Abstract:
A drawing compass with a structure of L shape and a method of using the same provide improved single-hand manipulation and handling of drawing an arc or circle. The drawing compass comprises a handle rotatably mounted on one end of an arm and a pivot pin holder slidably mounted along the arm. One can make an arc or circle by simply holding the handle perpendicular to a drawing surface, placing the pivot pin at the center and making a circular motion guided by the arm of the compass. In the drawing process, the pressure applied on the marking point is directly controlled by hand. The compass is easy to use, inexpensive, and simple to manufacture.

Description:
BACKGROUND OF INVENTION 
   This invention relates to a drawing compass, and more specifically to a novel compass apparatus and the method of using the same. 
   Drawing compasses are well known as instruments for marking circles or arcs on draft paper or other surfaces. A traditional compass usually comprises of a handle and two legs with their upper ends pivotally attached to the handle. The free end of the first leg may be a pin or stylus. 
   The free end of the second leg may be a marking instrument such as a pencil, pen or chalk. The free ends of the legs can be moved open or close so that the distance between the pin and the tip of the marking instrument can be adjusted to a desired radius of a circle or arc. The compass is used by placing the pin of the first leg at the center, placing the marking tip at a start point of the circle or arc to be drawn, and twisting the handle to rotate the second leg around the first one with the marking tip scribing on the drawing surface. 
   Although traditional compasses have been used for many years, they have intrinsic deficiencies in usage. It requires a delicate control and balance of pressure applied on the two legs to keep one leg anchored at the center and the other rotating and scribing on the drawing surface while twisting and rotating the handle. It is difficult, as the compass is rotated by hand, to maintain the delicate pressure balance. When the pressure on marking tip becomes too light, the scribed line may be indistinct. When the pressure becomes too heavy, the friction may hinder the marking tip from scribing and even cause the pivot pin to lose anchor on the drawing surface. The manipulation requires practice and is a challenge for student, occasional users or persons with limited dexterity. 
   Beam compasses are also known, in which a pivot pin holder and a marking instrument holder are moveably mounted along a rigid intermediate beam. The manipulation of beam compasses requires both hands, one to hold the pivot pin in the center and the other to rotate the marking instrument around the pivotal pin. This type of compasses is generally designed for certain specific purposes and not for general usage. 
   There is a need for a novel type of drawing compass with easy usage and manipulation. 
   SUMMARY OF INVENTION 
   The present invention provides a novel drawing compass with features of easy usage and improved manipulation. The present invention further provides a method of using the same. And the drawing process can be easily accomplished with single hand. The drawing compass of the present invention comprises a horizontal arm, an elongated handle rotatably mounted on one end of the arm, a marking instrument attached on the lower end of the handle, and a pivot pin holder slidably mounted on the horizontal arm. Since the handle is mounted near its lower end to the horizontal arm, the structure, with the long vertically mounted handle on the left and the horizontal arm on the right, looks like a capital letter L. The unique shape and design of the present invention provide a novel and simple manipulation for drawing a circle or arc by one hand. The process of drawing a circle is as follows: hold the handle upright, place the pin point at the center and scribe a circle or arc as the circular motion is guided by the drawing compass with desired radius. While the circle or arc is been scribed, the pressure applied on the marking tip is directly controlled by hand. Such manipulation needs little practice and can be easily accomplished by students and occasional users. 
   In one preferred embodiment according to the present invention, a pen is integrated with the handle. 
   In another preferred embodiment according to the present invention, a mechanical pencil is integrated with the handle. 
   In another preferred embodiment according to the present invention, a pencil is utilized as a marking instrument and served as the handle. 
   The drawing compass of the present invention is easy to use, inexpensive, and simple to manufacture. 
   Additional features and advantages of the present invention are described in, and will be apparent from, detailed description of the preferred embodiments and from the illustrative drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  illustrates the use of one preferred embodiment of a drawing compass made in accordance with the present invention. 
       FIG. 2  is an exploded view of the drawing compass of  FIG. 1 , illustrating a pen attached on the lower end of the handle. 
       FIG. 3A  is a cross-sectional view taken along line  2 — 2  of the drawing compass illustrated in FIG.  1 . 
       FIG. 3B  is a fragmentary cross-sectional view of the drawing compass with a structure of ball bearing. 
       FIG. 3C  is a fragmentary cross-sectional view of the drawing compass with a structure of roller bearing. 
       FIG. 4  is an exploded view illustrating a modified form of the handle. 
       FIG. 5  is a cross-sectional view illustrated in  FIG. 4 , illustrating a mechanical pencil coaxially integrated with the handle. 
       FIG. 6  is an exploded view illustrating another modified form of the handle. 
       FIG. 7  is a partially sectioned side elevation view illustrated in  FIG. 6 , illustrating a pencil is utilized as the marking instrument and served as the handle. 
   

   DETAILED DESCRIPTION 
   Referring to the drawings wherein like numerals refer to like parts,  FIG. 1  illustrates the use of a preferred embodiment of the drawing compass according to the present invention. The drawing compass comprises an arm  10 , an elongated handle  20 , a marking instrument  60  mounted on the underside of handle  20 , and a pivot pin holder  40  slidably mounted on arm  10 . The arm  10  comprises an elongated bar portion  12  and a cylindrical portion  14 . Indicia may be placed on elongated bar portion  12  for setting desired radius, as illustrated in FIG.  1 . The handle  20  is rotatably mounted on cylindrical portion  14  of arm  10 . The vertical handle  20  and horizontal arm  10  form a shape of capital letter L. The pivot pin holder  40  is secured by a securing bolt  48  at a desired position on arm  10 . A pointed end  42  of pivot pin holder  40  is placed at the center of a circle  100 . The handle  20  is held and positioned substantially perpendicular to the drawing plane and moved along circle  100  to trace out a marking line. 
   As illustrated in  FIG. 2 , the handle  20  comprises a cylindrical handle base  22  and an extension sleeve  24 . The handle base  22  comprises an upper portion, a middle portion, and a lower portion. The upper portion of handle base  22  is externally threaded, and receives the internally threaded extension sleeve  24 . The middle portion of handle base  22  receives cylindrical portion  14  which has a throughbore formed therein for rotatably coupling to the middle portion of handle base  22 . The cylindrical portion  14  is retained between a collar  30  and a nut  36 , which coacts in threaded engagement with a threaded portion  32  of the handle base  22 . This forms a bearing structure which allows arm  10  to rotate freely while handle  20  is held during the drawing process.  FIG. 3A  is a cross-sectional view taken along line  2 — 2  of the drawing compass illustrated in FIG.  1 . Alternatively, other type of bearing structures may be employed.  FIG. 3B  illustrates the handle rotatable mounted on the arm with a structure of ball bearing. An annular recess  31  having an arc-shad section is formed on the middle portion of handle base  22  near collar  30  and another annular recess  33  is formed on the middle portion of handle base  22  near nut  36 . A plurality of balls  35  are interposed between the recesses and the opposite inner wall of cylindrical portion  14  such that arm  10  can rotate freely while handle  20  is held.  FIG. 3C  illustrates the handle rotatable mounted on the arm with a structure of roller bearing. An annular recess  37  is formed on the middle portion of handle base  22 . A plurality of cylindrical rollers  39  are interposed between recess  37  and the opposite inner wall of cylindrical portion  14  such that arm  10  can rotate freely while handle  20  is held. The various techniques to rotatably mount the handle to the arm are well known in the art. The lower portion of handle base  22  is externally threaded for receiving a marking instrument  60  through an internally threaded marking instrument holder  52 . The marking instrument such as a pen is frictionally fixed on marking instrument holder  52  through a central throughhole  54 . It will be understood that the marking instrument can be easily removed from the handle base, and the marking instrument can be changed, replaced or refilled. 
   The pivot pin holder  40  comprises a base  62 , a pivot pin  74 , and securing bolt  48 . The base  62  has a side opening dimensioned for slidably receiving elongated bar portion  12  of arm  10 . The base  62  further comprises a threaded bore  66  perpendicular to and communicating with the side opening such that securing bolt  48  may thread through throughbore  66  to engage arm  10 . The base  62  further comprises a boss  64  with an internally threaded bore for threadedly receiving pivot pin  74 . Indicia on bar portion  12  can be observed from a front opening  84  of pivot base  62  for setting the radius of a circle or arc to be drawn, as illustrated in FIG.  1 . The pivot pin  74  comprises a pin base and a pin extending vertically downwardly along the centerline of pivot base  62 . The pin base comprises a collar  80 , an upper externally threaded portion  78 , and a lower externally threaded portion  82 . In use, the upper threaded portion  78  is threaded on boss  64 . 
   As illustrated in  FIG. 3A , the cylindrical portion  14  of arm  10  is retained between collar  30  and nut  36  such that arm  10  is able to rotate snugly but can not move upwards or downwards along the longitudinal direction of handle  20 . The pivot pin holder  40  is secured by securing bolt  48  on a fixed position of bar portion  12  of arm  10 . The perpendicular distance from pointed end  42  to bar portion  12  is substantially equal to the perpendicular distance from the marking point to bar portion  12 . When the drawing compass is not in use, the pivot pin  74  can be removed from boss  64  and invertly threaded on the boss  64  such that pointed end  42  is encased in an aperture  68  at the centerline of pivot base  62 . It will be therefore understood that the pivot pin can be easily exchanged. It should be pointed out that, other technique of safety mechanisms may be employed to reduce the safety hazard of the pin, such as described in U.S. Pat. No. 6,311,404 to Smith. 
   FIG.  4  and  FIG. 5  illustrate a modification of the handle. The device shown in FIG.  4  and  FIG. 5  is different from the device shown in  FIG. 2  in that a mechanical pencil  90  is coaxially integrated with the handle base. The mechanical pencil  90  comprises an interior space  92  for storing spare leads. A plug  94  plugs a bore communicating with interior space  92 . The plug  94  may be an eraser or attaches to an eraser. A threaded collar  96  secures a lead  98 . Any other techniques for securing leads of mechanic pencils may be employed. As illustrated in  FIG. 5 , the upper portion of the handle base threadedly receives extension sleeve  24 . The cylindrical portion  14  is retained in the middle portion of the handle base between collar  30  and nut  36 . The mechanical pencil integrated with the handle base may coaxially rotate with the handle. When the compass is not in use, the handle sleeve  24  may be removed for easy storage or transportation. FIG.  6  and  FIG. 7  illustrate another modification of the handle wherein a normal pencil  110  is utilized as the marking instrument. The pencil  110  also serves as the extension sleeve. A handle base  120  comprises a cylinder  122  having an interior space defined by walls for receiving pencil  110  and securing means for retaining pencil  110  in a fixed position. The securing means comprises a securing bolt  124  threading through a female threaded bore on the cylinder for retaining the pencil  110  in a fixed position as illustrated in FIG.  7 . The cylindrical portion  14  is retained between a collar  126  and a nut  128 . The pencil  110  secured on handle base  120  should rotate snugly along the longitudinal axis of the handle base but should not wobble. Any other like securing means may be utilized for the purpose of securing the pencil to the handle base. 
   A critical aspect of the modification illustrated in FIG.  6  and  FIG. 7  is the position of the marking point of the marking instrument. The marking point must be pointed at the longitudinal axis of the handle base for accuracy and reliability. The diameter of the pencil should be coupled to the interior diameter of cylinder  122  of the handle base  120 . The relationship of the coaxial rotation of the pencil and the handle base should not be affected by the securing means. 
   As shown, the entire device can be dissembled very easily. The pencil can be changed with other marking instruments, such as a pen or a chalk. 
   The pin of the pivot pin holder can also be exchanged by disposable pins for ensuring center grasping force. 
   In use, the center point holder is adjusted to a desired radius by sliding along the elongated bar portion of the arm at a desired distance and secured to the arm by the securing bolt. The pointed end of the pin is placed at the center of the circle and the marking point of the marking instrument is placed at a start point of the circle. The handle is positioned substantially perpendicular to the drawing plane and moved along the radius of the circle as illustrated in FIG.  1 . As the pressure applied on the marking point is conveniently controlled by hand a circle or arc line is easily accomplished by one hand. 
   When the compass is not in use, the handle sleeve may be removed from the handle base for easy storage or transportation. The pin can be removed out and reversibly threaded on the base to encase the sharp pointed end for reducing safety hazard. 
   It is contemplated that the drawing compass of the present invention can be made of any metals, plastics and the like materials. Material of metals is preferred because weight of the compass aids to the pin from sliding away from the center point. The size and shape of the drawing compass can be varied widely for both functional use and appearance. The length of the arm is usually 3.5-5.5 inches for general use, which may be more than 5.5 inches for use in large working plane, depending on the size of the circle to be drawn. 
   It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the appended claims.