US2420090A - Straightedge protractor - Google Patents

Description

y 6, 1947. P. A. NELSON 2,420,090

STRAIGHT EDGE PROTRACTOR Filed June 25, 1945 INVENTOR. PA 1 A. NELSON ATTORNEY Patented May 6, 1947 UNITED STATES PATENT OFFICE STRAIGHTEDGE PROTRACTOR Paul A. Nelson, Lake Grove, Oreg.

Application June 23, 1945, Serial No. 601,240

1 Claim. 1

This invention relates generally to drawing instruments and particularly to a straight edge protractor.

The main object of this invention is to provide a convenient form of drafting instrument whereby the making of drawings may be greatly facilitated, and in which the device may be attached to an ordinary drawing board without regard to the straightness of its edges.

The second object is to provide a straight edge in which the blade of the square may be set at any desired angle and held in that position as long as desired.

The third object is to make it possible to swing the blade away from the drawing in order to give better access to the board for the placement or removal of the drawing.

These and other objects are accomplished in the manner set forth in the following specification, as illustrated in the accompanying drawing, in which:

Fig. 1 is a perspective view of the device.

Fig. 2 is a front elevation of the device.

Fig. 3 is an end elevation of Fig. 2.

Fig. 4 is a plan of Fig. 2.

Similar numerals refer to similar parts throughout the several views.

Referring in detail to the drawing there is shown a board 10 under whose lower side H is secured a Z bar !2 from the lower end of whose vertical portion I3 is formed the horizontal outwardly turned flange M. The bar I2 is securely fastened to the under side of the board by means of the screws l5.

On the under side flange M is disposed a horizontal plate !6 which is hingedly joined to a plate 17 by means of a pin IB. Secured on the plate It and at opposite ends thereof are the rollers l9 which engage the portion l3 above the flange l4.

Also mounted on the plate I 6 is a roller 20 whose bolt 2| is mounted in a slot 22 in the plate 16 in order that it may be urged by the spring 23 which is secured to the bolt 2| and to the rivet 2% in the plate is in order that the roller 2!! may be urged toward the vertical portion I3. It is immaterial which of the rollers is made movable, it being merely important that they be relatively movable.

Secured to the plate I! is the side 25 of the angle plate 26 which contains a calibrated semicircular edge 21 and the semi-circular slot 20 which is concentric with the edge 21. The straight edge 29 is pivoted on the rivet 30 and is clamped by means of the knurled nut 3| whose bolt 32 passes through the slot 28.

An indicating plate 33 provided with a Vernier 3:4 is secured to the straight edge 29 by means of the rivets 35.

The operation of the device is as follows:

Assuming that the member [2 is securely fastened to the board l0 and that the rollers l9 and 20 engage opposite sides of the membersl3 lt i only necessary for the draftsman to swing the straight edge l9 to the position shown in Fig. 1 and set the square 29 at any desired angle under the control of the knurled nut 3|. Obviously the rollers l9 and 20 are free to roll along the member l3 and guide the square 29 accurately along the surface of the board.

While I have thus illustrated and described my invention, it is not my intention to be limited to the precise form shown herein, but to cover all such forms and modifications thereof as fall fairly within the appended claim.

A straight edge of the class described characterized by having an elongated track of 2 bar cross section adapted to be fastened to the edge of a drawing board, a carriage mounted on said track and having rollers for engaging opposite sides thereof, a side roller having a spring for urging same toward said track, an angular plate one side of which is normally vertical and hinged to said carriage and the other side of which is normally horizontal and extendable over the drawing board, said horizontal portion having a semi-circular graduated edge, a straight edge hinged to said horizontal portion at a point concentric with said graduated edge, and means for clamping said straight edge to said horizontal member.

PAUL A. NELSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,031,665 Poeklington July 2, 1912 FOREIGN PATENTS Number Country Date 238,718 German Oct. 3, 1911

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