|
He replied: The curl is oriented
on that particular piece non-perpendicular to the
longitudinal grain. The result is, when turned to a
cylinder, it produces a spiral/helical sort of figure. The
spiral/helix curl is a function of the orientation of the
curl and of the piece being turned into a cylinder. The
"curly birch" photo, attached, is an off-cut from the board
from which your big ruler was made. Note the relatively
longitudinal orientation of the curl in that board. Compare
it to the relatively perpendicular curl in the pieces on the
left. For many applications, it is prized to have the curl
exactly perpendicular to the grain. In
the curly birch and maple photo, attached, you'll see the
maple, on the right, has a curl that is perpendicular to the
grain of the piece. Turning the maple, with its orientation
of curl, produces "rings" rather than spirals.
The other pieces of birch that I
have, specifically chosen to be curly, don't have the curl
oriented as in the piece I used for your big ruler. I don't
know if the orientation of the curl in your big ruler is
especially rare, or it is relatively more common in birch
than other woods. I
usually try to buy wood that has the curl running
perpendicular to the grain. It might be interesting to see
what woods I can find with a curl running less
perpendicular. Maple usually has curl that is close to
perpendicular. Doing an interweb search, there do appear to
be a few examples of curly birch similar to what I used on
your big ruler. There are no examples that I can find of
maple that have an almost longitudinal curl to it. Could be
an interesting characteristic of some birch.
  |