Abstract:
A press for securing a captive screw assembly within a hole in a panel cover. The press is supported from the panel cover as it is operated and includes a tool for extracting the captive screw assembly from the panel cover hole when the captive screw assembly is no longer functional. The extraction tool engages a bottom end of the captive screw and severs the flare on the ferrule of the captive screw assembly that anchors the assembly to the hole in the panel cover. A captive screw assembly is also described that has a knurled end that anchors the captive screw assembly to a hole in the panel cover.

Description:
BACKGROUND OF THE INVENTION 
     1. Field 
     This invention pertains generally to captive screw assemblies, and more particularly, to the installation and removal of captive screw assemblies applied to a panel cover. 
     2. Related Art 
     Captive screws are used to releasably attach panels over an opening or secure a door closed. Captive screws have the advantage that once the screw is disengaged from a threaded hole underlying the panel or door jamb to which the captive screw is attached, there are no loose parts that can get lost or fall into crevices in the equipment protected by the door or panel where the impact of the falling screw may cause damage to sensitive equipment. The captive screw is generally attached to a panel such that the captive screw is in alignment with a hole in the panel. The hole in the panel is aligned with a threaded hole in the structure underlying the panel when the panel is in the closed position. The screw is engaged to the threaded hole to secure the panel in the closed or attached position. The screw is disengaged from the threaded hole to allow the panel to be removed or the door opened. 
       FIG. 1  illustrates a cross section of a captive screw assembly  10 . The captive screw assembly  10  includes a captive screw  12 , a sleeve or ferrule  14 , and an optional spring  16 . As previously mentioned, the captive screw fastener  10  releasably secures a closure member in the closed position. As an example, the captive screw  10  can be used to secure the access panels of electrical equipment over the access openings in, for example, a PSA (Power Switch Assembly) in a nuclear power generation facility. The screw  12  has a screw head  18  and a shaft  20  having a threaded section  22 . An annular flange  24  is provided on the shaft  20  intermediate the screw head  18  and the threaded section  22  of the shaft  20 . The annular flange  24  or first flange may be spaced apart from the screw head  18  as shown in  FIG. 1  or may be secured adjacent the screw head. The ferrule  14  has a hollow bore  26 , a panel engaging end  28 , and a screw retaining end  30 . A portion of the screw shaft  20 , including the annular flange  24  is housed within the bore  26  of the ferrule  14  with the annular flange  24  being captured between the ends  28  and  30  of the ferrule  14  by the ferrule internal shoulder  46  in the panel engaging end and the screw retaining end flange  40 , respectively. The screw  12  is axially movable relative to the ferrule  14  between an extended position in which the annular flange  24  approaches the panel engaging end  28 , and a retracted position in which the annular flange  24  approaches the screw retaining end  30 . In addition, the screw  12  can rotate freely relative to the ferrule  14  about the screw&#39;s own central longitudinal axis. In the extended position, the threaded portion  22  of the screw shaft  20  projects from the panel engaging end  28  of the ferrule  14  to its maximum amount. The amount of projection of the threaded portion  22  of the screw shaft  20  from the panel engaging end  28  of the ferrule varies as the screw is moved relative to the ferrule. In the retracted position, the amount of projection of the threaded portion  22  of the screw shaft from the panel engaging end  28  of the ferrule is at its minimum. In some embodiments, the threaded portion  22  of the screw shaft may be completely retracted into the bore  26  of the ferrule  14  when the screw  12  is moved to the fully retracted position. 
     The screw head  18  is typically located outside the ferrule  14  where it can be accessed by a user&#39;s fingers for tightening or loosening the screw  12 . The screw  12  may be provided with knurling or serrations on the peripheral surface  32  of the screw head  18  to give the user&#39;s fingers a better grip. The panel engaging end  28  of the ferrule  14  is designed to engage a hole  34  in the panel  36 ; the panel  36  being the panel that is to be secured by the captive screw assembly  10 , in order to attach the ferrule  14  to the panel  36 . The screw retaining end  30  has a hole  38  that allows the shaft  20  of the screw  12  to extend through the hole  38  and into the bore  26 , however, the diameter of the hole  38  in the screw retaining end of the ferrule is less than the diameter of the annular flange  24  such that the annular flange  24  remains captured within the bore  26  of the ferrule  14 . The screw retaining end  30  of the ferrule may be formed by a second annular flange  40  which projects from the peripheral wall  42  of the ferrule  14  inward toward the central longitudinal axis of the ferrule. The panel engaging end  28  of the ferrule  14  also has a hole  44  that provides clearance for the shaft  20  of the screw but is too small in diameter to allow the annular flange  24  of the screw to clear the opening  44  in the panel engaging end  28  of the ferrule. Peripheral to the hole  44  in the panel engaging end of the ferrule is a shoulder  46  which acts as a seat for one end of the optional spring  16  that may be provided intermediate the flange  24  of the screw and the panel engaging end  28  of the ferrule. This optional spring  16  acts to bias the screw  12  toward the retracted position once the screw is disengaged from the threaded hole (not shown) in the structure underlying the panel  36 . The captive screw assembly  10  is attached to a panel  36  such that the screw  12  is in alignment with the hole  34  in the panel  36 . The hole  34  in the panel  36  aligns with a threaded hole (not shown) in the structure underlying the panel  36  when the panel  36  is in the closed position. The screw  12  is engaged to the threaded hole to secure the panel  36  in the closed or attached position. The screw  12  is disengaged from the threaded hole to allow the panel  36  to be removed. 
     In the prior art embodiment illustrated in  FIG. 1 , the panel engaging end  28  is formed by a portion of the ferrule which has reduced internal and external diameters. This reduced diameter portion is then flared outward giving the panel engaging end  28  a U-shaped cross section with the concave side of the “U” shape facing outward away from the central longitudinal axis of the ferrule. The reduced diameter portion of the panel engaging end  28  also forms an exterior shoulder  48  which abuts the surface of the panel  36  once the captive screw assembly  10  is mounted to the panel  36 . The ferrule  14  can be pressed in or crimped to the hole  34  such that the surface  50 , which surrounds the bottom rim  52  of the panel engaging end  28 , is pressed against the sidewall of the hole  34  to thereby press fit the ferrule  14  to the panel  36 . The panel engaging end  28  may be made in a variety of different configurations such as the press-in type depicted in  FIG. 1 , the snap-in type, the threaded type, the swaged type, etc. 
     It is sometimes difficult to assure that the captive screw assemblies are securely attached to the panel cover to avoid the captive screw assemblies from being dislodged and possibly dropping into sensitive instrumentation within the cabinets, potentially damaging the instrumentation. 
     According, means are desired that can adequately secure the captive screw assemblies to assure they will not be readily dislodged. Furthermore, such a means is desired that will produce a consistent result. 
     Additionally, a means is desired that will disengage such captive screw assemblies that have been securely attached if they become damaged or otherwise are unable to fulfill their intended function. 
     Further, a new captive screw assembly is desired that will enhance the attachment coupling between the screw assembly and the panel cover. 
     SUMMARY OF THE INVENTION 
     These and other objects are achieved by the embodiments described herein which provide a captive screw press and related equipment for operating on a captive screw assembly in relation to an opening in a panel cover. The captive screw press includes a base having an upper surface with a front portion and a rear portion. The captive screw press also includes a platform having an underside with a front portion and a rear portion. The rear portion of the platform is attached to the base and affixed to the rear portion of the base with one or both of either the rear portion of the upper surface of the base and/or the rear portion of the underside of the platform extending towards the other so that the front portion of the base is spaced from the front portion of the platform. A clamp is attached to either the front portion of the upper surface of the base or the front portion of the underside of the platform. The clamp is movable to extend toward the other of the front portion of the base or the front portion or the underside of the platform so as to clamp the panel cover therebetween. A hole in the top of the platform extends along an axis through the platform into the space between the underside of the front portion of the platform and the upper surface of the front portion of the base. A force arm is coaxially movable within the hole to place a force on the captive screw assembly when placed in the hole, with at least one of either the force arm or the captive screw assembly being rotatable when it moves in the hole. The captive screw press also has a thrust bearing attached to an underside of the force arm between the captive screw assembly and the force arm when the force arm places the force on the captive screw assembly to drive the captive screw assembly in the direction of the panel. 
     In one embodiment, the sidewalls of the hole includes bearings to hold the captive screw assembly within the hole prior to the force arm applying a downward pressure on the captive screw assembly. Preferably, the bearings are spring biased towards the axis of the hole. In still another embodiment, the clamp includes an insert in either the upper surface of the base or the underside of the platform, which extends into or withdraws from the space between the base and platform in response to the operation of a set screw. 
     Preferably, the platform and the base are constructed from metal including a co-polymer lining on at least a portion of the upper surface of the base and at least a portion of the underside of the platform. In one of the embodiments, the force arm is preferably a threaded screw. Desirably, a raised columnar structure extends upward from the upper surface of the platform and has a central opening that extends axially through the columnar structure and mates coaxially with the hole, with the central opening in the columnar structure being at least partially threaded with a thread pitch that matches the threaded screw. 
     In still another embodiment, the captive screw press includes an opening in the base that extends from an underside of the base through the upper surface of the base coaxial with the hole in the platform. Preferably, the base is separable from the platform. 
     In operation, a captive screw assembly is disposed within the hole in the platform below the force arm and has a ferrule with a central bore capturing a captive screw. The ferrule has an upper section opposed to the thrust bearing on the force arm and a lower section with a reduced diameter sized to be pressed within the opening in the panel cover. Preferably, the lower section has a knurl over at least a portion of its peripheral surface, that causes the knurl to bite into a wall of the opening in the panel cover and turn the ferrule during insertion of the captive screw assembly into the opening in the panel cover. Desirably, the lower section of the ferrule extends in the axial direction a distance sufficient to substantially fully insert the reduced diameter portion of the lower section of the ferrule with the bottom of the ferrule recessed in the underside of the panel. Furthermore, a flaring tool is also provided for flaring the portion of the lower section of the ferrule so that the knurled end is locked against the sidewall of the hole in the panel cover. Desirably, the captive screw press also includes an extraction tool for removing the flared lower edge on the captive screw assembly from the underside of the panel. The extraction tool includes an elongated shaft having a female threaded recessed end at one end that matches the thread on the captive screw and an impact face at the other end. The one end having the female threaded recess, has a beveled outer surface that flares outward, away from the female threaded recess towards the other end. The female threaded recess has a cutting edge substantially surrounding its distal end for cutting through the flared lower portion of the ferrule. 
     The embodiments described herein also include a method of fastening a captive screw assembly to a panel. The method includes the step of placing a captive screw press over a surface of the panel and centering an opening in the captive screw press for holding the captive screw, over a hole in the panel into which the captive screw assembly is to be pressed, using a centering tool that is inserted through the bottom of the captive screw press into the hole in the panel. The steps of the method further include clamping the captive screw press to the panel and tightening a force arm through the opening to press the captive screw assembly into the hole in the panel. The method then includes the step of loosening the clamp that clamps the captive screw press to the panel to remove the captive screw press from the panel. 
     In a preferred embodiment, the captive screw press has an upper and lower portion and the step of loosening the clamp to remove the captive screw press from the panel includes the step of separating the upper and lower portion of the captive screw press. Furthermore, the method may include the step of rotating the force arm as it is tightened. 
     The embodiments described herein also contemplate a captive screw assembly to be pressed into an opening in the panel cover for securing the panel cover to the panel housing. The captive screw assembly includes a ferrule with a central bore, with the ferrule having an upper section and a lower section. The upper section has a first diameter and the lower section has a second diameter which is smaller than the first diameter and sized to be pressed within the opening the panel cover. The lower section has a knurl over at least a portion of its peripheral surface that causes the knurl to bite into a wall of the opening in the panel cover as the lower section is pressed into the opening and causes the ferrule to turn during insertion of the captive screw assembly into the opening in the panel cover. The captive screw assembly also includes a captive screw which is captured substantially within the central bore of the ferrule. 
     The embodiments described herein further contemplate an extraction tool for removing the flare on a captive screw assembly from the underside of a panel. The extraction tool includes an elongated shaft having a first and second end. A female threaded recess is provided at one end with the pitch on the thread on the recess matching the pitch on the thread on the captive screw. The first end with the threaded recess also has a beveled outer surface that flares outwardly, away from the female threaded recess towards the second end. An impact face is configured at the second end. Preferably, the beveled outer surface in the first end terminates in a cutting edge and the diameter of the portion of the elongated shaft adjacent the first end between the beveled outer surface and the second end has a diameter smaller than the second end. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A further understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
         FIG. 1  is a cross sectional view of a prior art captive screw assembly positioned above a hole in a panel; 
         FIG. 2  is a schematic view of the captive screw press of this embodiment; 
         FIG. 3  is a schematic view of the captive screw press of this invention with a number of the internal features shown in phantom; 
         FIG. 4  is a schematic view of the captive screw press of this embodiment with a number of the internal features shown in phantom; 
         FIG. 5  is a perspective view of the drive screw of the captive screw press shown in  FIG. 2 ; 
         FIG. 6  is a side view of the thrust bearing retaining pin that is inserted at the end of the drive screw shown in  FIG. 5  and employed for securing the thrust bearing at the end of the drive screw; 
         FIG. 7  is a perspective view of the captive screw of this embodiment; 
         FIG. 8  is a schematic view of the ferrule of the captive screw shown in  FIG. 7  with the internal bore illustrated in phantom; 
         FIG. 9  is a cross-sectional view of the extraction tool of this embodiment shown partially in cross section; and 
         FIG. 10  is a cross sectional view of a captive screw assembly in accordance with this invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The captive screw press of this embodiment is employed to fasten a captive screw assembly to a panel cover in a convenient and secure manner. A schematic view, partially in section, of the captive screw press  54  is shown in  FIGS. 2 ,  3  and  4 , and includes three main parts. The lower half or base  56  is the first main part and is preferably constructed from a metal such as 303 stainless steel. The base  56  has a front section  58  and a rear section  60  which interface at a step  62 . The upper surface  64  of the front section  58  of the base  56  is preferably lined with a thermoplastic polymer  66 , such as Delrin®, which in this embodiment is fastened to the base with the screws  68 . The upper working half or platform  70  of the captive screw press  54  is the second main part and is preferably made of a metal such as heat treated 17-4 stainless steel. The platform  70  has a front section  72  and a rear section  74  with a portion of the rear section  74  extending below the front section  72  and mating with an upper surface of the rear section  60  of the base  56  at the interface  78  to form a space  80  between the undersurface of the front section  72  of the platform  70  and the upper surface of the front section  58  of the base  56 . Alternatively, the rear section  60  of the base  56  can be raised or both the sections  56  and  74  can be raised to form the space  80 . The lower surface  82  of the front section  72  of the platform  70  similarly has a thermoplastic polymer liner that is secured in place by the screws  86 . The rear sections  60  and  74  are aligned with one another by the dowels  92  and fastened together by the bolts  94  which can be seen in  FIGS. 3 and 4 . The bolts  94  are countersunk in the recesses  96 . As can be seen in  FIGS. 2 ,  3  and  4 , the platform  70  also includes a columnar structure  88  that rises above an upper surface of the platform  70  and has a threaded central bore  90  which extends into and is coaxial with an opening  98  through the platform, which extends from the threaded central bore  90  to the space  80  between the front sections  58  and  72 , respectively of the base  56  and platform  70 . The opening  98  is sized to accommodate a captive screw assembly  10 , such as previously described with regard to  FIG. 1  or as shown in  FIGS. 7 ,  8  and  10 . A slot  91  in the front of the platform  70  communicates with the central opening  98  and is sized to facilitate placement of the captive screw assembly  10  into the opening  98 . 
     The space  80  between the front sections  72  and  58 , respectively of the platform  70  and base  56  is sized to accommodate the width of the panel cover which is to be clamped between the front sections  58  and  72 . The liners  66  and  84  are provided to prevent damage to the panel cover as the cover is clamped therebetween. Discs  100  are slidably mounted in recesses  102  in the upper surface  64  of the front section  58  of the base  60  and are raised or lowered by set screws  104  to apply the desired clamping force. Alternatively, the discs can extend from the undersurface of the front section  72  of the platform  70 . Additionally, spring biased ball bearings  106  extend slightly from the walls of the opening  98  and are retained in position by the set screws  108 . The ball bearings hold the captive screw assembly  10  in position within the opening  98  until it is forced through the opening  98  into a hole  34  that is provided in the panel cover. The columnar structure  88  can be supported in a recess machined in the top of the platform  70  over the opening  98  and secured in place with the set screw  128  shown in  FIG. 4 . Such a configuration would enable the columnar structure to be removed for easy insertion of the captive screw assembly into the opening  98  if a slot  91  is not provided for that purpose. Alternately, the columnar structure  88  can be formed as an integral part of the remainder of the platform  70  or the columnar structure can be welded to the top of the platform  70 . In the latter two cases, the captive screw assembly can be loaded into the opening  98  by separating the platform from the base if a slot  91  is not provided. The slot  91  is the most convenient and efficient alternative. 
     The third main component of the captive screw press is the drive bolt  110  shown in  FIGS. 2 and 5 . In this embodiment, the drive bolt  110  is a ½-20, 3 inches (7.62 cm) long with a ¾ inch (1.91 cm) hex head  112 .  FIG. 5  shows the drive bolt  110  with an optional integral flange or washer  114 . On the lower end of the drive bolt  110  shown in  FIG. 2 , there is a thrust bearing  116  that is free to turn independent of the rotation of the drive bolt  110  or the head of the captive screw, to prevent damage to the head of the captive screw. The thrust bearing  116  is rotatably secured to the bottom of the drive bolt  110  by shaft pin  118  (also known as a “top hat”), which passes through the axis of rotation of the thrust bearing and into a recess  120  in the lower end of the drive bolt  110  and is secured in place by a 4-40 set screw  122 . The set screw  122  extends into an annular recess  119  in the shaft pin  118  and loosely retains the shaft pin so it can rotate with the thrust bearing  116 . The drive bolt  110  has a thread  124  which extends at least partially along the upper shaft  126  of the drive bolt  110  and matches the pitch on the thread in the internal bore  90  of the columnar structure  88 . When pressure is applied to the captive screw assembly by the drive bolt  110 , the thrust bearing  116  will rotate with the screw head of the captive screw and drive it downward into the panel cover as the drive bolt  110  is rotated in a direction that will move it towards the panel cover clamped in the space  80  between the lower surface  82  of the front portion  72  of the platform  70  and the upper surface  64  of the front portion  58  of the base  56 . 
     The press  54  can be used with either stainless steel or aluminum captive screws, or even captive screws made out of a variety of other materials. The press  54  can be applied to the edge of the panel and located on a center line of the hole in the panel in which it is to be inserted, employing a locator such as the extraction tool  130  shown in  FIG. 9 . The reduced diameter end  132  of the extraction tool  130  is inserted through a hole  134  in the base  56  and through the hole in the panel to align the hole in the panel with the center line of the opening  98  in the platform front section  72 . Once located on the center line the two set screws  104 , shown in  FIG. 2 , on the bottom half of the press  54  can be tightened which drives the discs  100  against the Delrin® liner  66  and clamps the press securely to the front panel. Once the press is secure, the locator  130  can be removed and the captive screw assembly can be inserted into the opening  98  of the press  54  and pressure can be applied by the drive bolt  110 , driving the captive screw assembly into the panel and snugging it into place. If the ferrule is made of a relatively soft metal, e.g., aluminum, a flaring tool such as the one described in U.S. Pat. No. 6,761,521, can be applied through the hole  134  in the base to flare the bottom of the ferrule outwardly against the underside of the panel cover, which will secure the ferrule of the captive screw assembly to the panel cover. The flare is particularly effective if the underside of the hole  34  in the panel  36  has a chamfer. 
     This embodiment also contemplates an improved captive screw assembly  10  shown in  FIGS. 7 and 10 , with the ferrule shown in more detail in  FIG. 8 . Like reference characters to that employed in  FIG. 1  are used in  FIGS. 7 ,  8  and  10  to identify corresponding components. Withdrawal of the captive screw from the ferrule is prevented by a flange or washer  114  on the screw shaft  20  abutting the radially inward protecting flange  40  on the wall of the ferrule bore  26  and the screw head  18  interface with the top of the ferrule  14 . A major improvement is the use of angled knurls on the peripheral surface of the reduced outside diameter lower portion  52  of the ferrule  14 . The angled knurls cause the captive screw assembly to rotate when pressed by the drive screw  110  into the opening  34  in the panel cover  36 . The captive screw assembly rotates in the direction of the knurl with a screw affect, cutting into the wall of the panel hole  34 , which will secure itself in the hole. The captive screw assembly is preferably made of stainless steel, and desirably heat treated 17-4 stainless steel and employs a Delrin® washer  114  which when pressed in place holds a ¼-20 spring and screw in place within the screw retaining end  30  of the ferrule  14 . As can be appreciated from  FIG. 10 , the Delrin® washer  114  is assembled by being pressed in from the bottom side of the tapered bore  26 . The washer inside diameter is approximately 0.005 inch (0.013 cm) smaller than the major diameter of the thread  22 , which makes it easy to screw through the washer. 
     The press  54  may be used with different sizes of captive screw assemblies  10  by using split sleeves  148  of different widths, that fit over the ferrule  14  as shown in phantom in  FIGS. 7 and 10 . The split sleeves  148  may also be made out of the Delrin® polymer and is designed to substantially fill any gap between the outside diameter of the ferrule  14  and the inside diameter of the opening  98 . 
     The embodiments described herein also contemplate an extraction tool for removing the captive screw assembly from the panel cover. The extraction tool  130  is illustrated in  FIG. 9  and is preferably made from heat treated 17-4 stainless steel. The extraction tool  130  has an elongated shaft  146  with a knurled end  136  and a reduced diameter section  132  at the other distal end. The reduced diameter section  132  terminates at its distal end with a beveled section  140  that at its tip has a cutting edge  142  that surrounds a threaded recess  144 . The pitch of the threads in the recess  144  match the pitch of the threads on the captive screw assembly. The extraction tool  130  can be screwed onto the captive screw from the rear side of the panel. The cutting edge  142  centers the tool in the flared part of the captive screw assembly. The beveled section  140  limits the extent of the cut. Once the tool is centered, the tool is rotated in a clockwise direction as tight as the operator can manage by hand. At that point, a hammer can be applied to the backside of the tool at the end of the knurled end  136 . One or two hits with the hammer are usually all that is required to sever the flared part of the captive screw  12 . Once that has been done, the tool can be unscrewed from the captive screw and the captive screw assembly can be pulled from the panel hole from the front side of the panel. 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. For example, an alternate force arm can be substituted for the drive bolt. Furthermore, the dimensions and materials described herein are meant to be illustrative only, and alternatives can readily be accommodated. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.