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Close tolerance shaping is one of the key features of the highest
quality polyurethane core polyester skin surfboards. One of the great
features of the contemporary very light, close tolerance, molded
polyurethane surfboard blank is the higher density foam near the deck
and bottom of the blank and the lower density foam of the core. When
employed correctly this feature makes a very high strength to weight
ratio surfboard. In the 20 years from 1985 to 2005 Clark Foam's
strength to weight ratio increased dramatically in part due to a wide
variety of close tolerance blanks and an extensive rocker program
across all classes of surfboards. There's always the potential of
substandard inferior quality surfboards caused by shaping machines
machining too deep into blanks or shaping too deep into blanks with
hand tools due to using blanks that do not feature deck rockers that
mimic or approximate the surfboards deck rocker. This is referred to
as over shaping. Over shaping, particularly on the deck, compromises
the principle of close tolerance shaping and the physical properties
of the deck by shaping through the higher density skin and into the
lower density core. Over shaping polyurethane polyester surfboards by
machine or with a planer yields a surfboard with a short performance
and durability lifespan. Additionally, over shaping yields not only a
weaker surfboard with diminished physical properties, but also a
heavier board as the lower density core foam absorbs notably more
resin in the laminating process.
Over shaping is such a significant issue in polyurethane
polyester surfboards. It's a problem that existed long before CNC
shaping machines. As noted, the nature of molded polyurethane
surfboard blanks includes higher density foam on the skin and near
the surfaces of the top and bottom of a blank with decreasing density
towards the core of a blank. Whether machine shaped or hand shaped
poor blank selection, non aligned rockers, and inadequate stringers
or improper stringer glue ups are core contributors to over shaping.
It is essential that the deck rocker of a design mimics the deck
rocker of a blank in a manner that maximizes the physical properties
of the deck.
Gordon "Grubby" Clark at Clark Foam was constantly focused on the
physical properties of polyurethane foam surfboard blanks and PU /
Poly surfboards. His observations coupled with critical thinking
initiated the concept of close tolerance shaping. Grubby introduced
multiple blank molds, foam densities, stringer options, and a robust
custom rocker program. US Blanks is equally committed to close
tolerance shaping. They maintain and expand an extensive variety of
blanks, densities, stringers, and rockers.
The maximum density of a polyurethane blank is at the skin. The
density decreases in the core of the blank. The deeper the finished
shape from the skin of a blank the more the physical properties of
the blank or core of a board are compromised. This is particularly a
problem for the deck of a board due to the constant paddling and
surfing impacting the deck.
An appropriate blank and correct deck rocker with corresponding
deck rockers of surfboard and blank are fundamental to maximizing the
physical properties of the deck of a PU / Poly surfboard. It is
essential for shapers to design custom deck rockers for blanks that
match the deck rockers of their designs. |
