Claims
- 1. A drafting instrument for forming circles comprising:
- a support member having an upper surface, a lower support surface and an inner edge forming a circular opening of given diameter;
- a bearing surface formed on said inner edge of said support member;
- a circular disk member of a diameter slightly less than said given diameter so as to be rotatably received on said bearing surface in a position vertically spaced from said support surface;
- an incremental circle guide slot having first and second edges formed in said disk member, said slot located to begin adjacent to a center point of said disk, to extend along a line parallel with a radii of said disk member and to terminate at a point adjacent to the circumference of said disk;
- said slot having a plurality of wedge-shaped notches of equal size and equal spacing and which include generally straight circumferentially extending surfaces facing said center point and forming an acute angle at their apexes with intersecting surfaces of said notches, said notches being arranged along at least one of said first and second edges;
- said first and second edges being spaced at a width sufficient to receive and positively locate a forming point in said apexes so that said point is disposed entirely within one of said notches and is contacted only by said circumferentially extending and intersecting surfaces; and
- whereby upon exertion of pressure in a direction outward from said center point, said disk is rotated and a circle of selected size is accurately formed.
- 2. The device of claim 1 wherein said wedge-shaped notches are formed along said first and second edges.
- 3. The device of claim 2 wherein said wedge-shaped notches along said first and second edges are arranged to provide circumferentially offset apexes which incrementally locate said forming point at increments radially along said disk member.
- 4. The device of claim 1 wherein said wedge-shaped notches are spaced along said one of said first and second edges at intervals of 1/16 inch.
- 5. The device of claim 1 wherein said slot is up to 5 inches in length.
- 6. The device according to claim 1 wherein said disk is transparent and includes a plurality of diameter indicating lines arranged on said disk.
- 7. The device according to claim 1 wherein measuring indica is arranged on said upper support surface adjacent to said circular opening.
- 8. The device according to claim 1 wherein alignment cross lines are arranged on said disk member, said lines passing through said center point and being disposed at 90.degree. to each other.
- 9. The device according to claim 1 wherein the support member is formed of first and second plastic plates, said bearing surface being formed in said first plate.
- 10. The device according to claim 9 wherein said second plate is formed of clear plastic and is secured to said first plate member so as to extend above measuring indicia and said bearing surface thereby covering said indicia while securing said disk in said bearing.
- 11. The device according to claim 1 wherein said bearing surface is formed as an L-shaped shoulder having a vertical peripheral surface and a horizontal surface, individual bearing members arranged about an apex formed by said peripheral surface and said horizontal surface, said bearing members engaging an outer edge of said circular disk to position said disk horizontally spaced from said peripheral surface and vertically spaced from said horizontal surface.
- 12. The device according to claim 1 including a plurality of incremental circle guide slots spaced circumferentially about said disk, said slots having said wedge-shaped notches radially spaced and offset from one another to provide an increased number of circle drawing increments.
- 13. A drafting instrument for forming circles comprising:
- a support member having a bearing surface for rotatably receiving a disk member;
- an incremental circle guide slot having first and second edges formed in said disk member and extending from a point adjacent to the center point of said disk to a point adjacent to the circumference of said disk;
- said first and second edges being spaced at a width sufficient to receive and positively locate a forming point;
- said first and second edges being provided with a plurality of wedge-shaped notches having apexes arranged to be offset from each other so as to allow each notch to locate said forming point at an incremental radial location relative to the center point of said disk;
- whereby upon rotation of said disk a circle of selected size is accurately formed.
- 14. The device of claim 13 wherein said bearing surface is raised relative to a lower support surface of said support member to elevate said disk above a circle forming surface.
- 15. The device of claim 13 wherein the disk member is formed of clear plastic which is provided with a plurality of diameter indicating lines and measuring indicia.
- 16. The device of claim 13 wherein said wedge-shaped notches including generally straight circumferential surfaces forming an acute angle at said apexes for confining said forming point.
- 17. The device according to claim 13 including a plurality of incremental circle guide slots spaced circumferentially about said disk, said slots having said wedge-shaped notches radially spaced and offset from one another to provide an increased number of circle drawing increments.
- 18. The device according to claim 13 wherein protractor measuring indica is arranged on said upper support surface adjacent to said circular opening.
- 19. The device according to claim 13 including diameter measuring indicia arranged on said disk around a periphery thereof in proximate relation to said guide slot for selecting a notch corresponding to a desired diameter.
Parent Case Info
This is a continuation of copending application Ser. No. 07/497,974, filed on Mar. 23, 1990, now abandoned.
US Referenced Citations (13)
Foreign Referenced Citations (4)
Number |
Date |
Country |
217974 |
Apr 1987 |
EPX |
334695 |
Mar 1921 |
DE2 |
8904770 |
Jun 1989 |
WOX |
746099 |
Mar 1956 |
GBX |
Continuations (1)
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Number |
Date |
Country |
Parent |
497974 |
Mar 1990 |
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