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Anatomy of a Ski

Anatomy of a Ski

How to decode a ski’s inner workings—and what it means to you
posted: 07/22/2009
Two common constructions: laminate or "sandwich" (top) and cap (bottom).

Ever wonder what's under that topsheet, or how a ski is actually made? With a few exceptions, most skis are put together using two or three basic construction techniques and incorporating the same basic ingredients. Here's how wood, plastic, foam, steel and a dose of designer ingenuity come together to get you down the hill reliably.

By Joe Cutts

 

BASIC CONSTRUCTION TYPES

Cap (pictured at top) The top layer(s) arch from one edge to the other, so that the top of the ski is rounded, rather than flat. Sometimes the topsheet is reinforced and plays a structural role (a “load-bearing cap”), but usually it’s cosmetic, with performance attributes determined by core design. Though typically a less expensive construction, cap skis vary widely in performance and price.

Laminate or “sandwich” (pictured at bottom) Prized for its power and edge-hold. The ski is built—or “laid up”—in horizontal layers. Typical laminate construction: base sheet, then a sheet of pre-preg fiberglass, then a sheet of metal, then the core, then metal, then fiberglass, then topsheet.

Torsion box (not pictured) The core, usually wood, is encased in fiberglass, then epoxy-soaked and cured. So named because it resists twisting (see “torsional rigidity”). Some companies believe it produces a lighter ski—no metal needed—without sacrificing edge-grip.

ANATOMY

Topsheet The top layer of a ski, typically a sheet of clear plastic with the ski’s graphics printed on its underside

Laminates Sheets of reinforcing material—usually metal or fiberglass fabric—layered above and below the core. Metal laminates tend to make a ski more damp and stable; fiberglass light and lively.

Core The primary structural element—wood or foam—around which the ski is built. Some foam cores (the good ones) are milled to precise shapes from foam blanks, then laid into the ski mold; other foam cores (derisively known as “squirties”) are simply injected through the tail into a hollow shell of a ski (a cheap and imprecise manufacturing method). Wood cores—which are generally heavier, more durable and more damp—are made by laminating vertical strips of wood together (think plywood tipped on edge).

Sidewall The vertical plastic side of a laminate-construction ski. Differing densities of material yield different performance characteristics between skis.

Base A sheet of plastic, usually high-density polyethylene. Typically “structured” with micro-grooves that help to reduce suction and promote glide.

Edge A strip of stainless steel integrated into the layup

GLOSSARY

Camber The convex curvature built into the length of a ski. Distributes the pressure of a skier’s weight to the tip and tail, giving the ski more grip on the snow.

Rocker The opposite of camber, curving upward off the snow, fore and aft. Used in powder-specific skis for better float and ease.
 

Dampening The reduction of the vibrations that occur when a ski is in motion. A dampened ski is better able to hold an edge in the snow—but might lack liveliness.

Dimensions Tip, waist and tail widths—an expression of the shape of a ski
 

Midfat A loosely defined category of skis, prized for their versatility. They’re not as wide as specialized powder skis, nor as narrow as speed or race skis. Today’s midfats—typically 80 to 90 mm at the waist—are generally wider than those of recent years.
 

Mold A metal plank with a ski-shaped cavity milled into it. Typically, ski components (and liberal amounts of epoxy) are placed into the mold, which is then subjected to intense heat and pressure to bond the components and squeeze out excess epoxy.
 

Pre-preg A type of prefabricated laminate used to reinforce ski cores. Sheets of fiberglass fabric are impregnated with epoxy, cured, then cut to fit the ski’s width and placed in the mold.
 

Sidecut The narrowing of a ski at its waist; aids in turning when the ski is tipped on edge and pressured into an arc
 

Sidecut radius A measurement, in meters, of the depth of a ski’s sidecut curvature. The curve is extrapolated into an imaginary circle, and the radius of that circle describes the ski’s sidecut.
 

Taper The difference between the tip and tail widths. A ski with a greater taper generally initiates arcs easily, resulting in a turnier ski, while a ski with a smaller taper is less “hooky” and easier to skid.
 

Titanal The brand name of the aluminum alloy most commonly used in metal laminates
 

Titanium A lustrous white metal prized for its strength-to-weight ratio; occasionally alloyed with aluminum for use in laminates
 

Torsional rigidity A ski’s ability to resist twisting, often achieved by aligning glass fibers across the core at a 30-
to 45-degree angle (see “torsion-box construction”). By increasing torsional rigidity, a manufacturer can make a lighter, metal-free ski that still holds an edge on hardpack.

HOW A SKI IS MADE

We can’t help thinking about panini. You know how they’re made: layers of bread, meat and cheese, squished and cooked into cohesive goodness by a heated press. The best skis (those not made by injecting foam into a shell) are made in a similar fashion.

Instead of prosciutto di Parma and fontina, of course, we’re talking less tasty ingredients: plastics, wood, metals, fibers. Instead of melted cheese to hold it all together, there’s epoxy. And rather than using a panini mold, we’ll use a high-powered press designed to accept various ski molds (see Glossary).

A factory worker starts with an empty mold and a supply of all the components needed to build skis of a certain length, shape and design. Into the mold go the ingredients, layer by layer: base and edge material on the bottom, then the vertical sidewalls over the edges, a couple of reinforcing laminates over the base (typically Titanal and/or pre-preg fiberglass) then the precisely milled core (wood, foam or a combination, sometimes wrapped in fiberglass, as in torsion-box construction). Above the core go one or two more laminates and finally the topsheet, a clear layer with the graphic printed on its underside. Into the heated press it goes, where pressure squeezes out any extra epoxy. The ski is then cleaned up and tuned. Once it’s cured, it’s ready for the slopes.

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