A mechanical pencil is a writing implement or art medium in which the solid marking core (usually graphite based and called lead, but coloured pigments and other solid substances are also used) is not bonded to the outer casing, and is designed such that the core is to be extended as its point is worn away. Mechanical pencils are known by many alternative names, some of the most common alternatives being lead pencil, propelling pencil, automatic pencil, drafting pencil, technical pencil, clicky pencil, clutch pencil, leadholder and pacer.
Mechanical pencils are often designed and used to provide lines of constant thickness without requiring sharpening, making them well suited to applications like technical drawing and writing.
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History
The mechanical pencil was invented in Britain in 1822 by Sampson Mordan[1] and Gabriel Riddle. Earliest Mordan pencils are thus hallmarked SMGR. Sampson Mordan continued manufacturing pencils and a wide range of silver objects until World War 2, when the factory was bombed.
Between 1822 to 1874, more than 160 patents were registered pertaining to a variety of improvements to mechanical pencils. The first spring-loaded mechanical pencil was patented in 1877 and a twist-feed mechanism was developed in 1895. The 0.9 mm lead was introduced in 1938, and later it was followed by 0.7, 0.5, 0.3. Even a 1.4 mm mechanism was available, and 0.4 and 0.2 versions are now produced.
The mechanical pencil became successful in Japan with some improvements in 1915 by Tokuji Hayakawa, a metal worker who had just finished his apprenticeship. It was introduced as the Ever-Ready Sharp Pencil. Success was not immediate, since the metal shaft—essential for the pencil's long life—was unfamiliar to users. The Ever-Sharp began selling in huge numbers, however, after a company from Yokohama made a large order. Later Tokuji Hayakawa's company got its name from that pencil: Sharp.
At nearly the same time, in America, Charles R. Keeran was developing a similar pencil that would be the precursor of most of today's pencils. Keeran's design was ratchet-based, whereas Hayakawa's was screw-based. These two development histories are often combined into one.
Mechanism types
Mechanical pencils can be divided into two basic types: those that both hold the lead and actively propel it forward in small increments during use, and those that only hold the lead in position against gravity.
Propelling pencil
Most mechanical pencils use small sub-millimeter leads and have an internal mechanism that propels the lead forward from a holding chamber inside the barrel. There are a number of different mechanism types:
- Ratchet-based pencils, in which the lead is held in place by two or three small jaws inside a ring at the tip. The jaws are controlled by a button on the end or the side of the pencil. When the button is pushed, the jaws move forward and separate, allowing the lead to advance. When the button is released and the jaws retract, the "lead retainer" (a small rubber device inside the tip) keeps the lead in place, prevents the lead from either falling freely outward or riding back up into the barrel until the jaws recover their grip.
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- A variation of the ratchet-based pencil, in which shaking the pencil back and forth causes a weight inside the pencil to operate a mechanism in the cap. A button may be present.
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- Another variation advances the lead automatically. In this design, the lead is advanced by a ratchet but only prevented from going back into the pencil, just held from falling by a small amount of friction. The nib is a spring-loaded collar that, when depressed as the lead is worn away, pulls out more when pressure is next released.
- Screw-based pencils, in which the lead is advanced by twisting a screw, which moves a slider down the barrel of the pencil. This was the most common type in the earlier part of the twentieth century.
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- Screw-based pencils in which the lead is advanced by direct friction with the screw.
- Twist-based pencils, in which the lead advances upon twisting the head of the pencil. Many of these have a locking mechanism one way to allow the lead to be pushed back into the pencil.
Clutch pencil
A clutch pencil (or leadholder) tends to use thicker leads (2–4 mm). Most hold only one piece of lead at a time.
A typical clutch pencil is activated by pressing the eraser cap to open the jaws inside the tip, allowing the lead to freely drop through from the barrel (or into it when retracting). Because the lead falls freely when the jaws are opened, its forward movement cannot be controlled except by externally halting its progress. This can be easily done by keeping the tip of the pencil a few millimeters above a work surface or the palm of one's hand.
Some clutch pencils do have mechanisms which incrementally advance the lead, such as the Alvin Tech-Matic leadholder, but are not normally considered to be in the same category as most pencils with propellant mechanisms.
Lead variations
Compared to standard pencils, mechanical pencils have a smaller range of marking types. Nevertheless, numerous variations exist. Most mechanical pencils can be refilled, but some inexpensive models are meant to be disposable and discarded when empty.
Diameter
Any given mechanical pencil can use only one lead diameter unless specifically contructed otherwise, such as the Pentel Function 357.
Different sizes of lead diameters are available to accommodate various preferences and pencil builds: 0.3mm, 0.5mm, 0.7mm, 0.9mm, and 2mm, among others. The most popular lead sizes are 0.5mm and 0.7mm, whose line widths allow for precise writing and drawing.
Pencils with sub-millimeter leads can usually hold multiple leads at the same time, reducing the frequency of refills. Refill leads can be bought in small tubes and inserted into the barrel as needed.
Pigments
As with non-mechanical pencils, the leads of non-mechanical pencils are available in a range of graphite/binder ratios, depending on the user's desired balance between darkness and durability.
Mechanical pencils with colored leads are relatively rare, but do exist. Crayola's "Twistable" product line includes two different types of colored pencils (erasable and non-erasable) with mechanical feed mechanisms, but does not offer refill leads. Several non-US companies such as Pentel, Pilot, and uni-ball currently manufacture colored refill leads in a limited range of diameters (0.5, 0.7mm, or 2mm) for their own products.
Footnotes
- ^ "History of Leadholders". Leadholders.com. 2008-01-04. http://www.leadholder.com/main-history.html. Retrieved 2008-02-27.
Further reading
- Deborah Crosby, Victorian Pencils: Tools to Jewels, Schiffer Publishing Ltd., Atglen, PA, 1998.
External links
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Wikimedia Commons has media related to: Mechanical Pencil |
- Sharp's history of the mechanical pencil
- History and development of Keeran's and Hayakawa's pencil styles
- Dave's Mechanical Pencils (Blog about mechanical pencils. Includes reviews.)
- Leadholder Museum (History and Images of Leadholders)
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