While the cone principle is the all encompassing physics law in flintknapping, the center-line
concept is the most important principle to understand.  Failure to understand the center-line concept
will bring a lot of trouble and frustration to the beginning flintknapper.

    If you take your piece of flint or chert and imagine that it was cut perfectly in half by a rock saw.
Where the saw traveled, cutting the piece exactly in half, is the center-line of the piece you are
trying to knap.  You can
ONLY take good flakes off BELOW the center-line of the piece you are
knapping.  If you attempt to take flakes off above the center-line, your piece of flint or chert will
likely crush, hinge fracture, or snap in a near straight line across the piece starting where you
attempted the flake removal.

   While knapping your biface, you will notice that the edge waves up & down due to flaking.  These
dips and raises are above, below, and sometimes right at the center- line of the biface.  Look for the
parts of the edge that dip below the center of the biface and plan to take your flakes off from those
areas.  If you find an area where a flake needs to be taken off, and the edge rises above the center-
line of the biface, take your pressure flaker and take small flakes off so as to lower the edge below
the center-line - then abraid it - and strike the flake off.

   90% of the time when you fold a biface (snap it in half), if you put the two pieces back together,
and look at the place you struck, it was likely above the center-line of the biface.  When considering
the center-line concept, being safe is better than being sorry.  When you are a new flintknapper,
take extra time to be sure your platform striking area is well below the center-line.
Answer
Center Line
Center Line
Below Center Line
Above Center Line
Good Striking
Platforms
Good Striking
Platforms
Bad Striking
Platforms
x
x
x
x
x
x
Abraid the good platforms and strike off flakes