Patent Publication Number: US-11397063-B2

Title: Jig for manufacturing of firearm lower receiver

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/206,878, filed Nov. 30, 2018, now U.S. Pat. No. 10,718,578, entitled IMPROVED JIG FOR MANUFACTURING OF FIREARM LOWER RECEIVER, which application is a continuation of U.S. application Ser. No. 15/979,322, filed May 14, 2018, now U.S. Pat. No. 10,145,633, entitled IMPROVED JIG FOR MANUFACTURING OF FIREARM LOWER RECEIVER, which application is a continuation of U.S. application Ser. No. 15/726,351, filed Oct. 5, 2017, now U.S. Pat. No. 9,982,958, entitled IMPROVED JIG FOR MANUFACTURING OF FIREARM LOWER RECEIVER, which application claims the benefit of U.S. Provisional Application Ser. No. 62/404,710, filed Oct. 5, 2016, entitled IMPROVED JIG FOR MANUFACTURING OF FIREARM LOWER RECEIVER, the entire disclosures of each of which applications are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to systems and methods for manufacturing an 80% (partially unfinished) firearm receiver, with a high rate of success with improved quality, by an unskilled user. 
     BACKGROUND OF THE INVENTION 
     A market exists for incompletely/partially manufactured firearm lower receivers. A firearm lower receiver is unregulated until a minimum level of manufacturing is completed. This level is typically known as “80%”. Firearm lower receivers completed to this level are typically referred to as “80%” lower receivers. These firearms must then be completed by the end user to be operable. In a typical configuration the lower receiver is cast and/or forged and is partially machined, with certain aspects of the inner slot (in which the trigger mechanism resides) remaining uncut. The finishing task cuts this remaining slot with appropriate dimensions and accuracy. 
     The completion of these lower receivers can be time consuming and quality results may be difficult to achieve with prior art. In accordance with the prior art, the technique for finishing the receiver can place a rotary power tool in a position that is effectively too far away from the lower receiver. As such this prior art technique can produce poor results and broken tooling. Additionally, the prior art technique can involve placement of a rotating tool in direct contact with guiding areas of a jig, which can result in premature wear. 
     It would be desirable to provide a jig assembly that effectively reduces the unsupported distance between the rotary power tool and the 80% lower receiver and that avoids direct contact between the rotating tool and its guiding features. 
     SUMMARY OF THE INVENTION 
     This invention overcomes the disadvantages of the prior art by providing a device that reduces the distance between the lower receiver and the rotary power tool and by using additional features to guide the rotary tool instead of placing it in direct contact with any of the plurality of guiding features. An improved jig for manufacturing a firearm lower receiver is comprised of a power tool mount; an adapter; a guide plate with plate screws; a rear support with mounting screws; a front support; and at least one carriage with at least one locating pin. A guide plate is disposed around and below the top surface of a lower receiver and is mounted to the carriage(s) in conjunction with a rotary power tool adapter. The jig is a universal fitment. The jig includes a bearing to support a rotary tool and is constructed and arranged to provide for use of at least one guiding feature to facilitate in the guidance of the rotary tool without placing the rotary tool in direct contact with any of a plurality of guidance features for firearm lower receiver manufacturing. A removable locating pin is situated in a location along the front and rear takedown pin holes of a firearm receiver that is not threaded and is provided with at least one of a pull, a string or other handle for firearm lower receiver manufacturing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention description below refers to the accompanying drawings, of which: 
         FIG. 1  is an exploded right side view of an improved jig, according to an illustrative embodiment; 
         FIG. 2  is a right side view of the improved jig, according to the illustrative embodiment; 
         FIG. 3  is an exploded rear view of the improved jig, according to the illustrative embodiment; 
         FIG. 4  is a rear view of the improved jig, according to the illustrative embodiment; 
         FIG. 5  is an exploded left side view of the improved jig, according to the illustrative embodiment; 
         FIG. 6  is a left side view of the improved jig, according to the illustrative embodiment; 
         FIG. 7  is an exploded front view of the improved jig, according to the illustrative embodiment; 
         FIG. 8  is a front view of the improved jig, according to the illustrative embodiment; 
         FIG. 9  is a exploded perspective view of the improved jig, according to the illustrative embodiment; 
         FIG. 10  is a perspective view of the improved jig, according to the illustrative embodiment; 
         FIG. 11  is a top view of the improved jig, according to the illustrative embodiment; 
         FIG. 12  is a top view of the improved jig, according to the illustrative embodiment; 
         FIG. 13  depicts a method of jig assembly according to one or more aspects of the disclosure; 
         FIG. 14  depicts a method of drilling with a jig assembly according to one or more aspects of the disclosure; 
         FIG. 15  depicts a method of milling with a jig assembly according to one or more aspects of the disclosure; 
         FIG. 16  depicts a method of milling with a jig assembly according to one or more aspects of the disclosure; 
         FIG. 17  depicts a method of milling with a jig assembly according to one or more aspects of the disclosure; 
         FIG. 18  depicts a method of drilling with a jig assembly according to one or more aspects of the disclosure; 
         FIG. 19  depicts a method of lower receiver removal using a jig assembly according to one or more aspects of the disclosure; 
         FIG. 20  depicts various components of a jig assembly with reference to  FIGS. 13-19 and 21-27 ; 
         FIGS. 21A-P  depict various stages of the method of  FIG. 13 ; 
         FIGS. 22A-I  depict various stages of the method of  FIG. 14 ; 
         FIGS. 23A-K  depict various stages of the method of  FIG. 15 ; 
         FIGS. 24A-K  depict various stages of the method of  FIG. 16 ; 
         FIGS. 25A-E  depict various stages of the method of  FIG. 17 ; 
         FIGS. 26A-G  depict various stages of the method of  FIG. 18 ; and 
         FIGS. 27A-E  depict various stages of the method of  FIG. 19 . 
     
    
    
     DETAILED DESCRIPTION 
     The primary function of a jig is to provide repeatability, accuracy, and interchangeability in the manufacturing of products. In  FIG. 1 , an improved jig  100  is assembled by placing left carriage  302  (see  FIG. 3 , not shown in  FIG. 1 ) on the left side of a lower receiver  116  and by placing right carriage  114 , on the right side of the lower receiver  116 . The lower receiver in this example is a form of popular AR-style receiver (for example the semi-automatic version of the AR-15, M-16, M-4 carbine, and variants thereof). The lower receiver is the portion of the firearm that includes a shoulder stock, pistol grip, trigger mechanism and magazine well. The upper receiver includes the barrel, chamber and bolt assembly. The lower receiver is attached to the upper receiver by two takedown pins. The firearm is available in fully automatic and semi-automatic versions. Note that the jig is adapted to finish the receiver with holes and cuts appropriate to the semi-automatic version. However, the jig can be adapted for the use by licensed manufacturers to finish other versions (e.g. fully automatic) of the firearm. The jig  100  is an assembly that is comprised of a rotary power tool mount  103 , an adapter  122 , a guide plate  108  with plate screws  106 ,  120 , a threaded rear support  110  with mounting screws  112 , a front support  118 , and at least one carriage  114  with at least one locating pin  306 . As described below, the plate screws  106  are machine screws with an appropriate diameter, thread size and length, and the screw  120  can also be a machine screw (for example, a #8-32 flat head machine screw), sheet metal screw, or another form of self-tapping screw. The receiving hole of the front support  118  is drilled and/or tapped to accommodate the screw  120 . The illustrative jig defines a universal fitment. A removable locating pin  306  (See  FIG. 3 ) is readily inserted through all three parts  302 ,  116  and  114  to hold them in alignment relative to each other. This renders assembly highly straightforward for use by even an inexperienced user. In an embodiment, the jig assembly can be provided as a kit with appropriate instructions (printed, on electronic media and/or available via the Internet). See for example, the instructions in attached Appendix A, which describe setup and use of the jig assembly. The kit can include a rotary power tool having an appropriate size, shape, torque and power supply. 
     As described herein, the lower receiver  116  includes a buffer mount  117  for receiving a buffer assembly within the shoulder stock at one end, and the front surface of the magazine well  119  at the other. As defined herein, the buffer mount  117  is at the “rear” end of the lower receiver, while the magazine well  119  is at the “front” end of the lower receiver. As presented in  FIG. 1 , the rear end of the lower receiver  116  is on the left side and the front end of the lower receiver  116  is on the right side and the visible face of the lower receiver is the “right” side. The right carriage  114  is resting on the right side of the lower receiver  116 . Thus, the relative orientation of the jig assembly  100  (i.e. left, right, front, rear, top and bottom) is described with respect to the corresponding, confronting sides of the lower receiver  116 . 
     Note that the carriage plate  114  is provided with three drill guide holes,  132 ,  134 ,  136 , along its side for the location of and drilling of appropriate diameter pin holes into the lower receiver  116 . These guide holes are used to guide and align a drill bit to bore desired holes into the lower receiver side. By way of non-limiting example drill guide hole  132  is a guide hole for a hammer pivot/pin hole, for the subsequent mounting of an assembly that retains the hammer mechanism within the lower receiver. Drill guide hole  134  is a guide hole for a trigger pivot/pin hole, for the later mounting of a trigger pivot/pin to retain the trigger mechanism. Drill guide hole  136  is a guide hole for a selector/safety pivot hole, for the subsequent mounting of a selector/safety lever. These carriage guide holes provide for the accurate and precise placement of the pin holes and are constructed so that an unskilled user can properly place the pivot/pin holes for completion of the assembly of a functioning lower receiver. Holes can be provided on each of opposing carriage plates to drill each side of the receiver in an embodiment. In alternate embodiments holes are provided on one side and the drill passes through both sides of the receiver. The thickness of the carriage plate(s) and close tolerance of the hole to the drill shaft is sufficient to ensure minimal skew or wobble as the drill passes into the receiver side. 
     The rotary power tool mount  103  is adapted to receive an appropriately sized and shaped rotary power tool  102 , as described further below. The rotary power tool retains an appropriate rotary tool  104  in accordance with various embodiments. The term “rotary tool” shall be taken broadly herein to mean any one of a variety of rotating cutting elements that can be mounted removably (or permanently) within a chuck or arbor of the rotary power tool  102 . For example a two-flute or four-flute end mill of appropriate diameter (for example, a ¼ inch diameter, or another appropriate diameter between (e.g.) ⅛ inch and ½ inch) can be mounted within the rotary power tool. The mill can include a cutting end and a shaft that is free of cutting surfaces. The shaft is adapted to confront the jig so as to avoid cutting its sides while the cutting end is adapted to reside within the receiver so as to cut the appropriate slot(s) in conjunction with the jig&#39;s outline(s). The rotary tool  104  can be constructed from a variety of high-strength materials, such as high-speed steel, tungsten carbide, etc. 
     As shown, the rear support  110  is threaded into lower receiver  116  via the receiver&#39;s rear buffer mount (a large round hole at the rear of the receiver in which a buffer assembly normally resides when assembled into a firearm). Front support  118  is placed between two mounting ears on the lower receiver  116  before an easily removable locating pin  704  inserted through the mounting ears of the lower receiver  116  and through the hole in the front support  118 . Illustratively, the front support  118  resides where the front pivot/takedown pin between the upper and lower receiver on a complete firearm normally resides. The pivot hole in this arrangement has been drilled by the supplier of the 80% receiver, and is, thus available for use in mounting the front support via pin  306 . As with other receiver holes and structures relied upon to engage the jig assembly, they are reliably located by the manufacturer using sophisticated tooling so that the jig accurately and repeatable mounted to the lower receiver  116 , and the corresponding cutting performed by the user is equally reliable and accurate. 
     After mounting the front support  118 , a guide plate  108  is then placed atop the assembly by aligning the holes in the guide plate  108  with the threaded holes in the front support  118 , the threaded holes in the rear support  110 , and the threaded holes in both the left and right carriages  302  and  114  respectively. The guide plate  108  has a thickness TC 1  of between ⅜ and up to ½ inch and a length LC 1  of approximately 8 inches (±0.5 inches). The adapter plate  122  has a thickness TC 2  of approximately ½ inch and a length LC 2  of approximately 4 inches (±0.5 inches). In other embodiments, these thicknesses and widths can vary greater or lesser, depending on the materials used. Once aligned, carriage-to-guide plate screws  106  are inserted through the guide plate  108  and tightened to connect the carriages  114  and  302  to the guide plate  108 . The rear support-to-guide plate screws are inserted through the holes in the guide plate  108  and tightened into the rear support  110 . The front support-to-guide plate screws  120  are inserted through the guide plate  108  and tightened into the front support  118 . These screws  120  can be sheet-metal screws or flat head screws (for example, a #8-32 flat head screw) and the hole(s) in the front support  118  can be sized to receive such screws. The carriage screw  304  is threaded to a corresponding female thread in the left carriage  302  and continued through a threaded hole in the right carriage  114 . Illustratively, both the left carriage  302  and right carriages  114  are threaded so if the assembly is placed into the jaws of an external vice or other clamp, it will tend to resist deformation that could damage the lower receiver  116  sandwiched therebetween. The screw  304  can have a recessed drive head (e.g. hex, star, etc.) so that it avoids interference with a clamping jaw (if any). The above thus defines the full set of components of the jig assembly, which are connected either directly or indirectly to the lower receiver  116 . 
     The illustrative jig assembly is depicted as retaining a rotary power tool  102  in the power tool mount  103 , but it is contemplated that the power tool can be a non-rotary tool. The jig provides for the use of at least one of the various guiding features (for example, left carriage  302 ) to be utilized to aid in the guidance of a power tool  102  without placing the tool in direct contact with any guiding feature. 
     Note that a wide variety of rotary power tools can be employed in association with an embodiment of the jig assembly—for example a small router, drill, hand piece of a flexible-shaft unit or Dremel®-style tool. The rotary tool can be cordless or powered by (e.g.) wall current via a power cable. 
       FIG. 2  depicts the jig  100  holding the rotary power tool  102  in engagement with the lower receiver  116  so that finishing work can be performed on the lower receiver. The receiver  116  is situated between the carriages  114  and  302  so that it remains in place during the finishing operation. There is a narrow gap between the carriages and the walls of the lower receiver  116 . The gap prevents contact between the surfaces of the carriages with the surface of the lower receiver and thereby prevents possible scratching of the surface coating of the lower receiver. In an alternate embodiment, the carriages can have an external flexible coating (for example, a polymer) and make contact with the surface of the lower receiver or a removable foam pad can be provided during assembly to avoid inadvertent contact between the carriage plate and the receiver during assembly of the jig. The various plates of the jig assembly can be constructed from a variety of materials, or combination of materials—for example aluminum alloy, steel, polymer (e.g. Delrin® (from DuPont), polycarbonate, acrylic, etc.). The thickness of each plate  108 ,  122  is also highly variable, and depends in part upon the choice of material(s). By way of non-limiting example, the thickness of the jig assembly plate(s) can be between ⅛ and ½ inch, or greater, for sufficient strength and rigidity. For example, the carriage plates  114  and  302  should define a sufficient thickness to receive the screws  106  within threaded holes formed in the top edge of each plate. Likewise, the guide plate  108  should be sufficiently thick to allow the rotary tool  104  to resist wobble. The various plates can be constructed from sheet stock and milled to shape using, e.g. CNC manufacturing techniques. Other methods of constructing the plates can be employed in alternate embodiments—for example stamping or casting with finish milling, 3D printing, molding, etc. 
     The following is a description further views and representations of the assembled jig assembly  100  and corresponding rotary power tool ( 102 ) arrangement. 
     With reference to  FIG. 3 , a rear-oriented exploded view of the jig assembly  100  is shown, with the rear support  110  with mounting screws  112  visible within the buffer mount  117  within the lower receiver  116 . In an embodiment the carriage plates  114  and/or  302  can define a thickness TC 3  of approximately ½ inch (+⅛ inch). This dimension is highly variable in alternate embodiments an, in part, facilitates the formation or female-threaded holes for receiving screws  106 . Note that, while two carriage plates are employed in the depicted embodiment, at least one carriage plate can be used in alternate arrangements. Such a single plate can include appropriate brackets or other structures to maintain it in confronting, accurate engagement with the lower receiver side. 
     With reference to  FIG. 4  a rear view of the assembled jig  100  is shown in operation on the lower receiver  116 . The carriage plates  114 ,  302  are situated on their respective sides of the lower receiver  116  and are held in place by removable pins  306  and  704 . Each of the pins is removably locked in place by a detent  307  located at one end and a ring  309  at the other. Opening  402  in the tool mount  103  serves to provide air circulation within the area of the machining, a portal for the egress of machining debris and a visible window to allow a view of the machining in process. 
       FIG. 5  is an exploded left side view of the jig  100  in an assembled state, with a rotary power tool  102 , a rotary power tool adapter  122 , a rotary tool  104 , a guide plate  108 , a rear support  110 , a left carriage  302 , a lower receiver  116 , a front support  118  and related mechanisms. The buffer mount  117  protrudes through guide plate  108 . Plates  108  and  122  support the rotary power tool above the lower receiver  116  such that the rotary power tool is not resting upon the lower receiver. 
     As described above, the left carriage plate  302  is also provided with three drill guide holes,  632 ,  634 ,  636 , for the location of and drilling of pivot/pin holes into the lower receiver  116  that are aligned with the right carriage holes  132 ,  134  and  136 , respectively and define the same dimensions. In embodiments in which a pin/pivot defines different diameters on each side, or is eccentric the diameter or placement of the left carriage hole can vary relative to that of the right carriage hole. 
       FIG. 6  is a collapsed view of  FIG. 5  illustrating; a rotary power tool  102 , a rotary power tool adapter  122 , a guide plate  108 , a left carriage  302 , a lower receiver  116  and a front support  118 . 
       FIG. 7  is an exploded front view of the illustrative jig  100 . Pin  704  is positioned to be inserted through takedown pin mounts  702 , such that the pin  704  passes through the front support  118  and the pin mounts  702 , thereby locking the front support  118  to the lower receiver  116 . The pin mounts are through holes in the lower receiver  116 . In another embodiment, pins  306  and  704  can define a bolt with a removable nut for locking the bolt in place. 
       FIG. 8  is a collapsed view of the jig  100  with particular attention called to the placement of the locating pins  306 ,  704  in the pin mounts  702  and are held in place by detents  307 . The locating pin  306  is removable and is situated in a location along the front and rear takedown pin holes of a firearm receiver that is not threaded and is provided with at least one of a pull, a string or other handle for firearm lower receiver manufacturing. 
       FIG. 9  is a bottom view of the jig  100 . The bottom surface of adapter  122  includes a plurality of wells  901  of various sizes, angles and shapes disposed across the surface of the adapter  122 . A rotary power tool support bearing  902  is inserted into the rotary power tool adapter  122  (for example—using a press or other biasing device) in a circular well  901  located near the center point of the adapter  122 . Bearing  902  allows movement of a rotary power tool which further supports the rotary tool, thereby increasing rigidity, user control, and thus, quality. The rotary tool  104  is then inserted into the rotary tool support bearing  902  and the rotary power tool adapter  122  is connected to the rotary power tool  102  by inserting adapter screws  906  into their respective wells  901  in the adapter  122  and tightened into adapter  103 . The guide pins  908  are connected to the adapter  122  by inserting an adapter screw  904  through the guide pins  908  and tightened into the adapter plate. The above thus defines the components of the tooling assembly. 
     In use, the rotary power tool  102  and mount  103  and adapter  122  are placed on top of the guide plate  108  and assembled, as described above, to form the jig. The guide pins  908  are placed into the guide cavities  1202  located within the guide plate  108 . The rotary tool  104  protrudes by a predetermined length from adapter  122  so as to interface with the lower receiver  116  situated below guide plate  108 . The geometry of the walls of the lower receiver are generally vertical, with the walls of each side parallel to each other up and down and front to back. This geometry provides an opportunity for the unskilled user to complete the machining of the receiver and the performance of the machining tools is optimized by the stability of the jig. The rotary power tool  102 , adapter  122 , rotary tool  104 , guide pins  908 , and connecting screws  904  and  906 , are then guided within the guide cavities  1202 . The location of the guide pins  908  and guide cavities  1202  are placed as to locate the rotary tool  104  in a predetermined location within the lower receiver  116  to achieve the desired results without placing the rotary tool  104  in direct contact with any components other than the lower receiver  116 , thus reducing premature wear. Window  920  is a cutout slot at the rear of adapter  122  and provides visual and physical access to the lower receiver during machining operations, as well as preventing contact with the buffer mount  117 . 
       FIG. 10  is a collapsed view of  FIG. 9  showing the protrusion of the rotary tool  104 . Window  920  is aligned to the rear of the jig. 
       FIG. 11  is a top view of the jig  100  without the rotary power tool. Indices  1102 ,  1104 ,  1106  are located along a surface of guide plate  108  and are depth references for the end milling process. Each of the indices is a cavity, as shown in  FIG. 1 . Indices  1102 ,  1104  and  1106  relate to three different lengths for guide pins and the guide cavities are stepped at three different heights so that as the pins get longer, the guide describes a smaller area. The alignment of the view of  FIG. 11  is that the top of the view is the front of the jig and the bottom of the view corresponds to the rear of the jig. Buffer mount  117  is depicted as protruding through guide plate  108 . 
       FIG. 12  is the same view as  FIG. 11  with the rotary power tool adapter viewed as semi-transparent, allowing a better view of a rotary tool  104 , a guide plate  108  incorporating guide cavities  1202 ; a lower receiver  116  and guide pins  908  residing within their respective wells  901 . The shape of the guide cavities  1202  corresponds to the shape of the internal walls of the lower receiver  116  such that when the rotary tool  104  is inserted into the lower receiver  116 , the operator maneuvers the guide pins  908  against the walls of the guide cavities  1202  and can accurately machine the internal surfaces of the lower receiver  116 . 
     In operation, the user places carriages  114  and  302  in a vise or other clamping device to hold steady. The protrusion depth of the rotary tool  104  is set using indices  1102 ,  1104 ,  1106 . In practice, this is done by placing rotary tool  104  within the indices and aligning to the appropriate hash mark for the required milling step and moving the rotary power tool adapter  122  into contact with the edge of guide plate  108  therefore setting the protrusion depth to the appropriate hash mark relative to the bottom surface of adapter  122   
     The assembled rotary power tool  102 , mount  103 , rotary tool  104 , adapter  122  and guide pins  908  are engaged with the guide plate  108  and guide cavities  1202 . When the assemblies are placed atop each other with guide pins  908  within guide cavities  1202  the rotary power tool is switched on and rotary tool  104  begins to rotate at a high rate of angular velocity. The user grasps either the rotary power tool  102 , mount  103  or adapter  122  and slide the adapter  122  along the guide plate  108 . The protruding guide pins  908  contact the walls of the guide  1202  preventing rotary tool  104  from milling into the incorrect locations. This task is continued until guide pins  908  have been translated through the entire guide cavities  1202  removing all the material that rotary tool  104  has contacted within the lower receiver  116 . The rotary power tool  102  is then switched off and the rotary tool  104  is allowed to come to rest. The assembled rotary power tool  102 , mount  103 , rotary tool  104 , adapter  122  and guide pins  908  are then lifted off of the guide plate  108 . The rotary tool  104  is then placed back into indices  1102 ,  1104 ,  1106  to adjust the protrusion depth to the next hash mark of the respective index. When the depth is properly set, the assembled rotary power tool  102 , mount  103 , rotary tool  104 , adapter  122  and guide pins  908  are re-engaged with guide plate  108  and guide cavities  1202 . The same procedure is followed to remove this material with rotary tool  104  from lower receiver  116 . This procedure is similarly followed until all material is removed from lower receiver  116 . Chips can be removed periodically during each cutting task using a vacuum or by rotating the receiver and jig assembly upside down. 
     In order to guide rotary  104  properly in lower receiver  116  to allow for proper function, guide cavities  1202  have additional cavities contained within them. For example, the entire guide cavity  1202  is milled to a depth greater than 1/16 inch but less than ⅛ inch. A further reduced area within guide cavity  1202  is milled to a depth greater than ⅛ but less than 3/16 inch. Yet another area within the reduced area is milled to a depth greater than 3/16 inch. This allows for two reduced area cavities within the larger guide cavity  1202 . Guide pins  908  can be interchanged with varying lengths to allow for the assembled rotary power tool  102 , mount  103 , rotary tool  104 , adapter  122  and guide pin  908  unit to be engaged in either the full guide cavities  1202  or within the reduced area cavities within guide cavities  1202 . If a guide pin  908  has a length greater than zero but less than ⅛ of an inch, it would guide within the entire guide cavities  1202 . If a guide pin  908  has a length greater than ⅛ but less than 3/16 of an inch, similarly it would guide within the reduced area within the guide cavities  1202 . Finally, if a guide pin  908  has a length greater than 3/16 of an inch it would be guided within the cavity within the reduced area cavity which is within the guide cavities  1202 . With this arrangement, the assembled rotary power tool  102 , mount  103 , rotary tool  104 , adapter  122  and guide pins  908  can guide the rotary tool  104  to various shapes within the lower receiver by interchanging the guide pins  908  length. 
       FIGS. 13-19  depict various methods with reference to  FIGS. 20-27 . 
       FIG. 13  depicts a method  1300  of jig assembly according to one or more aspects of the disclosure. 
     At block  1302 , and with reference to  FIGS. 21A-B , thread the buffer adapter  7  into lower receiver. The buffer adapter  7  should sit just below surface of the lower receiver with threaded holes sitting horizontal. If the buffer adapter  7  is difficult to thread, #8-32 screws  15  can be installed for leverage. 
     At block  1304 , and with reference to  FIGS. 21C-D , orient side plates  3 ,  4  on each side of the lower receiver, taking note of right and left as it would be oriented in a shooting position. Insert long quick release pin  10  through right side plate, through receiver rear takedown, and out left side. 
     At block  1306 , and with reference to  FIGS. 21E-F , place the drill guide  2  between side plates as shown and align screw holes. It should align only one way. Pinch side plates against drill guide and tighten four #8-32 screws  15 . 
     At block  1308 , and with reference to  FIGS. 21G-H , use 3/16″ Allen wrench to thread ¼-20×2″ screw  13  through left side plate  4  and into right plate  3  using care not to cross-thread. 
     At block  1310 , and with reference to  FIGS. 21I-J , align the front takedown adapter  8  between front takedown holes. Push the short quick release pin  11  through receiver and adapter as shown. 
     At block  1312 , and with reference to  FIGS. 21K-L , place the guide plate  1  atop side plates  3 ,  4  as shown. Align screw holes on guide plate  1  with buffer adapter  7  screw holes. Thread two #8-32 screws  15  and leave loose. 
     At block  1314 , and with reference to  FIGS. 21M-N , align front takedown adapter  8  (not shown) with holes in guide plate  1 . Insert and tighten two #8-32 screws  15 , tightening each screw a little at time. Now, tighten two #8-32 screws  15  from blocks  1302 - 1312 . The buffer adapter  7  will self-center in buffer mount. Guide plate  1  may move as these are tightened. Allow guide plate to move freely during tightening. 
     At block  1316 , and with reference to  FIGS. 21O-P , loosely thread six ¼-20×½″ screws  14  through guide plate  1  and into side plates  3 ,  4 . Tighten screws using 3/16″ Allen wrench. The jig assembly is now complete. 
       FIG. 14  depicts a method  1400  of drilling with a jig assembly according to one or more aspects of the disclosure. 
     At block  1402 , and with reference to  FIG. 22A , slide ⅜″ drill stop onto shank of ⅜″ drill bit. Insert drill bit to full depth of depth gauge #2  1104 . Place the drill stop against the edge of the guide plate  1 . Secure drill stop onto drill bit. 
     At block  1404 , and with reference to  FIGS. 22B-C , spray WD-40 into hole #2 of the drill guide  2 . Insert ⅜″ drill bit into hole. Do not start drill until bit is fully inserted. Start drill and apply firm pressure. Periodically, lift drill to assist in chip removal. Reapply WD-40 as necessary. Stop drilling just before the drill stop touches the drill guide  2 . 
     At block  1406 , and with reference to  FIGS. 22D-E , prior to drilling, ensure that jig assembly is level. Spray WD-40 into hole #3 of drill guide  2 . Insert 5/16″ drill bit into hole. Do not start drill until bit is fully inserted. Start drill and apply firm pressure. Periodically, lift drill to assist in chip removal. Reapply WD-40 as necessary. Stop drilling when the drill bit exits the bottom of the fire control pocket. Take care not to drill into the trigger guard. In this example, keep the drill bit perpendicular to the lower receiver. Drilling at a large angle can result in an oblong trigger slot. 
     At block  1408 , and with reference to  FIGS. 22F-G , remove four #8-32 screws  15  and remove the drill guide  2 . It may be necessary to loosen the vise and/or use a screwdriver to gently pry the drill guide from between the side plates. Insert the screw driver shank into hole #2 and gently pry upward. 
     At block  1410 , and with reference to  FIGS. 22H-I , remove long quick release pin  10  from rear takedown hole. 
       FIG. 15  depicts a method  1500  of milling with a jig assembly according to one or more aspects of the disclosure. 
     Initially, prepare your router for milling by installing the universal router adapter  5 . If using a variable speed router, start router on slowest speed and gradually increase speed until optimal milling results are achieved. Generally speaking, this will equate to speed “2” to speed “4” on most variable models with “1” to “10” speed adjustments. Do not insert or remove router while it is spinning. Move router smoothly in a clockwise manner, do not mill in straight lines for extended periods. Avoid abruptly pulling the end mill or exerting excessive force to move the end mill. Apply WD-40 liberally while milling to reduce excess heat. Remove chips whenever necessary. 
     At block  1502 , and with reference to  FIGS. 23A-B , install #1 (short) guide pins  9  on router adapter  5  using the two smallest socket cap screws and 7/64″ Allen wrench. Open end of pins should be facing up. Make sure pin seats are clear of debris prior to installing. Check that guide pins are properly seated. 
     At block  1504 , and with reference to  FIG. 23C , set end mill depth to the first hash mark using depth gauge #1  1102 . Set depth by holding base of router adapter  5  against the edge of the guide plate  1 . Be sure guide pins  9  are not between adapter and guide plate. Make sure router depth adjustment is locked when complete. 
     At block  1506 , and with reference to  FIG. 23D , orient lower receiver assembly so the buffer extension is closest to the user. Place router assembly atop guide plate  1 , with end mill entering the earlier drilled ⅜″ hole. The notched side of the router adapter should be facing the buffer extension as shown. The guide pins should be positioned inside the guide cavities on both sides. Turn router on slowest speed and increase to operating speed once ready to mill. Mill using consistent pressure and speed, moving in a clockwise manner. 
     At block  1508 , and with reference to  FIG. 23E , make the first pass of milling allowing the guide pins to follow the entire area of the guide cavities. When milling corners, gently twist the router side to side to assist to complete the entire corner radius. 
     At block  1510 , and with reference to  FIG. 23F , once the entire pass has been milled to depth, set end mill depth to the second hash mark. Mill second pass following the same method and process as shown in blocks  1506 - 1508 . 
     At block  1512 , and with reference to  FIGS. 23G-I , continue milling in this manner, adjusting end mill depth by 1 hash mark until you reach the final hash mark of depth gauge #1. Do not attempt to mill more than 1 hash mark, as it may result in poor quality, longer time and broken end mills. 
     At block  1514 , and with reference to  FIGS. 23J-K , complete the final pass to full depth of depth gauge #1 and stop. Before continuing to depth gauge #2, the #2 (medium) guide pins  9  should be installed. 
       FIG. 16  depicts a method  1600  of milling with a jig assembly according to one or more aspects of the disclosure. 
     At block  1602 , and with reference to  FIGS. 24A-B , remove #1 (short) guide pins  9  and install #2 (medium) guide pins  9  on router adapter  5  reusing the (2) screws and 7/64″ allen wrench. Make sure pin seats are clear of debris prior to installing. Check that guide pins are properly seated. 
     At block  1604 , and with reference to  FIG. 24C , set end mill depth to the first hash mark using depth gauge #2. Set depth by holding base of router adapter  5  against the edge of the guide plate  1 . Be sure guide pins are not between adapter and guide plate. Make sure router depth adjustment is locked when complete. 
     At block  1606 , and with reference to  FIG. 24D , place router assembly atop guide plate  1 , with end mill entering the earlier drilled ⅜″ hole. The guide pins  9  should be positioned inside the #2 guide cavities on both sides. Turn router on slowest speed and increase to operating speed once ready to mill. Mill using consistent pressure and speed, moving in a clockwise manner. 
     At block  1608 , and with reference to  FIG. 24E , complete the first pass allowing the guide pins  9  to follow the #2 guide cavities. When milling corners, gently twist the router side to side to assist to complete the entire corner radius. 
     At block  1610 , and with reference to  FIG. 24F , once the entire pass has been milled, set end mill depth to the second hash mark. Mill second pass following the same method and process as outlined in blocks  1606  and  1608 . 
     At block  1612 , and with reference to  FIGS. 24G-I , continue milling in the same manner, adjusting milling depth by 1 hash mark until you reach the final hash mark of depth gauge #2. Do not attempt to mill more than 1 hash mark, as it may result in poor quality, longer time and broken end mills. 
     At block  1614 , and with reference to  FIGS. 24J-K , complete the final pass to full depth of depth gauge #2. Start the end mill in the 5/16″ pilot hole. Start the router at slowest speed setting and mill the hole larger before increasing the router speed. Once complete, stop. Before continuing to depth gauge #3  1106 , the #3 (long) guide pins  9  should be installed on the router adapter. 
       FIG. 17  depicts a method  1700  of milling with a jig assembly according to one or more aspects of the disclosure. 
     At block  1702 , and with reference to  FIGS. 25A-B , remove #2 (medium) guide pins  9  and install #3 (long) guide pins  9  on router adapter  5  reusing the (2) screws and 7/64″ Allen wrench. Open end of pins should be facing up. Make sure pin seats are clear of debris prior to installing. Check that guide pins are properly seated. 
     At block  1704 , and with reference to  FIG. 25C , set end mill depth using depth gauge #3. Set depth by holding base of router adapter  5  against the edge of the guide plate  1 . Be sure guide pins are not between adapter and guide plate. Make sure router depth adjustment is locked before when complete. 
     At block  1706 , and with reference to  FIGS. 25D-E , place router on guide plate  1 , with end mill entering the earlier drilled 5/16″ hole. The guide pins  9  should be positioned inside the #3 guide cavities on both sides. Start the router at slowest speed setting and mill the hole larger before increasing the router speed. Gently mill in a clockwise manner until the trigger slot is formed. 
       FIG. 18  depicts a method  1800  of drilling with a jig assembly according to one or more aspects of the disclosure. 
     At block  1802 , clamp jig assembly in the vise by the guide plate  1  so right side plate is facing up and ensure that the assembly is level. Use a rag or cardboard between the vise and guide plate to prevent damage to the top surface of the guide plate. 
     At block  1804 , and with reference to  FIG. 26A , spray WD-40 into large hole. Insert ⅜″ drill bit into large guide hole (large left hole as shown). Do not start drill until bit is fully inserted in the guide hole. Apply moderate pressure and drill until the bit penetrates the right side wall. Do not drill through both sides. 
     At block  1806 , and with reference to  FIGS. 26B-C , spray WD-40 into both small holes. Insert 19/64″ drill bit into either remaining guide holes. Do not start drill until bit is fully inserted in the guide hole. Apply moderate pressure and drill until the bit penetrates the right side wall. Do not drill through both sides. Repeat in last remaining hole. 
     At block  1808 , unclamp jig assembly from vise and flip it over so the left side plate is facing up and re-clamp by the guide plate  1 . Ensure that assembly is level. Use a rag or cardboard between the vise and guide plate to prevent damage to the top surface of the guide plate. 
     At block  1810 , and with reference to  FIGS. 26D-E , spray WD-40 into both small holes. Insert 19/64″ drill bit into either small guide hole. Do not start drill until bit is fully inserted in the guide hole. Apply moderate pressure and drill until the bit penetrates the left side wall. Continue drilling so the bit passes through the opposite side wall connecting the holes from either side. Repeat on remaining small hole. 
     At block  1812 , and with reference to  FIGS. 26F-G , spray WD-40 into large hole. Insert ⅜″ drill bit into large guide hole. Do not start drill until bit is fully inserted in the guide hole. Apply moderate pressure and drill until the bit penetrates the right side wall. Continue drilling so the bit passes through the opposite side wall connecting the holes from either side. 
       FIG. 19  depicts a method  1900  of lower receiver removal using a jig assembly according to one or more aspects of the disclosure. 
     One advantage of the presently described jig assembly or assemblies is they do not require the user to completely disassemble the jig assembly to remove or mount an 80% lower receiver. 
     At block  1902 , and with reference to  FIG. 27A , remove two #8-32 screws  15  from the buffer adapter  7 . 
     At block  1904 , and with reference to  FIG. 27B , remove short quick release pin  11  from front takedown adapter. 
     At block  1906 , and with reference to  FIG. 27C , remove ¼-20×2″ screw from left side plate  4  using 3/16″ Allen wrench. 
     At block  1908 , and with reference to  FIG. 27D , the jig assembly and lower receiver should now be separable. For the AR-308 router jig, loosening or removing one of the side plates  3 ,  4  may be employed to extract the lower receiver. 
     At block  1910 , and with reference to  FIG. 27E , unthread the buffer adapter  7  from the lower receiver. 
       FIG. 20  depicts various components of a jig assembly with reference to  FIGS. 13-19 and 21-27 , as described below: 
       1 . Guide Plate (e.g. guide plate  108  described above);  2 . Drill Guide;  3 . Right Side Plate (e.g., carriage  114  as described above);  4 . Left Side Plate (e.g., carriage  302  as described above);  5 . Router Adapter (e.g., power tool adapter  122 );  6 . Router Adapter Side Block;  7 . Buffer Adapter (e.g., rear support  110  as described above);  8 . Front Takedown Adapter (e.g., front support  118 );  9 . Guide Pin Set (e.g.,  908  as described above);  10 . Long Quick Release Pin (e.g., corresponding to locating pin  306 );  11 . Short Quick Release Pin (e.g., corresponding to pin  704 );  12 . (5) M4×10 Phillips Truss Screw (e.g., adapter screw  906  as described above);  13 . (1) ¼″-20×2″ Socket Screw (e.g., carriage screw  304  as described above);  14 . (6) ¼″-20×⅝″ Socket Screws (e.g., plate screws  106  as described above);  15 . (8) #8-32×⅝″ Phillips Screws (e.g., plate screws  120  as described above). 
     It should be clear that the above-described jig for manufacturing a firearm lower receiver is a universal fitment and facilitates in the guidance of the rotary tool without placing the rotary tool in direct contact with any of a plurality of guidance features for firearm lower receiver manufacturing. It is straightforward to use, resists wear and produces accurate and repeatable results in the hands of both skilled and unskilled users. 
     The foregoing has been a detailed description of illustrative embodiments of the invention. Various modifications and additions can be made without departing from the spirit and scope if this invention. Each of the various embodiments described above may be combined with other described embodiments in order to provide multiple features. As used herein the directional terms, such as, but not limited to, “up” and “down”, “upward” and “downward”, “rear”, “rearward” and “forward”, “top” and “bottom”, “inside” and “outer”, “front” and “back”, “inner” and “outer”, “interior” and “exterior”, “downward” and “upward”, “horizontal” and “vertical” should be taken as relative conventions only, rather than absolute indications of orientation or direction with respect to a direction of the force of gravity. Furthermore, while the foregoing describes a number of separate embodiments of the apparatus and method of the present invention, what has been described herein is merely illustrative of the application of the principles of the present invention. For example, the foregoing jig can be adapted to machining and finishing other parts for a firearm, such as portions of an upper receiver that is being repaired, modified or fabricated. Moreover, the jig can be sold as part of a kit with additional right and left carriages and guide pins that are adapted for machining other firearms (for example, polishing the internal surfaces or repairing a restored firearm). This jig can be adapted for firearms of various sizes and shapes by interchanging the carriages, thereby providing a jig that can be useful to a person finishing a firearm, and repairing and/or restoring a firearm. Also, it is expressly contemplated that the size and shape of the plates of the jig can vary. In general, they are sized in an embodiment proportionally to the depiction herein relative to the size of the lower receiver. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention.