally rectangular configuration and is preferably comprised of aluminum or steel. However, other, similar materials may be employed. Further, the face  40  has a generally rectangular aperture  46  located at the bottom end  44  of the mounting cover  12 . The retrofit  10  further comprises a main scale  14 , an indicator  16 , a hat clip clamp mount  50 , a cylindrical quill stop  24 , and a stop mount  26 . The aperture  46  in face  40  is of a corresponding size to the indicator  16 . 
   Similar to the first embodiment, the main scale  14  is a generally rectangular device formed so that the indicator  16  can be slidably mounted to the front surface thereof. The indicator  16  is slidably attached to the scale  14  and held in place by the hat clip mount  50 . The indicator  16  and scale  14  are attached to the mounting cover  12 . In addition, the upper end of the scale  14  is fixed to the front surface of the quill stop bar  24  by a face mount  52 . Preferably, the face mount  52  is attached to the quill stop bar  24  by a screw, however, it will be appreciated that other attaching devices may be used. Again, the quill stop bar  24  is held in place by the set screw  28 . 
   Subsequently, the entire retrofit assembly  10  is joined to the milling machine  100  by a plurality of screws which connect the connection points  132  located on the milling machine  100  and the notches  48  of the left and right sides,  36  and  38  respectively, of the mounting cover  12 . 
   Another alternative embodiment of the retrofit  10  is shown in  FIGS. 7 through 9 . In this alternative embodiment, the retrofit apparatus  10  comprises a mounting cover  12  having a generally rectangular configuration, a main scale  14 , an indicator  16 , a slide support  56 , a clamp mount  54 , a plurality of hat clips  20 , a plurality of screws  22 , a cylindrical quill stop bar  24 , a quill stop mount  26  which is adapted to receive the quill stop bar  24  and a cylindrical graduated rod  30 . 
   Again, the indicator  16  generally includes an indicator head having a digital readout  32  and a plurality of control buttons  34 . The indicator  16  further includes an attachment means whereby it can be secured to the main scale  14  by attachment screws. Further, the mounting cover  12  generally has a left side  36 , a right side  38 , a face  40 , a top end  42  and a bottom end  44 . The face  40  of the mounting cover  12  has a generally rectangular aperture  46  located toward the bottom end  44 . The aperture  46  in the face  40  is of a corresponding size to the indicator  16 . Located on the left and right sides,  36  and  38  respectively, are attachment notches  48  for attaching the retrofit apparatus  10  to the milling machine  100 . 
   The main scale  14  has a generally rectangular configuration and is formed so that the indicator  16  can be slidably mounted thereto. The slide support  56  has a substantially hat clip configuration and has a corresponding length to the scale  14 . However, the slide support  56  has a greater width than the scale  14 , thus allowing the scale  14  and indicator  16  to be fixed thereto by the plurality of hat clips  20  and screws  22 . Disposed between the slide support  56  and the indicator  16  is the clamp mount  54 . The indicator  16 , scale  14 , and slide support  56  are attached to the mounting cover  12  by the clamp mount  54  so that the indicator  16  is fixed within the aperture  46  of the mounting cover  12 . 
   After the scale  14  and indicator  16  are attached to the mounting cover  12 , they are attached to the quill stop bar  24 . The quill stop bar  24  is, in turn, matingly connected to the quill stop mount  26  at the upper end of its front surface. The graduated rod  30  is also matingly connected to the quill stop mount  26  at its bottom surface. The retrofit apparatus  10  is then fixed to the milling machine  100  in the manner previously described. 
   Referring to  FIGS. 12–14 , another embodiment of the present invention is shown. In this embodiment, a second generally elongated aperture  58  is present along side the aperture  46 . The second aperture  58  is of a shorter length and runs parallel to the aperture  46 . Displaced within the second aperture  58  is a hard stop block  60  having a T-bolt configuration. The hard stop block  60  has an additional lock lever  62  which, when engaged allows a user to set the block  60  along the second aperture  58  at a predetermined point. In operation, the user moves the hard stop block  60  to a desired location on the second aperture  58  and locks it in place by engaging the lock lever  62 . Once the quill  116  is extended, the rear plate  18  contacts the hard stop block  60  and resists further extension. This feature allows the user to mill multiple workpieces at a consistent depth. 
     FIGS. 22 and 23  show sliding stop plate  200  attached to the digital indicator, and fixed plate  202 . Finished cap nut bushing  206  is installed at the end of the quill. The digital displacement indicator  16  is mounted on a mounting plate  204  which transmits motion around the threaded rod to which the stop nut  150  is connected. While one end of the threaded rod is firmly attached to a fixed mount  202  attached to the cover, the motion of the digital displacement indicator can be stopped or adjusted with the stop nut  150 . Mounting plate  204  is of sufficient length to overlap both ends of the indicator  16  and provide protection thereto from damage. 
   The invented quick adjusting nut  150  includes a nut body  152 , a depressable plunger  154 , and a biasing mechanism, such as a compression spring  156 . 
   As best seen in  FIGS. 15 and 16 , nut body  152  includes an axial bore or passageway  158  adapted to receive a threaded rod or shaft  160 . Axial bore  158  is suitably centrally located through nut body  152 . In addition, a transverse bore or socket  164  extends radially inward from one exterior point across the diameter of nut body  152  communicating with axial bore  158  and terminating at an end  166  in the opposite half of body  152  beyond the axial bore. Socket  164  may have a tapered end  166 , as shown in  FIG. 15 , or it may have a flat end. 
   Nut body  152  may include a knurled end portion  168  for easy handling. The nut body  152  can also be provided with an upper graduated portion  170 , including any desired number of precision graduations. 
   Axial bore  158  is centrally disposed, extending through the nut body  152 . The diameter of axial bore  158  is selected to closely receive rod  160 , permitting sliding in an axial direction, but relatively little lateral motion. 
   Plunger  154  is adapted to be slidably received in transverse bore  164 , and has an outer end  172  accessible from the body exterior. Plunger  154  includes a transverse aperture  174  defined by two slightly offset bores  176  and  178  (see  FIG. 21 ). Unthreaded bore  176  is disposed nearest the end  172  of plunger  154 , and is of a larger diameter than bore  178 . It is suitably of slightly larger diameter than nut body axial bore  158  (e.g., 0.505 to 0.510 inch diameter). Smaller bore  178  is suitably offset from bore  176  by approximately 0.085 to 0.075 inch, and is of a diameter commensurate with that of threaded rod  160 , and is threaded in a manner suitable for threaded engagement or mating with the threads of rod  160 . 
   Plunger  154  is received in nut body transverse bore  164  so that aperture  174  is in general registry with nut body axial bore  158 . Nut body axial bore  158  and plunger aperture  174  are adapted to cooperatively receive threaded rod  160 . Biasing means such as spring  156  is placed in the terminal end  166  of nut body transverse bore  164  so that the compressive spring forces will operate in the axial direction of nut body transverse bore  164 , and, in the absence of external compressive force, will push threaded bore  178  into threaded engagement with rod  160 . 
   The quick adjusting nut  150  is easily placed in an operative condition on rod  160 . The nut is assembled, plunger  154  is depressed, and the nut  150  is mounted onto threaded rod  160  by sliding rod  160  through nut body axial bore  158  and plunger aperture  174 . 
   Coarse positioning of nut  150  is quickly and efficiently achieved by depressing plunger  154  to release the nut, and axially sliding nut  150  to the approximate desired location on rod  160 , as determined by visual coordination with machine mounted scale  21 . More particularly, depressing plunger  154  inwardly in a radial direction compresses spring  156 , and displaces plunger aperture  174  from the spring biased (engaged) position with respect to rod  160 . Rod  160  is thus disengaged from threaded bore  178  and is received in the larger diameter bore  176  of plunger aperture  174  to permit the axial sliding of nut  150  with respect to the threaded rod or shaft  160 . Plunger  154  is then released, whereby spring  156  biases the smaller threaded bore  178  of the plunger aperture  174  into threaded engagement with the threads of rod  160 . 
   Plunger aperture  174  is formed with offset bores  176  and  178  of differing diameters. By using a smaller threaded bore of a diameter corresponding to that of rod  160 , nearly a full 180 degrees of threaded engagement between nut  150  and rod  160  is provided during thread engagement. Further, the relatively close reception of rod  160  by nut axial bore  158 , and the extended length of the axial bore help to effectuate a secure threaded engagement. 
   Final securing of the stop nut  150  is by a set screw  182  which extends through the face  180  of the nut body  152 . A cooperating recess  184 , which is preferably conical is provided in the plunger. The set screw presses against the edge of the conical recess farthest from the spring in a cam-type action, effectively tightening the clamping effect of the threads of bore  178  of the plunger against the threads of the rod  160 . This has been found to be sufficiently tight to prevent movement of the nut under all normal operating conditions. 
   A slot  186  of lesser depth than the recess  184  is advantageously positioned in plunger  154  adjacent to and communicating with recess  184  to allow longitudinal movement of the plunger without complete removal of the set screw  182 . 
   Any biasing means can be substituted for spring  156 . A suitable biasing means is a leaf spring  190  as shown in  FIGS. 19 and 20 . Note that this requires a slight modification to the spring so that it will fit into the bore  152 . Advantageously, the leaf spring is welded to the end of the plunger. 
   Precision adjustment is achieved by rotating the nut  150  about rod  160  as desired, and is facilitated by graduation portion  170  of nut body  152 . 
   The nut is shown as round in  FIG. 16 , however, it can have a generally square or hexagonal configuration, if desired. 
   The set screw  182  can have a knurled head for hand tightening, or it can have a recessed head for an Allen wrench, or it can have a square or hexagonal head for engagement by a mating wrench. 
   The stop nut can be made of any desired material, including steel, stainless steel, brass, or aluminum. If steel, it can be black oxide or phosphate coated. If aluminum, it can be anodized, and can be made in different colors. If brass, it can be copper plated or chrome plated. 
   It should be appreciated that the present invention provides a particularly useful device. For example, when used in a machine shop wherein about 20 quick stop adjustments are required per day, a nut  150  in accordance with the present invention will save several man hours per month, as compared to conventional adjustment mechanisms. Further, a very tight and secure engagement between nut  150  and rod  160  is provided, which is not susceptible to undesired slippage due to vibration, nor is it susceptible to jamming. 
   A rotary cam selector switch  270 , available from BACO Controls, Inc., of Cazenovia, N.Y., is provided at or near the top of the retrofit assembly. This three-way switch provides Forward, Reverse, and Off settings on the same switch, which is small and compact. Most motors do not have a motor switch, but need a power switch to control the power to the motor switch. A pilot switch can be used where the motor has a motor switch. The 3-way switch  270  allows all of the current to move through it without requiring a motor switch. The advantage is that it is not necessary to modify the digital quill system to use different switches or different motors. For instance, in the invented system, a mill drill can use a 1 horsepower, a 1.5 HP, or a 2 HP motor without changing the switch. 
   While the present invention is described in connection with milling machines, it has advantageous application with other machines such as drill presses, and on any threaded drive where it is desired to stop motion precisely. 
   SUMMARY OF THE ACHIEVEMENT OF THE OBJECTS OF THE INVENTION 
   From the foregoing, it is readily apparent that I have invented a retrofit apparatus for economically measuring the vertical movement of a quill during operation, as well as a stop nut for milling machines which accurately and tightly holds against vertical movement of a quill during operation, which stop nut can be adapted and retrofitted to various machines having a threaded drive where it is desired to stop motion precisely. 
   It is to be understood that the foregoing description and specific embodiments are merely illustrative of the best mode of the invention and the principles thereof, and that various modifications and additions may be made to the apparatus by those skilled in the art, without departing from the spirit and scope of this invention, which is therefore understood to be limited only by the scope of the appended claims.