US2436392A

US2436392A - leshner

Info

Publication number: US2436392A
Authority: US
Publication date: 1948-02-24
Anticipated expiration: 1965-02-24

Description

Feb. 24, 1948. E. LESHNER PLOTTING BOARD AND PROTRACTOR SQUARE Filed March 22, 1946 INVENTOR. ErV/n L eg/rner 65 4, fi/VD HTTOC/VEYS Patented Feb. 24, 1948 PLOTTING BOARD AND PROTRACTOR SQUARE Ervin Leshner, Philadelphia, Pa.

Application March 22, 1946, Serial No. 656,239

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 2 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to plotting devices and particularly to a protractor T-square having a novel locking feature.

In using a conventional T-square or a protractor T-square where accuracy is a requirement, the head of the T-square must be kept constantly against the end of the drawing board or have a similar guide. This requires the constant use of one hand, leaving only one hand to manipulate the pens, pencils or other drafting equipment.

Moreover, for certain kinds of work the blade of a T-square may preferably be momentarily locked in a fixed position with respect to the board and, for rapid operation, any locking means which is provided must necessarily be operative in minimum time and with minimum effort.

It is therefore an object of this invention to provide a self locking means for a T-square whereby, if the free end of the blade is raised very slightly from the face of the board when about to move it on the board from one place to another, the T-square is automatically unlocked, and when the blade is put flat on the board in a position in which it is to be used, the blade is automatically locked.

Other objects and advantages will be evident when the following description is considered with reference to the drawing, wherein Fig. 1 is a top plan view of a fragment of a drawing board and a protractor T-square embodying the principles of my invention;

Fig. 2 is a longitudinal section taken at 2-2 of Fig. 1 through the guide and locking means as it appears when the T-square is in the locked position.

Fig. 3 is a view like Fig. 2 except that the locking means is in the unlocked position.

Like reference characters refer to like parts throughout the several views.

In the drawing, a drawing board has a channel shaped rail 12 extending along one edge and is fastened to the board by screws l4. Additional guide rails l2 may, of course, be provided for other edges of the board if so desired.

The T-square has a blade l6 preferably of transparent plastic material pivotally attached to a sheet metal head l8 by a hinge pin 20. A bolt 22 extends through a hole in the blade IB "and through an arcuate slot 24 in the head IS. A thumb nut 26 on the bolt 22 clamps the blade and head together at any selected angle. The inner edge of the sheet metal head It is bent downward to form a guide surface l5 for guiding the head along the upper inner edge of the rail 12, and is curved outward so that the end II will 2 bear with considerable pressure against the inside of the rail and form a clamp for holding the head it in any desired position on the rail 12. The outer edge of the head l8 has a degree graduation 23 extending from 0 to 60 degrees in either direction from the zero position shown. A line 30 on the underside of the blade [6 is alignable with the degree graduation to indicate the angle selected. The operation of the device is as follows:

When a line is to be drawn along an edge of the blade it, the blade is allowed to lie fiat on the board 10 as in Fig. 2. In this position the clamping end I! holds the guiding edge l5 tightly against the upper edge of the rail l2. When the desired line has been drawn and the T-square is to be moved, it is only necessary to tilt the blade as in Fig. 3 whereby the clamping end I! is withdrawn from the rail l2, permitting the head 3 to be moved to the next position. The amount which the blade must be tilted to free the head 58 so that it can be moved, is greatly exaggerated in Fig. 3 for purposes of illustration. A very slight tilt of the blade only will free the head so that it will slide along the rail.

While I have shown and described a single exemplification of my improved plotting board and protractor square, it will be understood that changes may be made, as for instance changes in the form of the clamping means, without departing from the spirit of the invention, to define which, I claim:

1. In combination, a plotting board, a T-square, a channel shaped rail secured to the board along one edge, and a guide and clamping part extending downward from the underside of the head of said T-square into the channel of said rail, said guide and clamping part bearing tightly near the top edge of that side of the channel which is nearest the'board and nearer the bottom on the other side of the channel, whereby said T-square is locked against movement on said board when said T-square lies flat on said board and free to move on said board when the outer end of the head of said T-square is tilted downwardly.

2. The device defined in claim 1 wherein the side of the channel farthest from said board is less in height than the side nearest said board.

ERVIN LESHNER.

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

Giehler "a--- Nov. 19. 1929