Abstract:
An automatic optical center punch adapted to perform with high accuracy and ease of use is disclosed. The punch includes a spring-loaded hammer and a rotational latch mechanism. The rotational latch mechanism restrains the movement of the hammer to allow the spring to be compressed when pressure is initially applied to the punch by its operator. When the spring is fully compressed, the latch mechanism engages a cam surface, which causes the latch to rotate to release the hammer. The spring-loaded hammer makes contact with a punch head assembly, which causes perforation of the work surface to take place. Once the hammer has been extended by the spring, the latch engages a second cam surface, which causes the latch to rotate in the opposite direction to restrain the hammer in preparation for the next compression of the spring.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of the filing date of corresponding U.S. Provisional Patent Application No. 60/400,760, entitled “OPTICALLY ALIGNED CENTER PUNCH WITH INTEGRAL DOUBLE ACTION STRIKER,” filed Aug. 2, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Technical Field  
           [0003]    The present invention is related generally to machinists&#39; tools. More specifically, the present invention is directed toward an optically-aligned center punch with an automatic striker mechanism.  
           [0004]    2. Description of Related Art  
           [0005]    Because standard, multi-flute twist drills are somewhat flexible and do not cut well at the end point, some means of starting a hole at a desired location is necessary to prevent the drill bit&#39;s drifting away from the intended placement. One method of starting holes is to place the point of a sharp object at the intended hole location and strike the object with a hammer to drive the point into the material leaving a small dimple at the intended hole location. A sharp object used for such a purpose is normally called a center punch.  
           [0006]    Center punches of the style shown in FIG. 1 have existed for over one hundred years and are acceptable for low and medium precision work. The obtuse angle of the point limits the user&#39;s view of the point while aligning the punch to any desired location markings making accurate placement of the punch difficult. As shown in FIG. 1, the angle of the punch relative to the work surface, the angle of the hammer face relative to the punch, and the angle of the tangent to the arc followed by the hammer at its point of impact with the punch relative to both the punch and the work surface all affect the motion of the punch into the work surface and, therefore, the placement accuracy of the final punch mark.  
           [0007]    The alignment fixture shown in FIG. 2 alleviates some of the problems of the basic center punch by holding the punch perpendicular to the work. An optical sighting device the same diameter as the punch can be used to place the fixture with a relatively high degree of accuracy, but since the hammer is still wielded manually, the accuracy of the final punch mark is often no better than that which can be achieved without the fixture.  
           [0008]    Adding a narrow shaft to the basic center punch allows the use of an annular weight as a slide hammer for striking the punch as shown in FIG. 3. This arrangement ensures close alignment of the hammer&#39;s impact with the axis of the punch and, when used in conjunction with the alignment fixture of FIG. 2, can be used to place punch marks with a relatively high degree of positional accuracy, but only on horizontal surfaces. Devices which use smaller slide hammers driven by springs allow use on non-horizontal surfaces but require two hands to operate and are, therefore, difficult to use with an alignment fixture.  
           [0009]    A more modern center punch with integral, double action striker is shown in FIGS.  4 A- 4 C. This device (commonly called an “automatic center punch”) requires only one hand to operate because pressing the body of the punch toward the work first compresses a spring against the striker and then releases the striker to impact the punch. This device addresses the two handed operation problem of the spring operated slide hammer punch but at the expense of some loss of accuracy due to the clearances required by the rocking motion of its latch mechanism.  
           [0010]    Thus, a need exists for a center punch that allows for convenience of use in a variety of environments and applications, while maintaining a high level of accuracy.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention is directed toward an automatic optical center punch adapted to perform with high accuracy and ease of use. The punch includes a spring-loaded hammer and a rotational latch mechanism. The rotational latch mechanism restrains the movement of the hammer to allow the spring to be compressed when pressure is initially applied to the punch by its operator. When the spring is fully compressed, the latch mechanism engages a cam surface, which causes the latch to rotate to release the hammer. The spring-loaded hammer makes contact with a punch head assembly, which causes perforation of the work surface to take place. Once the hammer has been extended by the spring, the latch engages a second cam surface, which causes the latch to rotate in the opposite direction to restrain the hammer in preparation for the next compression of the spring.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0013]    [0013]FIG. 1 is a diagram of a prior art simple center punch;  
         [0014]    [0014]FIG. 2 is a diagram of a prior art center punch with an alignment fixture;  
         [0015]    FIGS.  3 A- 3 B are diagrams of a prior art center punch with gravity operated slide hammer striker;  
         [0016]    FIGS.  4 A- 4 C are cross-sectional diagrams of a prior art center punch with integral, double action striker in the three critical positions during use;  
         [0017]    [0017]FIG. 5 is a diagram of an alignment fixture in accordance with a preferred embodiment of the present invention;  
         [0018]    [0018]FIG. 6 is a diagram of an optical alignment sight in accordance with a preferred embodiment of the present invention;  
         [0019]    [0019]FIG. 6A is a diagram providing a close up of a spacer ring in FIG. 6;  
         [0020]    [0020]FIG. 7 is a cross-sectional diagram of a center punch with integral, double action striker in accordance with a preferred embodiment of the present invention;  
         [0021]    FIGS.  8 - 15  are diagrams of components of the punch shown in FIG. 7;  
         [0022]    [0022]FIGS. 16, 16A,  17 - 18 ,  18 A, and  19  depict four phases of the operation of a punch striking mechanism in accordance with a preferred embodiment of the present invention;  
         [0023]    FIGS.  20 - 22  depict, from the perspective of the user, the operation of a center punch made in accordance with a preferred embodiment of the present invention; and  
         [0024]    FIGS.  23 - 24  depict an alternative embodiment of the present invention employing an alignment fixture with a concave surface for engaging work surfaces of various shapes.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    The present invention is directed toward an automatic optical center punch with a double-action striker mechanism for high precision one-handed creation of holes or indentation in the surface of a work piece.  
       USE  
       [0026]    According to a preferred embodiment of the present invention, use of the optically aligned center punch is a two step process. As shown in FIG. 20, the first step is to place optical alignment sight  200  within the bore of the alignment fixture  100  and align alignment fixture  100  with the desired reference point on work piece  2000 . Once alignment fixture  100  is properly positioned, it is held in place either manually or with clamps for the second step of the procedure.  
         [0027]    During this process, a spacer ring  204  around reticle face  202  of the optical alignment sight  200  protects the reticle face from being scratched by small imperfections on the surface of the work piece while keeping the spacing between the reticle face consistent but small to minimize parallax errors during alignment.  
         [0028]    Although the use of spacer ring  204  on optical alignment sight  200  increases the potential for parallax error when aligning alignment fixture  100  to the desired punch point, the narrow viewing range provided by the length of optical alignment sight  200  in relation to its diameter makes the maximum parallax error a fraction of the spacing between the reticle face  202  and the work piece. In practice, the view through such an optical alignment sight makes it easy to align the viewing angle to within a few degrees of vertical and make the parallax error insignificant.  
         [0029]    The second step of the procedure is to remove the optical alignment sight  200  from the alignment fixture  100 , place punch head  310  in the alignment fixture, and press end cap  370  of punch head  310  toward the work piece to actuate punch head  310 &#39;s internal striker mechanism. This second step is shown progressively in FIGS. 21 and 22.  
         [0030]    In an alternative embodiment of the present invention, depicted in FIGS. 23 and 24, a concave alignment fixture  400  is used in conjunction with optical alignment sight  200  to position concave alignment fixture  400  with respect to a location on a work surface that is not flat. In FIGS. 23 and 24, for example, cylindrical work surfaces  2300  and  2400  are shown. As shown in FIGS. 23 and 24, concave alignment fixture  400  allows placement on curved surfaces having a small radius of curvature relative to concave alignment fixture  400 , such as spherical work surface  2300 , or curved surfaces having a large radius of curvature relative to concave alignment fixture  400 , such as work surface  2400 . One of ordinary skill in the art will recognize that concave alignment fixture  400  may be used in conjunction with a wide variety of surfaces and that the application of concave alignment fixture  400  is by no means limited to spherical work surfaces. Moreover, one of ordinary skill in the art will recognize that any of a wide variety of alignment fixture shapes may be utilized in conjunction with an automatic center punch in accordance with the present invention without departing from the scope and spirit of the present invention.  
       ALIGNMENT FIXTURE  
       [0031]    [0031]FIG. 5 shows a basic alignment fixture  100  for use on flat surfaces in conjunction with a center punch made in accordance with a preferred embodiment of the present invention. Alignment fixture  100  includes a bore  101  and work face  102 . Bore  101  should be large enough to admit a useful amount of ambient light, accurately finished within very close tolerance of its nominal diameter and straight. Work face  102  should be smooth and oriented to hold bore  101  in the desired alignment with the work piece when the fixture is held firmly against the work piece. For the illustrated fixture  100 , that means that the work face should be flat and perpendicular to the axis of the bore. Once these two critical features are ensured, the fixture should be shaped for easy manual manipulation and locating. Work face  102  may be covered or coated with an anti skid material to help hold it in place once it is properly located for use.  
       OPTICAL ALIGNMENT SIGHT  
       [0032]    [0032]FIG. 6 is a diagram of an optical alignment sight  200  in accordance with a preferred embodiment of the present invention. Optical alignment sight  200  is used to position the alignment fixture  100  relative to the desired hole location on the work piece. Optical alignment sight  200  is made of an optically transparent material and is placed within bore  101  of alignment fixture  100  prior to use. Shaft  201  of optical alignment sight  200  should be straight and long enough to extend all the way through bore  101  of the alignment fixture  100  and sized to provide a close, but easily sliding cylindrical fit within bore  101 . Reticle face  202  of optical alignment sight  200  should be flat, perpendicular to the axis of shaft  201  and polished. Some form of visual alignment feature such as perpendicular lines intersecting at the alignment point (“cross hairs”) should be scribed, etched or drawn on the reticle face  202 . A narrow, shallow recess  203  is formed around the periphery of reticle face  202  for the application of a thin spacer ring  204  which provides a small but definite space between reticle face  202  and the work piece. The relationship between the reticle face  202 , spacer ring recess  203  and spacer ring  204  is shown more clearly in the enlargement of one edge of the reticle face end of the sight shown in FIG. 6A. The spacer ring  204  is preferably made of an abrasion resistant material and retained by an adhesive. Head  205  of optical alignment sight  200  has a non-critical diameter and should be long enough to protrude beyond the alignment fixture far enough for easy grasping for removal from the alignment fixture once the optical alignment is accomplished. Crown  206  of the sight is preferably radiused and polished to provide some degree of optical magnification of the reticle face and the work piece.  
       CENTER PUNCH  
       [0033]    A cross-section of a center punch  300  with integral, double action striker in accordance with a preferred embodiment of the present invention is shown in FIG. 7. The device consists of a punch head  310 , an anvil  320 , a latch  340 , a latch spring  303 , a latch spring guide  380 , a cam sleeve  350 , a cam sleeve retaining clip  302 , a hammer  360 , a hammer spring  301 , a housing  330  and an end cap  370 .  
         [0034]    Hammer spring  301  is a compression spring which fits around hammer  360  and within the cam sleeve  350 . Hammer spring  360 &#39;s other parameters may be determined by normal spring design procedures to provide the striking energy desired.  
         [0035]    Latch spring  303  fits around latch spring guide  380  and within bore  365  of hammer  360 . Latch spring  303 &#39;s other parameters may be determined by normal spring design procedures to provide enough force to hold latch  340 , anvil  320 , and punch head  310  fully extended when center punch  300  is turned upside down.  
         [0036]    Cam sleeve retaining clip  302  is an expanding, split, circular ring familiar to those skilled in the art and sized to fit securely in groove  337  in housing  330 .  
       CENTER PUNCH PIECES  
       [0037]    Punch head  310 , which is shown in FIG. 8, may be made from standard punch materials using techniques known to those skilled in the art. The body of punch head  310  should be straight, long enough to extend all the way through bore  101  of alignment fixture  100  (FIG. 5) and sized to provide a close, but easily sliding cylindrical fit within bore  101  of alignment fixture  100 . Point  311  of punch head  310  should be concentric with the body of punch head  310 . The standard included angle ( 312 ) for center punches is 90° but other point designs could be made for special purposes. The end of punch head  310  opposite point  311  should be drilled and tapped  313  with a standard thread for attachment to anvil  320  (FIG. 9), but punch head  310  and anvil  320  could be made as a single unit to reduce cost at the expense of easily interchangeable punches.  
         [0038]    Anvil  320 , shown in FIG. 9, is essentially an extension of punch head  310  and can be made of similar material using similar techniques. Shaft  322  of anvil  320  should have a close, easily sliding cylindrical fit in opening  333  at the bottom of housing  330  (FIG. 13) while head  323  of anvil  320  should have a close, easily sliding cylindrical fit in cam sleeve  350  (FIG. 12). Point  321  of anvil  320  is threaded to fit punch head  310  if the two are not made in one piece.  
         [0039]    Latch  340 , shown in side view in FIG. 10 and in top view in FIG. 10A, should be made of similar material to punch head  310  and anvil  320 . Latch base  341  should have a close, easily sliding cylindrical fit in cam sleeve  350 , but with cam pins  342  evenly spaced around the perimeter (three are shown, but the actual number is not critical) which extend into cam slots  353  in cam sleeve  350 , but clear the inside of housing  330 . Shaft  343  should have a clearance fit within the smallest diameter of bore  365  of hammer  360 . Head  344  is splined for a close, easily sliding fit in splined bore  365  of hammer  360 . Spring retention stub  345  should protrude from head  344  at least the diameter of the wire used for latch spring  303 , but should have positive clearance from latch spring guide  380  when latch  340  is at the top of its stroke. Cam pins  342  and the tops of splines  344  should be hardened or coated with a hard substance and polished for easy sliding and long wear life.  
         [0040]    Hammer  360  shown in side view in FIG. 11 and in top view in FIG. 11A should be made of similar material to punch head  310 , anvil  320 , and latch  340 . Hammer base  361  should have a close, easily sliding cylindrical fit in cam sleeve  350 , but with guide pins  362  evenly spaced around the perimeter (three shown but the actual number is not critical) which extend into guide slots  358  in cam sleeve  350  but clear the inside of housing  330 . Hammer  360  has a bore  365  at the center down its length to clear latch shaft  343  and internally splined for a close, easily sliding fit with the splines on head  344  of latch  340 . The base is counter-bored ( 363 ) from the bottom for a close, easily sliding cylindrical fit around the outer diameter of head  344  of latch  340  to allow the splines in hammer  360  to disengage the splines on the latch with head  344  of latch  340  still constrained within counter bore  363  of hammer  360 . Hammer body  364  should fit within hammer spring  301  and be as long as possible while leaving positive clearance between it and end cap  370  when hammer  360  is at the top of its stroke. Guide pins  362  and the bottoms of splines  365  should be hardened or coated with a hard substance and polished for easy sliding and long wear life.  
         [0041]    Cam sleeve  350  shown in FIG. 12 is a tube with guide slots  358  for hammer  360  at one end and cam slots  353  for the latch at the other end. Inside bore  351  of cam sleeve  350  should be accurately finished within a very close tolerance of its nominal diameter, straight and parallel to the outside of the sleeve. The hammer end of the sleeve should be chamfered  352  on the inside to prevent snagging of hammer spring  301  on the edge. Cam slots  353  rotate latch  340  at each end of its travel to align and unalign latch head splines  344  with hammer bore splines  365 . The bottoms of cam slots  357  set the initial rotation of latch  340  to positively misalign latch head splines  344  from hammer bore splines  365 . Upper ends  354  of the misalignment portions of the cam slots slope to upper travel limits  355  of cam slots  353 , which are oriented to rotate latch head splines  344  into alignment with hammer bore splines  365 . The bottoms of the alignment portions  356  of cam slots  353  slope back to the bottoms of the cam slots to rotate latch head splines  344  back out of alignment with hammer bore splines  365 . Guide slots  358  are straight slots that prevent rotation of hammer  360  and limit its downward travel. The entirety of cam sleeve  350  should be hardened or coated with a hard substance and polished for easy sliding and long wear life.  
         [0042]    Housing  330  shown in FIG. 13 has an inside bore  331  within which cam sleeve  350  should have a close, easily sliding cylindrical fit. Lip  332  at the bottom of the housing retains both cam sleeve  350  and anvil  320  but is bored  333  for protrusion of the shaft  322  of anvil  320  (FIG. 9). The outside of housing  334  is threaded  335  over part of its length for installation of end cap  370 . Threads  335  should extend over a long enough area to allow some adjustment of hammer spring  301  force by partially unthreading end cap  370 . Upper portion  336  of the outside of housing  330  should be relieved to slightly below the minor diameter of the threaded portion of housing  335  to provide clearance for the threads in end cap  372 . Groove  337  for cam sleeve retaining ring  302  should be positioned to allow cam sleeve retaining ring  302  to solidly locate cam sleeve  350  against lip  332  at the bottom of the housing.  
         [0043]    Latch spring guide  380  shown in FIG. 14 is, in a preferred embodiment, simply a cylindrical pin sized to fit inside the latch spring and including some provision  381  for attaching it to end cap  370 . While the drawing shows screw threads for attachment provision  381 , a simple press or shrink type interference fitting would work as well. Free end  382  of latch spring guide  380  should be chamfered or radiused to prevent snagging on latch spring  303 .  
         [0044]    End cap  370  shown in FIG. 15 has a section bored to clear threads  335  on housing  330  deep enough to cover housing threads  335  when end cap  370  is partially unscrewed for reduced hammer spring  301  tension. Adjacent to clearance bored section  371  is a section  372  threaded to match threaded section  335  of housing  330 . Adjacent to threaded section  372  of end cap  370  is a short section  373  bored to clear relieved upper section  336  of the housing and produce a shoulder  374  which provides a positive stop for threading end cap  370  onto the housing  330 . The profile of section  375  between shoulder  374  and hammer spring reaction surface  376  is not critical as long as it provides clearance for hammer spring  301  but the tapered section shown will ease assembly of the unit. The latch spring guide attachment provision  377  should match the attachment provision used on latch spring guide  381 .  
       PUNCH MECHANISM OPERATION  
       [0045]    FIGS.  16 - 19  show center punch  300  with portions of cam sleeve  350 , hammer  360 , and latch  340  cut away in four different phases of the center punch  300 &#39;s operating sequence. Latch spring  303  and latch spring guide  380 , although shown in FIG. 7, are omitted from FIGS.  17 - 19  for clarity.  
         [0046]    In FIG. 16, point  311  of center punch  300  is resting against the work with little or no pressure applied. Hammer spring  301  extends hammer  360  in the direction of point  311 . Hammer  360  is restrained from moving towards point  311  by hammer guide pins  362 , which are at the bottoms of guide slots  358 . Latch spring  303  holds latch  340  at the bottom of its stroke against the anvil  320  and holds punch housing  330  and end cap  370  at their fully extended positions.  
         [0047]    [0047]FIG. 16A is an enlarged top view of hammer  360  and latch  340 , which shows their relative rotational positions in the phase of center punch  300 &#39;s operation that is depicted in FIG. 16. The portions of the splines on latch head  344  depicted with dashed lines are hidden from view due to their misalignment from the splines in hammer bore  365 .  
         [0048]    As the user operates the punch by pressing punch housing  330  and end cap  370  toward the work piece, hammer spring  301  pushes hammer  360  toward latch  340  until the ends of the splines in hammer bore  365  meet the splines on latch head  344 . From that point, further depression of the punch body compresses hammer spring  301  between hammer  360  and end cap  370  until the tops of cam slots  353  reach cam pins  342  on latch  340 .  
         [0049]    The point where the tops of cam slots  353  have reached cam pins  342  on latch  340  is depicted in FIG. 17. At this point, the relative rotational positions of hammer  360  and latch  340  are still as shown in FIG. 16A. However, since the tops of cam slots  353  in cam sleeve  350  are angled, further depression of the punch body causes the angled portions of cam slots  353  to apply a side force to cam pins  342  on latch  340  which, because latch  340  is confined within cam sleeve  350 , causes latch  340  to rotate. When the peaks of cam slots  353  have reached latch cam pins  342 , as shown in FIG. 18, latch  340  has rotated enough to align the splines on latch head  344  with the splines in hammer bore  365  as shown in FIG. 18A. At this point, hammer  360  becomes free to slide around latch head  344  and the energy stored in hammer spring  301  when it was compressed forces hammer  360  toward latch  340 . The base of hammer  360  impacts the base of latch  340  which, being in direct contact with the anvil, transfers the energy of the impact to anvil  320  which transfers it to punch  310 , driving the point of punch head  310  into the work piece.  
         [0050]    As the user releases pressure on end cap  370  and housing  330 , latch spring  303  pushes end cap  370 , housing  330  and cam sleeve  350  away from the work. At the point shown in FIG. 19, the splines on latch head  344  clear the splines in hammer bore  365  and the bottoms of cam slots  353  begin to apply a side force on latch cam pins  342  opposite to the side force applied when the punch body was pressed toward the work piece. This opposite side force rotates latch  340  back to its original position resetting the center punch for its next use.  
         [0051]    Although the preceding description of the operation of the center punch refers to the rotation of the latch  340 , cam sleeve  350  does not have to be (and, in the embodiment described, is not) restrained from rotating. Thus, depending on relative friction between parts, cam sleeve  350  and hammer  360  could rotate instead of, or in addition to, latch  340 . The important motion in the operation of the center punch is the rotation of the latch relative to the hammer. Other possible designs could use a guide slot for latch  350  and a cam slot to rotate hammer  360  or cam slots to rotate both latch  340  and hammer  360  in opposite directions.  
         [0052]    The present invention provides a number of advantages over the prior art. When compared to the use of an alignment fixture, optical alignment sight and basic center punch with manually wielded hammer of prior art FIG. 2, the constrained motion of the hammer in the preferred embodiment of the present invention described herein provides a consistent impact orientation that is difficult to achieve by hand. While the maximum achievable accuracy is no better, the range of error is much smaller.  
         [0053]    The slide hammer punch in prior art FIGS. 3A and 3B can be made to similar tolerances as the present invention for accuracy, but the present invention provides the ability to work on non horizontal surfaces as shown in FIGS. 23 and 24.  
         [0054]    The rocking motion of the mechanism in the prior art center punch shown in FIGS. 4A through 4C requires much more clearance than the rotating mechanism of this invention and, therefore, cannot achieve the same level of consistency.  
         [0055]    The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.