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The hyperbolic paraboloid, saddle or Pringle's potato chip, is one of
the more difficult shapes to make. Look at Heikki Seppa's diagram. He
divides a square into quadrants, either from corner to corner, or
from side to side. The final shape is different depending on which
one you start with. In quadrants 1 and 3, forge the metal on a flat
steel bench block so that the edge curves outward away from the
center of the square. The cross-hatches on his diagram are the
hammer blows. Flip the blank over, and do the same for quadrants 2
and 4. Note that the blank is still flat when you are done. You have
merely stretched the edges. You need to keep up with the quadrants as
you raise the blank on a sinusoidal stake. 1 and 3 will curve toward
each other above the stake and 2 and 4 toward each other below the
stake. Final closure is via planishing against a round mandrel.
Remember to anneal early and often. 20 gauge or thicker for this one
because of the stretching.
Anticlastic cuffs and variations thereof are much easier and it
sounds like you have done these.
Good luck.
Emie Stewart
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