5.14.
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159
doubtful for most purposes. Conceivably, their harder edges might be a
significant factor in cutting certain types of materials, but this is not an
important factor under most circumstances. Conceivably, too, their edges
might last somewhat longer than the edges of soft glass, but most of the
time it seems as though contamination is what particularly destroys the
usefulness of a glass edge rather than physical damage to the glass
(Chapter 5.22). Thus, until truly satisfactory procedures are developed
for reproducibly breaking sheets of such glass their use is contraindicated,
except perhaps for very special purposes.
5.14. Knife Angle
For almost all biological material embedded in conventional plastics
it seems best that the knife be formed by an intersection of planes that
make as acute an angle as possible. The angle that actually exists precisely at the edge of a knife is of course difficult if not impossible to determine. It is evident, though, that the final deflection of a diagonal break
tends to make the angle of the edge more obtuse than the gross angle.
Thus, in making triangular knives, one ordinarily divides squares of
glass as uniformly as possible. If the knife edge is very close to an
original corner, its acuity may approach 45°, but will not realize it. If
the diagonal fracture deflects much below a corner, obviously the angle
of intersection will be more like 55°-60°.
Mr. A. Persson, referred to above as an engineer associated with the
LKB-Produkter Ab., has made a study of edge angles using refined
optical-reflection measurement techniques, and has told this writer that it
is almost impossible to produce an edge angle more acute than 52°. This
is true even if one attempts to bisect an original angle that is much less
than 90°. The final deviation of the advancing diagonal fracture nontheless prevents achieving acuity beyond 52°! The possible exception to this
might be "cross-over" breaks, in which the diagonal fracture starts
deflecting toward one side of the corner, and then passes across the
corner itself to the other side. Presumably, there must be at least a small
zone in such knives that would truly represent the bisection of the
original angle. However, it is not ordinarily practical to try using such
knives. In summary, then, the most acute knife that one can hope for
has an angle of approximately 52°, and it is not worthwhile trying to
bisect angles of much less than 90° in an effort to produce more acute
KNIFE ANGLE
159
doubtful for most purposes. Conceivably, their harder edges might be a
significant factor in cutting certain types of materials, but this is not an
important factor under most circumstances. Conceivably, too, their edges
might last somewhat longer than the edges of soft glass, but most of the
time it seems as though contamination is what particularly destroys the
usefulness of a glass edge rather than physical damage to the glass
(Chapter 5.22). Thus, until truly satisfactory procedures are developed
for reproducibly breaking sheets of such glass their use is contraindicated,
except perhaps for very special purposes.
5.14. Knife Angle
For almost all biological material embedded in conventional plastics
it seems best that the knife be formed by an intersection of planes that
make as acute an angle as possible. The angle that actually exists precisely at the edge of a knife is of course difficult if not impossible to determine. It is evident, though, that the final deflection of a diagonal break
tends to make the angle of the edge more obtuse than the gross angle.
Thus, in making triangular knives, one ordinarily divides squares of
glass as uniformly as possible. If the knife edge is very close to an
original corner, its acuity may approach 45°, but will not realize it. If
the diagonal fracture deflects much below a corner, obviously the angle
of intersection will be more like 55°-60°.
Mr. A. Persson, referred to above as an engineer associated with the
LKB-Produkter Ab., has made a study of edge angles using refined
optical-reflection measurement techniques, and has told this writer that it
is almost impossible to produce an edge angle more acute than 52°. This
is true even if one attempts to bisect an original angle that is much less
than 90°. The final deviation of the advancing diagonal fracture nontheless prevents achieving acuity beyond 52°! The possible exception to this
might be "cross-over" breaks, in which the diagonal fracture starts
deflecting toward one side of the corner, and then passes across the
corner itself to the other side. Presumably, there must be at least a small
zone in such knives that would truly represent the bisection of the
original angle. However, it is not ordinarily practical to try using such
knives. In summary, then, the most acute knife that one can hope for
has an angle of approximately 52°, and it is not worthwhile trying to
bisect angles of much less than 90° in an effort to produce more acute