186. Four rods are jointed
together to form a parallelogram, the sides of which can be lengthened or
shortened to suit the scale of reproduction. One is attached by a fixed
pivot at a to the board on which the drawing is done. At b and e are
removable pivots, used for adjusting the rods; at c is a pivot which
projects an inch or so below the rods. The pointer is inserted at d for
enlargement, or at f for reduction, the pencil being in the unoccupied hole
at d or f.
If a same-sized copy is desired, the fixed pivot is transferred to d, and
the pencil and pointer placed at a and f respectively.
Construction of an Enlarging and Reducing Pantograph.--Cut out of
1/8-inch oak, walnut, or beech four rods 5/8 inch wide and 19 inches long.
Smooth them well all over, and make marks near the ends of each, exactly 18
inches apart. The graduation of the rods for the adjustment pivot holes is
carried out in accordance with the measurements given in Fig. 187. It is
advisable to mark out and bore each rod separately if you do not possess a
machine which will drill holes quite perpendicularly; if you do, all four
rods can be drilled at one operation.
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