It is made of ultra-hard high-carbon steel which can cut stone, since pencil leads are made of a mixture of graphite and various types of clay, some of which are often used as abrasives. The steel used in KUM blades has a carbon content of 62 hrc., more than ball bearings (55 hrc.), for example, or high-quality knives.
The blade is sharp.
Each blade is razor-sharp. A felt sharpening wheel (similar to leather) is used as the last step in the automatic sharpening process. Note: stainless steel cannot be used because it cannot be sharpened that much.
The blade is held absolutely immovable. Otherwise, it would not cut at all.
A screw holds the blade onto the sharpener’s body, even on the cheapest KUM sharpener. If the blade comes the slightest bit loose, the sharpener is completely disabled. A screw holds much better than the rivet used by some other manufacturers. The screw is one of the (few) visible signs of a good sharpener.
The blade is curved, not flat. Acting like a spring, it exerts constant upward pressure on the screw, which keeps the screw from loosening. Other manufacturers do not make curved blades.
The pencil is held with the right precision for the right cut.
Precision metal sharpener body: it is made of magnesium alloy. Fine tolerances are needed by a sharpener in order to hold and shape a pencil point properly. Magnesium is hard enough to be worked with a milling machine at these tolerances. Some competitors use aluminum, which is too soft and malleable for this type of milling, although much cheaper than magnesium. Other competitors use a die-cast metal body, which cannot be made with as much precision.
Precision plastic sharpener body: the injection mould is so accurate that it even allows for shrinkage of the plastic when it is ejected from the mould and cools.
In order to reduce wobble while turning the pencil, the sharpening hole is prolonged by an extra sleeve just forward of the inner cone. While the pencil is turning, that sleeve holds the outer pencil case, adding to the support provided by the cone-shaped part of the hole. As a result, the pencil remains perpendicular at all times. If the pencil wobbles, the graphite tip meanders even more than the wood casing, according to the mechanics of leverage. Yet graphite is brittle, and tends to break off when not treated with great care.
The pencil is easier to turn.
The sharpener’s blade is curved, not flat. As it is cutting the pencil, it weaves slightly up and down, dynamically adapting to the fibrous structure of the wood instead of ripping straight through it. The cutting friction is reduced, and therefore the pencil is easier to turn. This happens because the blade, made of carbon steel, is tempered and therefore flexible; its curved shape causes it to act like a spring pressing up against the screw that holds it in place. The tension thus created gives the blade its dynamic characteristics. KUM calls it the “Dynamic Torsion Action™”.
The cone-shaped inner surface of the sharpening hole is evenly rilled, reducing friction. This is particularly visible in our metal sharpener: there are tiny, even rills in the hole.
[for KUM Models #202, #S20A, #220A only] The pencil point is longer.
The sharpener blade is set at a narrower angle which produces a longer, sharper, and finer pencil point, which does not have to be sharpened as frequently.
Every sharpener blade is measured automatically during sharpening.
Every sharpener blade edge is inspected for sharpness before assembly.
Every sharpener blade is engraved with the KUM logo.
The sharpener’s blade lasts longer.
The blade is made of high-carbon steel, which is very hard (see above), lasting for thousands of sharpenings on normal pencils. N.B.: constant sharpening of pencils grade 3H and harder does require replacing the blade from time to time.
Rust protection of blade: high-carbon steel normally rusts quite easily, so three elaborate operations are used to protect every KUM blade, 1) polishing, 2) ultra-sonic cleaning, 3) coating with oil. This protection lasts for years except in warm climates with high relative humidity, where minute rust dots can form after six months. A stainless steel blade cannot be used in a sharpener because it cannot be sharpened enough. Rust does not affect the performance of a sharpener which is constantly used, since the sharpening action keeps the cutting edge clean.
The body of the sharpener lasts longer.
Polished magnesium body of metal sharpeners: the polished surface resists corrosion. It also gives the sharpener a cleaner and shinier appearance, and a brighter metal coloring. Special machinery is used in the polishing process.
The sharpener’s blade can be replaced, since it is screw-mounted. Some KUM sharpeners include spare blades. Spares blades are also available in convenient cases.
KUM Environmental manufacturing processes
All manufacturing and waste disposal activities comply with stringent requirements.
KUM packaging complies with the German “Green Dot” cardboard recycling program.
Non-toxic coloring granulates are used in manufacturing all plastic KUM components.
A new dry-painting process now produces KUM colored metal sharpeners. Once anodized, the new coating eliminates the use of a very toxic chemical product.
New ultra-sonic blade cleaning and blade coating machines use almost no toxic compounds.
Critical work areas in the factory have air filtering equipment for the well-being of the employees.
The KUM company policy: “We make everything ourselves”.
In-house design and machining of plastic injection molds: this allows absolute control over the dimensions of critical places such the “blade bed” and the cone-shaped hole of plastic sharpeners.
In-house design and construction of all automatic and semi-automatic milling and assembly machines: this ensures that all metal and wooden products measure up to KUM specifications.
In-house manufacture of all the parts of KUM products, except for the screw holding down the sharpener blade, ensures that all parts fit together correctly.