Geometrical instruments – Straightedge type – Base attached
Patent
1980-01-15
1982-11-23
Phillips, Charles E.
Geometrical instruments
Straightedge type
Base attached
B43L 1308
Patent
active
043598242
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The invention relates to drawing apparatus, particularly a protractor unit for drawing board, which comprises, on either side of a support, two portions interconnected by a hub extending through said support, which consist on the one hand of a rule carrier and on the other hand of a handle for rotatably driving the rule carrier and a graduated plate registering with at least one scale.
BACKGROUND OF THE INVENTION
The known apparatus comprises a number of predetermined angular positions, as a rule at 15-degree intervals, and the snap engagement in the selected position is obtained by engaging a pawl into a notch of a suitable crown.
Other manufacturers obtained this indexing function by means of balls urged by springs into holes disposed at spaced intervals along the periphery of a circular plate.
The known devices have in common the same difficulties to be solved:
SUMMARY OF THE INVENTION
The scope of the present invention consists in providing an accurate ratchet device which can easily be engaged in each predetermined angular position, without play and with a long useful life, and the manufacture of which is not attended by specific difficulties.
To this end, the protractor unit according to the invention is characterised by the fact that each of the two relatively rotatable portions comprises a toothed circular plate concentric to its axis of rotation, turning in a same plane, each provided with the same number of radial teeth, and by the fact that a third circular plate, having the same number of teeth, concentric to the other two, is provided with means whereby its teeth can be interposed between those of the other plates, so as to lock the handle and rule carrier in a predetermined angular position relative to the support.
The essential advantage provided by the protractor unit according to the invention lies in the fact that the ratchet function is obtained by the engagement of all the teeth of the intermediate plate into all the teeth of the other two plates, thus warranting a high degree of precision free from play due to a long service.
BRIEF DESCRIPTION OF DRAWINGS
Other advantages will appear as the following description of a preferred but not limiting form of embodiment proceeds with reference to the drawing, in which:
FIG. 1 is an exploded sectional view,
FIG. 2 is an exploded section showing a modified form of embodiment,
FIG. 3 is an exploded perspective view of the ratchet means.
DESCRIPTION OF PREFERRED EMBODIMENT
The protractor unit according to the invention consists essentially of a so-called fixed portion comprising a support C, the bearing socket B carried by a support C which is provided in turn with a toothed plate or gear 1, and of a turning portion comprising a handle D provided with a smaller toothed plate or gear 2 and connected with a rule carrier A by a hub E rotatable in the bearing socket B.
The toothed plates 1 and 2 are concentric to the hub E and plate 2 lies in an annular recess 1a in plate 1 so that the toothed portions of the plates lie in a common plane parallel to the rules.
A third toothed plate or gear 3 provided with the same number of teeth as, and concentric and parallel to plates 1 and 2 is, movable by springs 4 into meshing engagement with plates 1 and 2 making them integral with each other.
This plate 3, movable along the hub E, is suspended from a small plate 7 by means of columns 8 extending through the base 9 of control handle D and turning therewith as is conventional, at the periphery of the base 9 there is a graduated scale 9a cooperating with an index on the support C.
The upward or downward movements of plate 3 are obtained by means of a pressure exerted on a pusher 5 incorporated in the handle D. The translation of pusher 5 actuates a two-armed lever 6 having a bearing point 60 located on said base 9 beneath the small plate 7. The arm 61 of lever 6 is pivotally connected through a pivot pin 51 to pusher 5 and extends through an elongated aperture 70 formed in small plate 7 so that its short arm 62 bears against the ce
REFERENCES:
patent: 2900728 (1959-08-01), Wallace
Adams Bruce L.
Alpia S.A.
Burns Robert E.
Lobato Emmanuel J.
Phillips Charles E.
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