Mechanical pencil
The lead, often made of graphite, is not bonded to the outer casing, and the user can mechanically extend it as its point is worn away from use.
Mechanical pencils are used to provide lines of constant width, without need of sharpening, for tasks such as technical drawing as well as for clean looking writing.
[2] The earliest extant datable example of a mechanical pencil was found aboard the wreckage of HMS Pandora, which sank in 1791.
[3] 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.
His company continued to manufacture pencils and a wide range of silver objects until World War II, when the factory was bombed.
The first modern mechanical pencil was the Eversharp (originally "Ever Sharp"), invented by Charles R. Keeran who applied for the key patent in 1913.
[7] A pioneering mechanical pencil in Japan was invented in 1915 by Tokuji Hayakawa, a metalworker who had just finished his apprenticeship.
By 1924, Tokuji Hayakawa had turned his attention to the manufacture of radios, but his first invention was immortalized in the name of his new company: Sharp.
[8] Some present-day manufacturers are: Pentel, Pilot, Tombow, Uni-ball and Zebra of Japan; Faber-Castell, Lamy, Rotring and Staedtler of Germany; Koh-i-Noor Hardtmuth of the Czech Republic; Bic of France; Monami of South Korea; PaperMate and Parker of USA; Caran d'Ache of Switzerland and numerous Chinese as well as other Asian and European manufacturers.
A typical clutch pencil is activated by pressing the eraser cap on the top, to open the jaws inside the tip and allow the lead to freely drop through from the barrel (or back into it when retracting).
Because the lead falls out freely when the jaws are opened, its forward movement cannot be controlled except by external means.
Other designs use a precisely-fitted metal sleeve to guide and support the lead, and do not need a rubber retainer.
A button may be present on the top or side of the pencil, to allow the user to advance the lead manually when necessary.
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 design was first patented by Schmidt of Germany, and later developed by Mitsubishi Pencil Company of Japan, and named Kuru Toga under the Uni brand.
There exist protection mechanisms that prevent the lead from breaking (within certain limits) when excessive pressure is exerted while writing.
A mechanism employed in the DelGuard system by Zebra of Japan causes the lead sleeve to extend outward when excessive pressure is applied at an angle.
This allows the lead guide pipe to retract back into the pencil body, which will keep it protected in storage and during transit and makes it 'pocket-safe'.
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).
