Abstract:
An electric case trimmer assembly utilizes an inexpensive case adapter bearing to adapt for each size case. The case trimmer assembly includes an end mill for cutting excess material from the case. The end mill is fixed to a micrometer dial threadedly engaging a barrel. The case adapter bearing is fixed to the barrel. The micrometer dial is rotated to adjust the position of the end mill with respect to the case adapter bearing to precisely adjust the amount of material cut from the case. The case adapter bearing is easily changed to trim different cases.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to trimming ammunition cases and in particular to a motorized adjustable precision micrometer case trimmer. 
     Ammunition cases are generally the most expensive component of ammunition. Many shooting enthusiasts reuse the cases to save money. While such cases may be capable of multiple uses, some cases, especially expensive high power rifle cases, are stretched in each use. When the cases are stretched, the neck of the case (the portion a bullet is seated in), becomes longer and increases the contact surface with bullet, and affects the release of the bullet when the ammunition is filed. Such changes in the release affect the velocity, and thus the consistency of the bullet at long range. 
     To address the case stretching, the cases are often trimmed back to the original length. Both manual and electric trimmers are known. Unfortunately, the known electric trimmers require expensive separate components for each size case. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by providing an electric case trimmer assembly which utilizes an inexpensive case adapter bearing to adapt for each size case. The case trimmer assembly includes an end mill for cutting excess material from the case. The end mill is fixed to a micrometer dial threadedly engaging a barrel. The case adapter bearing is fixed to the barrel. The micrometer dial is rotated to adjust the position of the end mill with respect to the case adapter bearing to precisely adjust the amount of material cut from the case. The case adapter bearing is easily changed to trim different cases. 
     In accordance with one aspect of the invention, there is provided an electric case trimmer assembly having a micrometer cutting adjustment. A first cut is made intentionally leaving the case longer than intended. The case is measured, and the micrometer dial is turned a pre-determined number of lines to precisely adjust the case trimmer to trim the case to the correct length. 
     In accordance with another aspect of the invention, there is provided a method according to the present invention. The method includes installing a case adapter bearing for a selected case type into a barrel of the case trimmer assembly, turning a micrometer dial of the case trimmer assembly counter clockwise until a stop is reached, turning the micrometer dial of the case trimmer assembly clockwise to align a micrometer dial mark with a first barrel mark, attaching the case trimmer assembly to a drill motor, with the drill motor running, inserting a case of the selected case type into the case trimmer assembly against an end mill of the case trimmer assembly, trimming excess material from the case, removing the trimmed case from the case trimmer assembly, measuring the length of the trimmed case, turning the micrometer dial clockwise to adjust the position of the end mill with respect to the case adapter bearing, with the drill motor running, inserting a case of the selected case type into the case trimmer assembly, and trimming excess material from the case. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1  is a side view of a case trimming assembly according to the present invention. 
         FIG. 2  is a cross-sectional view of the case trimming assembly according to the present invention taken along line  2 - 2  of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the case trimming assembly according to the present invention separated into major components taken along line  2 - 2  of  FIG. 1 . 
         FIG. 4  is a side view of the case trimming assembly according to the present invention with a case ready for insertion into the case trimming assembly. 
         FIG. 5  is a side view of the case trimming assembly according to the present invention with the case in the case trimming assembly. 
         FIG. 6  is a cross-sectional view of the case trimming assembly according to the present invention with the case in the case trimming assembly taken along line  6 - 6  of  FIG. 5 . 
         FIG. 7  is a side view of the case trimming assembly according to the present invention attached to a drill motor. 
         FIG. 8A  is a side view of the case trimming assembly according to the present invention with the case in the case trimming assembly for a first cut before precision adjustment. 
         FIG. 8B  is a side view of the case trimming assembly according to the present invention with the case in the case trimming assembly for second and latter cuts after precision adjustment. 
         FIG. 9  is a method according to the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
     A side view of a case trimming assembly  10  according to the present invention is shown in  FIG. 1 , a cross-sectional view of the case trimming assembly  10  taken along line  2 - 2  of  FIG. 1  is shown in  FIG. 2 , and a cross-sectional view of the case trimming assembly  10  separated into major components taken along line  2 - 2  of  FIG. 1  is shown in  FIG. 3 . The case trimming assembly  10  includes a micrometer dial  12  (or end mill holding portion), a barrel  14  (or case guiding portion), a case adapter bearing  18 , and an end mill  16 . The end mill  16  is fixedly attached to the micrometer dial  12  using a set screw  17  and the case adapter bearing  18  is fixedly attached to the barrel  14  by a set screw  19 . The end mill  16  includes a cutting face  16   a  for trimming cases. The end mill  16  and case adapter bearing are coaxial with the micrometer dial  12 . 
     The barrel  14  threadedly engages the micrometer dial  12  by threads  20   a  and  20   b , and a third set screw  13  engages a notched ring  22  of the barrel  14 . The end mill  16  is fixedly attached to the micrometer dial  12  and turning the micrometer dial  12  on the barrel  16  advances and retreats the end mill  16  with respect to the barrel  14 . The case adapter bearing  18  includes an outer race  18   a  fixedly attached to the barrel by the set screw  19  and a rotating inner race  18   b  having an inner case contour  18   c . The inner case contour  18   c  is configured for one or more cases  30  (see  FIG. 4 ) and limits the distance a case  30  can be inserted into the barrel  14 . The set screw  13  serves two purposes. The set screw  13  is tightened against the barrel  14  to fix the position of the micrometer dial for repeated trimming, and during adjustment, the set screw  13  contacts sides of the notched ring  22  to limit adjustment of the micrometer ring  12  on the barrel  14 . 
     A side view of the case trimming assembly  10  with a case  30  ready for insertion into the case trimming assembly  10  is shown in  FIG. 4 , a side view of the case trimming assembly  10  with the case  30  in the case trimming assembly  10  is shown in  FIG. 5 , and a cross-sectional view of the case trimming assembly  10  with the case  30  in the case trimming assembly  10  taken along line  6 - 6  of  FIG. 5  is shown in  FIG. 6 . Windows  24  allow viewing the contact of case  30  with the end mill  16  and allows trimmed material to escape from the barrel  14 . The case  30  is manually inserted by a user until the case  30  rests against the inner case contour  18   c  of the case adapter bearing  18 . When the case mouth  30   a  encounters the end mill cutting face  16   a  before the case  30  is seated against the inner case contour  18   c , material is cut from the case mouth  30   a  until further advance of the case  30  into the barrel is stopped by the inner case contour  18   c.    
     A side view of the case trimming assembly  10  attached to a drill motor  40  is shown in  FIG. 7 . The entire case trimming assembly  10 , with only the exception of the rotating inner race  18   b  of the case adapter bearing  18 , is rotated by the drill motor  40 . The user holds the case  30  and inserts the case  30  into the rotating case trimming assembly  10 . 
     A side view of the case trimming assembly  10  with the case  10  in the case trimming assembly  10  for a first cut before precision adjustment is shown in  FIG. 8A  and a side view of the case trimming assembly  10  with the case  30  in the case trimming assembly  10  for second and later cuts after precision adjustment is shown in  FIG. 8B . The first cut is made with the micrometer dial turned counter clockwise as far as possible, but turned back clockwise to align a dial mark  12   a  with a closest barrel mark  14   a . There is preferably a single dial mark  12   a  and preferably a multiplicity of evenly spaced apart barrel marks  14   a . The number of barrel marks may vary, but a relationship between the angular spacing of the barrel marks  14   a  and the threads  20   a  and  20   b  (see  FIG. 3 ) is preferably known and used as a basis for adjusting the micrometer dial  12  on the barrel  14 . For example, in a preferred embodiment, turning the micrometer dial  12  to align the dial mark  12   a  with and adjacent barrel mark  14   a , advances or retreats the micrometer dial  12  0.002 inches on the barrel  14 . 
     After making a first cut, the length of the trimmed case  30  is measured, and the micrometer dial is adjusted on the barrel to provide the desired precision cut. 
       FIG. 9  is a method according to the present invention. The method includes installing a case adapter bearing for a selected case type into a barrel of the case trimmer assembly at step  100 , turning a micrometer dial of the case trimmer assembly counter clockwise until a stop is reached at step  102 , turning the micrometer dial of the case trimmer assembly clockwise to align a micrometer dial mark with a first barrel mark at step  104 , attaching the case trimmer assembly to a drill motor at step  106 , with the drill motor running, inserting a case of the selected case type into the case trimmer assembly against an end mill of the case trimmer assembly at step  108 , trimming excess material from the case at step  110 , removing the trimmed case from the case trimmer assembly at step  112 , measuring the length of the trimmed case at step  114 , turning the micrometer dial clockwise to adjust the position of the end mill with respect to the case adapter bearing at step  116 , with the drill motor running, inserting a case of the selected case type into the case trimmer assembly at step  118 , and trimming excess material from the case at step  120 . 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.