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CLOSE TOLERANCE SHAPING |
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February 14, 2024 |
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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. 
CLOSE TOLERANCE SHAPING - note the design "indexed" in the blank 0.25" from the deck from tail to wide point. Maximum depth of cut is 0.31" near the nose. The entire deck of this design is a close fit to the deck of the blank and is finished in the higher density foam near the skin of the blank maximizing the physical properties of the board's deck. 
OVER SHAPING - note the design is "indexed" close to the deck of the blank in the nose and tail 0.25" from the surface of the blank. The deck of the design at the wide point is 0.63" from the surface of the blank. The critical area of the deck of the design is cut so deep into the deck of the blank the physical properties of the board's deck are severely compromised. Correct blank selection, correct custom deck rockers, appropriate foam densities, and stringer selection are the key features and the foundation of close tolerance shaping. Close tolerance shaping is a crucial component of high quality custom surfboards. |
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