Mechanical pencil

A mechanical pencil (US English) or a propelling pencil (UK English) or a pen pencil (Indian English) is a pencil with a replaceable and mechanically extendable solid pigment core called a lead /ˈlɛd/. The lead is not bonded to the outer casing and can be extended as its point is worn away. The lead is actually made of graphite or a solid pigment.

Mechanical pencils are used to provide lines of constant thickness without sharpening in technical drawing and writing. They have also been used for fine-art drawing. They are also popular with students, since they do not have to be sharpened. Mechanical pencil lead is usually identical to a traditional HB (US #2) pencil.

Mechanical pencils were first used in the 18th century with many designs patented in the 19th and 20th centuries.

History

Detail of the first patent for a mechanical pencil of Sampson Mordan, 1822

Conrad Gesner described a leadholder pencil in 1565, but the lead had to be manually adjusted to sharpen it. The earliest extant example of a mechanical pencil was found aboard the wreckage of HMS Pandora, which sank in 1791.

The first patent for a refillable pencil with lead-propelling mechanism was issued to Sampson Mordan and John Isaac Hawkins in Britain in 1822. After buying out Hawkins' patent rights, Mordan entered into a business partnership with Gabriel Riddle from 1823 to 1837. The earliest Mordan pencils are thus hallmarked SMGR. After 1837, Sampson Mordan ended the partnership with Riddle and continued to manufacture pencils as "S.MORDAN & CO". His company continued to manufacture pencils and a wide range of silver objects until World War II, when the factory was bombed.

Between 1822 and 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 0.3, 0.5 and 0.7. Even 1.3 and 1.4 mm mechanisms were 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 Tokyo and Osaka made large orders. 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

A Pentel Sharp ratchet draughting pencil disassembled, showing three 0.5 mm graphite leads.

Mechanical pencils can be divided into two basic types: those that both hold the lead and actively propel it forward during use, and those that only hold the lead in position against gravity.

Ratchet-based pencils are a variant of the clutch pencil, 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.

In one type of ratchet-based pencil, shaking the pencil back and forth causes a weight inside the pencil to operate a mechanism in the cap. A button may be present. 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 released. A very modern type has a mechanical engine that twists the pencil lead 6 degrees counter clockwise every time the lead is pressed on to the paper to keep the lead 50% less broad than the common propelling mechanical pencils, resulting in uniform thickness of the lines written onto the paper. It was first developed by Mitsubishi Pencil Co.,LTD, and named Kuru Toga. Screw-based pencils advance the lead 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. Many of these have a locking mechanism one way to allow the lead to be pushed back into the pencil.

A clutch pencil (or leadholder) tends to use thicker leads (2–5.6 mm) and generally holds 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

A mechanical pencil by Caran d'Ache.

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

Mechanical pencil mechanisms use only a single lead diameter. Some pencils, such as the Pentel Function 357, place several mechanisms within the same housing, so as to offer a range of thicknesses (in this case three: 0.3, 0.5 and 0.7 mm). 1.00 mm leads also exist, but they are very rare. (See table below.)

Different sizes of lead diameters are available to accommodate various preferences and pencil builds, as shown in the table below. The most popular lead sizes are 0.5 mm and 0.7 mm, whose line widths allow for precise writing and drawing. There are also rare 0.2 mm leads and limited edition 0.1 mm leads (manufactured by Pentel).

Diameter (mm)	Uses
0.20	technical work
0.30	technical work
0.40	technical work
0.50	general writing, general technical work, beginner's technical work
0.70	general writing
0.90	students/general writing
1.00	rare, used in pre-1950 Parker pencils
1.18	older, used in pencils like the Yard-O-Led
1.30	Staedtler and Pentel (colour leads only for Pentel)
1.40	Faber-Castell e-Motion and the new Lamy ABC as well as some Stabilo children's pencils
2.00	drafting leadholders
3.15	non-drafting leadholders
5.60	non-drafting leadholders

Pencils with sub-millimeter leads can usually hold multiple leads at the same time, reducing the frequency of refills. One exception was the Pentel 350 E, possibly Pentel's first mechanical pencil, which could only hold a single stick of 0.5 mm lead. Refill leads can be bought in small tubes and inserted into the barrel as needed.

Pigments

As with non-mechanical pencils, the leads of 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 mm, 0.7 mm, or 2 mm) for their own products. Koh-i-Noor makes mechanical colored pencils with replaceable leads in 2.0, 3.15 and 5.6 mm sizes.

See also

• Technical drawing tools

Bibliography

• Deborah Crosby, Victorian Pencils: Tools to Jewels, Schiffer Publishing Ltd., Atglen, PA, 1998.
• Jonathan A. Veley, "The Catalogue of American Mechanical Pencils", Greyden Press, 2011.

External links

• Sharp's history of the mechanical pencil
• History and development of Keeran's and Hayakawa's pencil styles
• Leadholder Museum (History and Images of Leadholders)
• Pens-Bells – information and reviews
• Mechanical Pencil Museum Jonathan Veley's Mechanical Pencil Museum
• Sampson Mordan. First patent for a mechanical pencil