Patent GB-726473-A (GB)
Title: Improvements in draughting machines
Inventor: HOLLIS HAROLD FRANCIS
IPC: B43L13/14
Filed: 1953-05-29
Abstract: 726,473. Draughting machines; pantographs. NORTH THAMES GAS BOARD. May 29, 1953, No. 15093/53. Class 97 (3). A perspective drawing appliance comprises a master pantograph having a tracer point and a follower point which reproduces to a different scale the path taken by the tracer point, a setting arm pivoted to the follower point and an operating arm pivoted to the tracer point, and means for constraining a point on the setting arm to slide along the operating arm. This appliance can be used with any predetermined vanishing point provided the setting arm is held parallel to the line joining the pivot point of the pantograph with the vanishing point. Such parallelism may be maintained automatically by a mechanism such as shown in Fig. 2. In this Figure, a pantograph RSTVWX identical with a pantograph ABCDEF is linked thereto at DV and HY, A and R being the pivot points of the two pantographs, H and Y two follower points and C and T two tracer points, H J being the setting arm and C L the operating arm. The link HY and the line joining C and T are arranged to remain parallel with the line AR joining the pivot points. The line AR remains at a fixed angle to a horizon line PQ so that HY also remains at said fixed angle and JH may therefore be set at a fixed angle to PQ by rigidly securing it to link HY. If JH is thus set parallel to AK, the line joining the pivot point A to the vanishing point K, it will always remain parallel thereto. Links AB, BC and EH may be removed. Such an apparatus in the form of a drafting machine is shown in Fig. 4. In this machine there is a master pantograph comprising pivoted bars 1, 2, 3 and 4 in the form of a parrallelogram linkage, a bar 5 having slides 11, 12 movable over bars 2, 4 and a bar 6 having slides 13, 14 movable over bars 1, 3, this pantograph being pivoted at 7 to a bracket 15 attached at 16 to a drawing board 17. Pivoted at 24 to the bracket 15 and at 25 to a rightangled bracket 26 pivoted at 10, is a bar 23, and a bar 27 is pivoted at 28 to the bracket 26 and at 29 to a structure 19, the bars 23, 27 and the bars 3, 4 forming with bracket 26 a linkage for maintaining the structure 19 at a predetermined angle to an edge of the drawing board 17. A bar 30 is pivoted at 31 to bracket 15 and at 28 to bracket 26; one end of a bar 32 is mounted in a slide 33 pivoted to a slide 35 movable along bar 30, the other end of this bar being pivoted at 36 to a link 37 pivoted at 38 to a slide 39 adjustable on bar 6. The bars 30, 32 and link 37 form a part pantograph, similar to the part pantograph A C D F H. Link 37 comprises a protractor 40, centred at 36 and a setting arm 41 is pivoted at 36 and is adapted to be secured at any angle by a clamp 42. The setting arm 41 is also pivoted to a slide 45 adjustable along an operating arm 46, pivoted at 29 to the structure 19. A straight edge 47, pivoted at 48 to the structure 19, is maintained parallel to operating arm by a link 48<SP>1</SP>. A similar part pantograph is provided by bars 53, 54 and a link 59, this part pantograph having a setting arm 63 pivoted to a slide 67 adjustable on an operating arm 68 with which a straight edge 69 is maintained parallel by a link 21. The machine is held slightly above the drawing board by an adjustable support 79,