Considering part of body and the direction of cutting the leather

[genepinefield]

Hello,
When you cut leather, do you consider the part of body and the direction of cutting? If so, what are you doing?

Generally, the back side is hard and the abdomen to the legs are soft.

As for the direction, it's said that it don't stretch vertically from the head to the buttocks, but stretches horizontally.

ex. Leather stretch area
https://howtoshoes.blogspot.com/2014/05/basic-of-shoes-leather-upper.html

Edited October 29, 2020 by genepinefield

[Dana Johnson]

When I make bellows I think carefully about the “grain” direction. In the top and end runs I want the stretch direction to be across the strip, rather than lengthwise. As the leather bends at the peaks I want it to be more flexible.  I save most of the backs on my skins for that, while the gussets are better far down the sides and near the belly.  Butterflies are not grain critical and easily use up the remaining areas of the skin.
   For reed valves, the grain should be in the long direction of the valve.  This means the valve resists bending more and will tend to snap back to flat, where the other orientation can result in a limp floppy valve.

   For hand straps, these should be cut with the grain oriented along the length, or the leather will stretch, and be vulnerable to cracking and tearing.

   Grain changes direction on the hide, and you want to think about it’s job on the animal who made it.  There is little need for stretch along the spine or down the sides about half way down. Beyond that, the hide stretches for breathing and at the belly, for eating and holding the guts in.  On the lower sides, the stretch becomes more omnidirectional the farther you go from the spine.  I like to use this part for gussets, and the parts that just get glued to the card stock.  
   Different leathers have different stretch issues.  Goat and calf are similar in their grain, as is sheep, though I have found that while goat is quite strong, sheep that I have used is weak cross grain and tears more easily.  Hair sheep (as opposed to wool sheep ) seems to be more like goat.  Kangaroo seems equally stretch resistant in all directions.

    Grain counts, and if I am using leather that the position on the hide isn’t known, I cut a narrow strip in a couple directions and see which stretches.  If I am cutting up a skin for valves, I take a marker and lightly draw arrows indicating the grain direction so I can use it later.  
Dana