Abstract:
A mechanical pencil assembly including an eraser detachably secured to the writing end thereof, said eraser defining a bore therethrough, diameter of said bore larger than the diameter of the writing tip of said mechanical pencil such that said writing tip can be projected therethrough when writing is desired and retracted therefrom when erasure is desired. The need for a user to adjust his or her grip of the mechanical pencil assembly to transition from writing to erasure or from erasure to writing is completely eliminated, making both transitions nearly immediate and nearly effortless. A further feature of the present invention is a first storage compartment disposed within said barrel wherein additional pencil leads can be stored and a second storage compartment disposed within said barrel wherein additional erasers can be stored.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to a mechanical pencil assembly including an eraser detachably secured to the writing end thereof, said eraser defining a bore therethrough, diameter of said bore larger than the diameter of the writing tip of said mechanical pencil assembly such that said writing tip can be projected therethrough when writing is desired and retracted therefrom when erasure is desired. A further feature of the present invention is a first storage compartment within said pencil wherein additional pencil leads can be stored and a second storage compartment within said pencil wherein additional erasers can be stored. 
   When writing, drawing, or otherwise using a writing utensil to mark upon a surface, hereafter called writing, erroneous marks can occur. It has become common practice to secure an eraser to the end of a writing utensil opposite the writing end, hereafter called the non-writing end, that can be readily used for erasure. However, to use said eraser, said writing utensil must be turned around to position said eraser at the writing surface, which is a great inconvenience. 
   Several devices has been proposed to permit erasure via an eraser secured to a writing utensil without requiring said writing utensil to be turned around. One solution is to statically secure an eraser near the writing tip of a writing utensil such that erasure can be accomplished by slightly moving said writing utensil to position said statically secured eraser near the writing surface. 
   U.S. Pat. No. 6,732,407 (Weiss) discloses a writing implement, which generally comprises a forward-positioned eraser that circumscribes the shaft of the writing implement and that may have an annular or doughnut shape. 
   U.S. Pat. No. 5,555,602 (Leamond) discloses an eraser device, which generally comprises an elongated cylindrical finger grip section with an internal bore defined therethrough, an internal conical bore section that is aligned with the internal bore so that the device can be slid or fitted onto the writing end of a writing instrument, and at least one eraser arm that extends radially outward from the finger grip section, is angled forward towards the front end of the device, and is configured with an eraser such that an operator can use the eraser by merely tilting and rotating the finger grip section to bring the eraser arm and eraser into contact with a writing surface. 
   U.S. Pat. No. 4,899,419 (Saleen) discloses a pencil eraser assembly having an elongated hollow eraser sleeve formed to align in elemental parallel spaced relationship with both the frustum shaped segment and the portion of the cylindrical barrel segment of a pencil, in which the sleeve has an opening adjacent to the end point of the frustum segment for holding an elongated eraser plug within the sleeve and adjacent to the pencil lead of the pencil. 
   Some disadvantages of the preceding devices are that they can be ineffective, obstruct the writing surface, or otherwise obstruct normal writing procedures. Another solution to permit erasure via an eraser secured to a writing utensil without requiring said writing utensil to be turned around is to secure a projectable and retractable eraser on the writing end of said writing utensil such that said eraser can be projected when erasure is desired and retracted when writing is desired. 
   U.S. Pat. No. 2,815,002 (Mayes) discloses an eraser for mechanical pencils, which generally comprises an eraser that is provided with a centrally disposed longitudinally positioned opening through which the lead extends and which is positioned at the base of the conical-shaped section of the point of the pencil and is slidably mounted and adapted to be actuated by a button on the surface of a barrel of the pencil wherein, should it be desired to make an erasure, the eraser is actuated by the button to slide outwardly beyond the point of the lead with the surrounding conical-shaped portion of the pencil expanding, whereby an erasure may be made and, after completing the erasure, the eraser is adapted to be retracted by the button and the point adapted to be used for writing. 
   U.S. Pat. No. 2,069,462 (Rouse) discloses a eraser that can be readily projected or extended to cover the writing point of a pencil so that an erasure can be made with the same end of the pencil as is used for writing, which generally comprises a tubular eraser attached to a member that is allowed to slide freely on the tube of a mechanical pencil by means of a force applied by one of the fingers and a spring that provides a restoring force to retract the member when released by the finger used to extend the member. 
   U.S. Pat. No. 1,580,183 (Veillette) discloses a writing implement with the eraser on the same end as the writing point, which generally comprises an eraser adapted to slidably telescope the writing point by means of a slight movement by one of the fingers during writing and which may then be pulled back by a similar movement of the finger. 
   U.S. Pat. No. 1,473,090 (Ferry) discloses an attachment for lead pencils that is disposed adjacently to the sharpened end of a pencil where it will not inconvenience the writer, which generally comprises a clasp and an erasing block and may have a sliding movement to dispose the attachment at or below the sharpened end of the pencil for erasing. 
   A disadvantage of the directly preceding devices is that they can be inconvenient to use since either a constant force must be applied by a writing finger to project and keep projected the eraser, a constant force must be applied by a writing finger retract the eraser which causes that writing finger to come to rest at a position not ideal for writing, or both. Another solution to permit erasure via an eraser secured to a writing utensil without requiring said writing utensil to be turned around is to secure an eraser on the writing end of said writing utensil and permit the writing tip to be projected when writing is desired and retracted when erasure is desired. 
   U.S. Pat. No. 5,127,130 (Copito) discloses a pencil eraser or erasable ink ball point pen eraser in the shape and form of a cowling sleeve affixed to the front end of either a double-acting mechanical pencil or single-acting ball point pen, wherein the writing elements of the pencil or pen may be withdrawn through spring action, making the eraser available for almost immediate application at the writing end of either instrument to erase whatever writing is to be erased. 
   Because the directly preceding device makes use of a double-acting mechanical pencil or a single-acting ball point pen, it lacks an effective and convenient means to both project and retract the writing tip and, as it relates to a mechanical pencil, lacks an effective and convenient means to advance a pencil lead forward through the writing tip. Accordingly, what is desired, and not heretofore been developed, is a writing utensil assembly wherein the transition from writing to erasure and from erasure to writing is nearly immediate and nearly effortless. Furthermore, what is desired, and not heretofore been developed, is a writing utensil assembly that includes an eraser secured to the front end thereof and a writing tip that is projectable and retractable wherein the writing fingers rest in the writing position after they are used to project the writing tip towards the writing surface, the writing fingers rest in the erasure position after they are used to retract the writing tip away from the writing surface, and as it relates to mechanical pencils, the desired writing finger permanently rests on or conveniently near a lead-advancing knock member. 
   BRIEF SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a mechanical pencil assembly wherein the transition from writing to erasure and from erasure to writing is nearly immediate and nearly effortless. 
   It is an object of the present invention to provide a mechanical pencil assembly including a tubular eraser detachably secured to the writing end thereof through which the writing tip can be projected when writing is desired and retracted when erasure is desired. 
   It is object of the present invention to provide a means of projecting the writing tip from the retracted position for erasure to the projected position for writing. 
   It is object of the present invention to provide a means of projecting the writing tip from the retracted position for erasure to the projected position for writing such that the writing fingers rest in the writing position thereafter. 
   It is object of the present invention to provide a means of retracting the writing tip from the projected position for writing to the retracted position for erasure. 
   It is object of the present invention to provide a means of retracting the writing tip from the projected position for writing to the retracted position for erasure such that the writing fingers rest in the erasure position thereafter. 
   It is object of the present invention to provide a means of advancing a pencil lead forward through the writing tip. 
   It is object of the present invention to provide a means of advancing a pencil lead forward through the writing tip such that the desired writing finger permanently rests on or conveniently near the lead-advancing knock member. 
   It is object of the present invention to provide a means of locking the writing tip in the projected position for writing. 
   It is object of the present invention to provide a means for storage of additional pencil leads within the mechanical pencil assembly. 
   It is object of the present invention to provide a means for storage of additional tubular erasers within the mechanical pencil assembly. 
   It is object of the present invention to provide a mechanical pencil assembly that is inexpensive to manufacture. 
   It is object of the present invention to provide a mechanical pencil assembly that is easy to use. 
   It is object of the present invention to provide a mechanical pencil assembly that is esthetically pleasing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of the parts comprising the mechanical pencil assembly of the preferred embodiment of the present invention. 
       FIG. 2  is a front elevation view of the mechanical pencil assembly shown in  FIG. 1  fully assembled. 
       FIG. 3   a  is a cross-sectional view of the mechanical pencil assembly shown in  FIG. 2  taken along the line A—A when the writing elements are projected for writing,  FIG. 3   b  is a cross-sectional view of the mechanical pencil assembly shown in  FIG. 2  taken along the line A—A when the knock member is pressed to advance a piece of lead, and  FIG. 3   c  is a cross-sectional view of the mechanical pencil assembly shown in  FIG. 2  taken along the line A—A when the writing elements are retracted for erasure. 
       FIG. 4   a  is a cross-sectional view of the mechanical pencil assembly shown in  FIG. 2  taken along the line B—B when the writing elements are projected for writing,  FIG. 4   b  is a cross-sectional view of the mechanical pencil assembly shown in  FIG. 2  taken along the line B—B when the knock member is pressed to advance a piece of lead, and  FIG. 4   c  is a cross-sectional view of the mechanical pencil assembly shown in  FIG. 2  taken along the line B—B when the writing elements are retracted for erasure. 
       FIG. 5   a  is a perspective view from above of the rear barrel,  FIG. 5   b  is a perspective view from below of the rear barrel,  FIG. 5   c  is a side elevation view of the rear barrel, and  FIG. 5   d  is a front elevation view of the rear barrel. 
       FIG. 6   a  is a perspective view from above of the front barrel,  FIG. 6   b  is a perspective view from below of the front barrel,  FIG. 6   c  is a side elevation view of the front barrel,  FIG. 6   d  is a front elevation view of the front barrel, and  FIG. 6   e  is a top elevation view of the front barrel. 
       FIG. 7   a  is a perspective view from above of the first slide member,  FIG. 7   b  is a perspective view from below of the first slide member,  FIG. 7   c  is a side elevation view of the first slide member,  FIG. 7   d  is a front elevation view of the first slide member, and  FIG. 7   e  is a top elevation view of the first slide member. 
       FIG. 8   a  is a perspective view from above of the second slide member,  FIG. 8   b  is a perspective view from below of the second slide member,  FIG. 8   c  is a side elevation view of the second slide member,  FIG. 8   d  is a front elevation view of the second slide member, and  FIG. 8   e  is a top elevation view of the second slide member. 
       FIG. 9   a  is a perspective view from above of the chuck guide,  FIG. 9   b  is a perspective view from below of the chuck guide,  FIG. 9   c  is a side elevation view of the chuck guide,  FIG. 9   d  is a front elevation view of the chuck guide, and  FIG. 9   e  is a top elevation view of the chuck guide. 
       FIG. 10   a  is a perspective view from above of the assembly comprising the first slide member and chuck guide adjacent to the arm lock elements of the front barrel (front barrel not shown),  FIG. 10   b  is a perspective view from below of the said assembly adjacent to the arm lock elements,  FIG. 10   c  is a side elevation view of the said assembly adjacent to the arm lock elements,  FIG. 10   d  is a front elevation view of the said assembly adjacent to the arm lock elements, and  FIG. 10   e  is a top elevation view of the said assembly adjacent to the arm lock elements. 
       FIG. 11   a  is a perspective view from above of the lead guide tube,  FIG. 11   b  is a perspective view from below of the lead guide tube,  FIG. 11   c  is a side elevation view of the lead guide tube,  FIG. 11   d  is a front elevation view of the lead guide tube, and  FIG. 11   e  is a top elevation view of the lead guide tube. 
       FIG. 12   a  is a perspective view from above of the chuck,  FIG. 12   b  is a perspective view from below of the chuck,  FIG. 12   c  is a side elevation view of the chuck, and  FIG. 12   d  is a front elevation view of the chuck. 
       FIG. 13   a  is a perspective view from above of the funnel-shaped member,  FIG. 13   b  is a perspective view from below of the funnel-shaped member,  FIG. 13   c  is a side elevation view of the funnel-shaped member, and  FIG. 13   d  is a front elevation view of the funnel-shaped member. 
       FIG. 14   a  is a perspective view from above of the assembly comprising the second slide member, lead guide tube, funnel-shaped member, and chuck,  FIG. 14   b  is a perspective view from below of the said assembly,  FIG. 14   c  is a side elevation view of the said assembly,  FIG. 14   d  is a front elevation view of the said assembly, and  FIG. 14   e  is a top elevation view of the said assembly. 
       FIG. 15   a  is a perspective view from above of the assembly comprising the second slide member, lead guide, funnel-shaped member, and chuck disposed on the assembly comprising the first slide member and chuck guide adjacent to the arm lock elements of the front barrel (front barrel not shown),  FIG. 15   b  is a perspective view from below of the said assemblies adjacent to the arm lock elements,  FIG. 15   c  is a side elevation view of the said assemblies adjacent to the arm lock elements,  FIG. 15   d  is a front elevation view of the said assemblies adjacent to the arm lock elements, and  FIG. 15   e  is a top elevation view of the said assemblies adjacent to the arm lock elements. 
       FIG. 16   a  is a perspective view from above of the rear flange,  FIG. 16   b  is a perspective view from below of the rear flange,  FIG. 16   c  is a side elevation view of the rear flange,  FIG. 16   d  is a front elevation view of the rear flange, and  FIG. 16   e  is a top elevation view of the rear flange. 
       FIG. 17   a  is a perspective view from above of the front flange,  FIG. 17   b  is a perspective view from below of the front flange,  FIG. 17   c  is a side elevation view of the front flange, and  FIG. 17   d  is a front elevation view of the front flange. 
       FIG. 18   a  is a perspective view from above of the eraser cup,  FIG. 18   b  is a perspective view from below of the eraser cup,  FIG. 18   c  is a side elevation view of the eraser cup,  FIG. 18   d  is a front elevation view of the eraser cup, and  FIG. 18   e  is a top elevation view of the eraser cup. 
       FIG. 19   a  is a perspective view from above of the tubular eraser,  FIG. 19   b  is a perspective view from below of the tubular eraser,  FIG. 19   c  is a side elevation view of the tubular eraser, and  FIG. 19   d  is a front elevation view of the tubular eraser. 
       FIG. 20   a  is a perspective view from above of the tip,  FIG. 20   b  is a perspective view from below of the tip,  FIG. 20   c  is a side elevation view of the tip, and  FIG. 20   d  is a front elevation view of the tip. 
       FIG. 21   a  is a perspective view from above of the lead storage tank,  FIG. 21   b  is a perspective view from below of the lead storage tank,  FIG. 21   c  is a side elevation view of the lead storage tank, and  FIG. 21   d  is a front elevation view of the lead storage tank. 
       FIG. 22   a  is a perspective view from above of the tank cap,  FIG. 22   b  is a perspective view from below of the tank cap,  FIG. 22   c  is a side elevation view of the tank cap, and  FIG. 22   d  is a front elevation view of the tank cap. 
       FIG. 23   a  is a perspective view from above of the knock member,  FIG. 23   b  is a perspective view from below of the knock member,  FIG. 23   c  is a side elevation view of the knock member,  FIG. 23   d  is a front elevation view of the knock member, and  FIG. 23   e  is a top elevation view of the knock member. 
       FIG. 24   a  is a perspective view from above of the spring and  FIG. 24   b  is a perspective view from below of the spring. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a perspective view of each part of the mechanical pencil assembly  17  of the present invention, generally comprising a front barrel  5  and a rear barrel  6 , in which is disposed a first slide member  10 , a second slide member  11 , a spring  12 , a lead guide tube  9 , a funnel-shaped member  901 , a chuck  13 , a chuck guide  14 , a tip  15 , a lead storage tank  7 , and a tank cap  701 . On the front end of the front barrel  5  is secured a front flange  3 , an eraser cup  2 , and a tubular eraser  1 , and within a side of the front barrel  5  is secured a knock member  8 . On the rear end of the rear barrel  6  is secured a rear flange  4 , an eraser cup  2 , and a tubular eraser  1 . The lead storage tank  7  stores additional pencil leads  16  and the rear barrel  6  stores additional tubular erasers  1 . 
     FIG. 2  shows a front elevation view mechanical pencil assembly  17  shown  FIG. 1  fully assembled. During writing or erasure the user holds the mechanical pencil assembly  17  in the same manner, with the index finger resting on or near the knob  1001  to project the writing elements of the mechanical pencil assembly  17  for writing, with the thumb resting on or near one of the retraction buttons  502  and the middle finger resting on or near the other retraction button  502  to retract the writing elements for erasure, and with the thumb resting on or near the knock member  8  to advance a pencil lead  16 , such that the transition from writing, when the writing elements are projected and a pencil lead  16  is extended thereout, to erasure, when the writing elements are retracted, as well as the transition from erasure to writing, is accomplished simply by applying force with the appropriate finger or fingers. 
   Hereafter the term writing elements is used to describe the assembly comprising the first slide member  10 , chuck guide  14 , second slide member  11  lead guide tube  9 , funnel-shaped member  901 , chuck  13 , tip  15 , and pencil lead  16 . Hereafter the term projected is used to describe the position of the writing elements of the mechanical pencil assembly  17  at a forward position such that the front-most point of the tip  15  is disposed in front of the front-most point of the tubular eraser  1  secured to the front end of the front barrel  5  and a pencil lead  16  is extended thereout a distance suitable for writing to permit writing. Hereafter the term retracted is used to describe the state of the writing elements of the mechanical pencil assembly  17  at a rearward position such that the front-most point of a pencil lead  16  extending out from the tip  15  a distance suitable for writing is disposed behind the front-most point of the eraser cup  2  secured to the front end of the front barrel  5  to permit erasure. 
     FIG. 3   a  shows a cross-sectional view of the mechanical pencil assembly  17  shown in  FIG. 2  taken along the line A—A when the writing elements of the mechanical pencil assembly  17  are projected. The front barrel  5  and rear barrel  6  are joined to comprise the generally cylindrical barrel of the mechanical pencil assembly  17 . On the front end of the front barrel  5  is secured a front flange  3 , within which are detachably secured an eraser cup  2  and a tubular eraser  1 . On the rear end of the rear barrel  6  is secured a rear flange  4 , within which are detachably secured an eraser cup  2  and a tubular eraser  1 . 
   An assembly comprising a lead storage tank  7  and a tank cap  701  is axially secured within the rear barrel  6  for storage of additional pencil leads  16  therein. Additional pencil leads  16  are placed therein or removed therefrom by removing the tubular eraser  1  and eraser cup  2  detachably secured to the rear end of the rear barrel  6  and removing the tank cap  701  detachably secured to the lead storage tank  7 . 
   The outer diameter of the assembly comprising the lead storage tank  7  and tank cap  701  is smaller than the bore defined through the tubular eraser  1  and the inner diameter of the rear barrel  6  is larger than the outer diameter of the tubular eraser  1  to permit additional tubular erasers  1  to be stored axially within the rear barrel  6 . Additional tubular erasers  1  are placed therein or removed therefrom by removing the tubular eraser  1  and eraser cup  2  detachably secured to the rear of the rear barrel  6 . 
   The lead guide tube  9  with a funnel-shaped member  901  secured at the rear end thereto and a chuck  13  secured at the front end thereto is secured to the second slide member  11  via the projecting members  902 . The chuck  13  is axially disposed within the chuck guide  14  secured to the first slide member  10 . A tip  15  is detachably secured to the front end of the chuck guide  14  to guide a pencil lead  16  out from the front end of the mechanical pencil assembly  17  upon actuation of the knock member  8  disposed within the knock member opening  504  defined within a side of the front barrel  5 . 
   A spring  12  is axially disposed within the front barrel  5  and about the chuck guide  14  and tip  15  to bias the writing elements rearward. The second slide member  11  is disposed in the channel  1004  defined on the first slide member  10 . Rearward motion of the second slide member  11  is prevented by the stop element  1003  defined on the first slide member  10 , and rearward motion of the first slide member  10  is prevented by two arm lock elements  505  (not shown) defined within the front barrel  5 . 
     FIG. 3   b  shows a cross-sectional view of the mechanical pencil assembly  17  shown in  FIG. 2  taken along the line A—A when the knock member  8  is pressed to advance a pencil lead  16 . Actuation of the knock member  8  moves the second slide member  11 , lead guide tube  9 , funnel-shaped member  901 , chuck  13 , and pencil lead  16  forward against the rearward bias force of the spring  12 . Forward motion of the first slide member  10 , chuck guide  14 , and tip  15  is prevented by the stop element  506  defined within the front barrel  5 . 
   Releasing the knock member  8  returns the second slide member  11 , lead guide tube  9 , funnel-shaped member  901 , and chuck  13  to the positions shown in  FIG. 3   a.    
     FIG. 3   c  shows a cross-sectional view of the mechanical pencil assembly  17  shown in  FIG. 2  taken along the line A—A after the retraction buttons  502  (not shown) are pressed to retract the writing elements. Actuation of the retraction buttons  502  (not shown) causes the first slide member  10 , chuck guide  14 , tip  15 , second slide member  11 , lead guide tube  9 , funnel-shaped member  901 , chuck  13 , and pencil lead  16  to move rearward with the rearward bias force of the spring  12  until the first slide member  10  contacts the stop element  601  defined on the rear barrel  6 . 
   To return the writing elements to the projected position shown in  FIG. 3   a  a forward force is applied to the knob  1001  defined on the first slide member  10  and disposed within the slider access opening  503  defined within a side of the front barrel  5  by a finger of the user. 
     FIG. 4   a  shows a cross-sectional view of the mechanical pencil assembly  17  shown in  FIG. 2  taken along the line B—B when the writing elements are projected. The front barrel  5  defines two retraction buttons  502  adjacent to the arms  1002  defined on the first slide member  10 . Rearward motion of the writing elements is prevented by an arm lock element  505  (not shown) disposed behind each arm  1002 . 
     FIG. 4   b  shows a cross-sectional view of the mechanical pencil assembly  17  shown in  FIG. 2  taken along the line B—B when the knock member  8  is pressed to advance a pencil lead  16 . 
     FIG. 4   c  shows a cross-sectional view of the mechanical pencil assembly  17  shown in  FIG. 2  taken along the line B—B after the retraction buttons  502  are pressed to retract the writing elements. Actuation of the retraction buttons  502  displaces the arms  1002  laterally away from the adjacent arm lock elements  505  (not shown), permitting substantially unimpeded rearward motion of the writing elements until the first slide member  10  contacts the stop element  601 . 
     FIG. 5   a  through  FIG. 5   d  show four views of the rear barrel  6  and the stop element  601  defined thereon for preventing rearward motion of the writing elements therebeyond. 
     FIG. 6   a  through  FIG. 6   e  show five views of the front barrel  5 . A front bore  501  is defined at the front end therethrough to permit substantially unimpeded projection and retraction of the tip  15  therethrough. The diameter of the front bore  501  is only slightly larger than the outer diameter of the tip  15  to provide lateral stability of the writing elements when writing. A knock member opening  504  is defined within a side of the front barrel  5  to permit the knock member  8  to communicate with the second slide member  11  to advance a pencil lead  16 . A slider access opening  503  is defined within an opposite side of the front barrel  5  to permit a user to communicate with the first slide member  10  by contacting the first slide member  10  with a finger to project the writing elements. Two arm lock elements  505  are defined within the front barrel  5 , each disposed behind an arm  1002  when the writing elements are projected in the assembled mechanical pencil assembly  17  to prevent rearward motion of the writing elements. Two retraction buttons  502  are defined on the front barrel  5 , each adjacent to an arm  1002  in the assembled mechanical pencil assembly  17 , such that pressing the retraction buttons  502  displaces each arm  1002  laterally away from the adjacent arm lock element  505  to permit retraction of the writing elements. A stop element  506  is defined within the front barrel  5  at a front end therewithin to prevent forward motion of the first slide member  10  therebeyond. 
     FIG. 7   a  through  FIG. 7   e  show five views of the first slide member  10 . A knob  1001  is defined on the underside thereof, which is disposed within the knock member opening  504  of the front barrel  5  in the assembled mechanical pencil assembly  17  to permit a user to contact the first slide member  10  with a finger and apply a forward force to project the writing elements. Two arms  1002  are defined on opposite sides of the first slide member  10  to prevent rearward motion of the writing elements when projected in the assembled mechanical pencil assembly  17 . In the preferred embodiment of the present invention each arm  1002  is formed of a flexible material, such as plastic, that permits bending when force is applied thereto. When the writing elements are projected in the assembled mechanical pencil assembly  17  the arms  1002  are disposed in front of the arm lock elements  505  and adjacent to the retraction buttons  502 , such that when the retraction buttons  502  are pressed, the arms  1002  are displaced laterally away from the arm lock elements  505  to permit rearward motion of the writing elements. A channel  1004  oriented along the axis of the mechanical pencil assembly  17  is defined on the first slide member  10 , in which the second slide member  11  is disposed in the assembled mechanical pencil assembly  17 . A stop element  1003  is defined at a rear end of the channel  1004  to prevent rearward motion of the second slide member  11  therebeyond. The stop element  1003  also functions as the point of securement of the chuck guide  14  to the first slide member  10 . 
     FIG. 8   a  through  FIG. 8   e  show five views of the second slide member  11  and the two projecting members  1101  defined thereon. The projecting members  1101  function as the point of securement of the lead guide tube  9  to the second slide member  11 . The shape of the underside of the second slide member  11  is complimentary to the shape of the channel  1004  defined on the first slide member  10  to permit substantially unimpeded motion of the second slide member  11  thereon upon actuation of the knock member  8 . 
     FIG. 9   a  through  FIG. 9   e  show five views of the chuck guide  14  and the chuck guide opening  1401  defined thereon. The inner diameter of the chuck guide  14  is larger than the outer diameter of the lead guide tube  9  to permit the lead guide tube  9  to be disposed therein and to permit substantially unimpeded axial motion therein. The chuck guide opening  1401  provides an opening adjacent to the projecting members  902  defined on the lead guide tube  9  to permit the projecting members  902  to contact the projecting members  1101  defined on the second slide member  11  for securement of the lead guide tube  9  to the second slide member  11 . 
     FIG. 10   a  through  FIG. 10   e  show five views of the assembly comprising the first slide member  10  and chuck guide  14  in the projected position wherein the arms  1002  are disposed in front of the arm lock elements  505  (front barrel  5  not shown). 
     FIG. 11   a  through  FIG. 11   e  show five views of the lead guide tube  9  and the projecting member  902  that secures the lead guide tube  9  to the second slide member  11  in the assembled mechanical pencil assembly  17 . 
     FIG. 12   a  through  FIG. 12   d  show four views of the chuck  13 . In the assembled mechanical pencil assembly  17  the chuck  13  is secured to the front end of the lead guide tube  9  and is disposed axially within the chuck guide  14 . 
     FIG. 13   a  through  FIG. 13   d  show four views of the funnel-shaped member  901 . In the assembled mechanical pencil assembly  17  the funnel-shaped member  901  is secured to the rear end of the lead guide tube  9  and is disposed axially within the lead storage tank  7  to guide a pencil lead  16  from the lead storage tank  7  to the lead guide tube  9 . The outer diameter of the funnel-shaped member  901  is slightly smaller than the inner diameter of the lead storage tank  7 . 
     FIG. 14   a  through  FIG. 14   e  show five views of the assembly comprising the second slide member  11 , lead guide tube  9 , funnel-shaped member  901 , and chuck  13 . 
     FIG. 15   a  through  FIG. 15   e  show five views of the assembly comprising the second slide member  11 , lead guide tube  9 , funnel-shaped member  901 , and chuck  13  disposed on the assembly comprising the first slide member  10  and chuck guide  14 , wherein the second slide member  11  is disposed in the channel  1004  defined on the first slide member  10  and both assemblies are in the projected positions wherein the arms  1002  defined on the first slide member  10  are disposed in front of the arm lock elements  505  (front barrel  5  not shown). 
     FIG. 16   a  through  FIG. 16   e  show five views of the rear flange  4  that secures an eraser cup  2  to the rear end of the rear barrel  6  in the assembled mechanical pencil assembly  17 . 
     FIG. 17   a  through  FIG. 17   d  show four views of the front flange  3  that secures an eraser cup  2  to the front end of the front barrel  5  in the assembled mechanical pencil assembly  17 . 
     FIG. 18   a  through  FIG. 18   e  show five views of the eraser cup  2  that can secure a tubular eraser  1  to the rear end of the rear barrel  6  or to the front end of the front barrel  5 . The diameter of the eraser cup bore  201  defined therethrough is larger than the outer diameter of the tip  15  to permit projection and retraction of the tip  15  therethrough and is larger than the outer diameter of the assembly comprising the lead storage tank  7  and tank cap  701  to permit the said assembly to be disposed therein to provide lateral stability of the said assembly. Identical eraser cups  2  can be used to secure a tubular eraser  1  to the front end of the front barrel  5  and to secure a tubular eraser  1  to the rear end of the rear barrel  6 , which helps keep manufacturing costs low. 
     FIG. 19   a  through  FIG. 19   d  show four views of the tubular eraser  1  that can be secured to the front end of the front barrel  5  and to the rear end of the rear barrel  6 . The diameter of the tubular eraser bore  101  defined therethrough is larger than the outer diameter of the tip  15  to permit projection and retraction of the tip  15  therethrough. The diameter of the tubular eraser bore  101  is also larger than the outer diameter of the assembly comprising the lead storage tank  7  and tank cap  701  and the outer diameter of the tubular eraser  1  is smaller than the inner diameter of the rear barrel  6  to permit additional tubular erasers  1  to be stored within the rear barrel  6  about the lead storage tank  7 . Identical tubular erasers  1  can be used at both the front and rear ends of the mechanical pencil assembly  17 , which helps keep manufacturing costs low. 
     FIG. 20   a  through  FIG. 20   d  show four views of the tip  15  that guides a pencil lead  16  out from the front end of the mechanical pencil assembly  17 . In the assembled mechanical pencil assembly  17  the tip  15  is detachably secured to the front end of the chuck guide  14 . 
     FIG. 21   a  through  FIG. 21   d  show four views of the lead storage tank  7  that stores additional pencil leads  16 . In the assembled mechanical pencil assembly  17  the stop element  601  defined in the rear barrel  6  also functions to secure the lead storage tank  7  axially within the rear barrel  6 . 
     FIG. 22   a  through  FIG. 22   d  show four views of the tank cap  701 . In the assembled mechanical pencil assembly  17  the tank cap  701  is detachably secured to the rear end of the lead storage tank  7 . 
     FIG. 23   a  through  FIG. 23   e  show five views of the knock member  8 . In the assembled mechanical pencil assembly  17  the knock member  8  is secured within a side of the front barrel  5  adjacent to the second slide member  11 . 
     FIG. 24   a  through  FIG. 24   b  show two views of the spring  12  that is provides a rearward bias force to the writing elements. In the assembled mechanical pencil assembly  17  the front end of the spring  12  contacts the stop element  506  defined within the front barrel  5  and the rear end of the spring  12  contacts the second slide member  11 . 
   Although a specific embodiment of the present invention has been illustrated and described, many variations or modifications would be apparent that do not depart from the spirit and scope of the present invention, which are defined by the appended claims.