1. Field of the Invention
This invention relates generally to mechanical pencils and in particular to mechanical pencils composed of a relatively few, simple inexpensive components readily adaptable to automatic assembly specifically for sale as a disposable writing instrument.
2. Description of the Prior Art
Previous designs of mechanical pencils that employed a helical coil rotatable inside a hollow barrel have either utilized split tubes surrounding the lead, or pushers which are disposed in the interior of the coil or split tube. Such prior pushers had radially extending projections which engaged the coil or barrel. These constructions necessitated threading the pusher into the coil or split tube to the proper position at assembly and therefore required the design of relatively complex and expensive machinery to accomplish the assembly of the various components.
Other types of pusher which engaged the coil about its turns were constrained by a separate guide means positioned within the barrel of the writing instrument. Here it was necessary to physically interconnect the pusher with the guide means as well as interconnecting the pusher with the coil, all of which entailed complex and expensive structures and methods of assembly.
Examples of such prior art are disclosed in U.S. Pat. Nos. 966,712 to C. A. Smith, 1,539,468 to Cook et al., 2,866,438 to Schischkow and 3,630,628 to Roman.
Accordingly, it is the object of the present invention to provide a mechanical pencil employing relatively few components, each of which is inexpensive and readily assembled by simple machines.
More specifically, it is the object of this invention to provide a mechanical pencil of such simplicity of structure, minimum number of parts, adaptability for automatic assembly and low cost of manufacture as to permit optional discarding of the pencil after the initial lead has been consumed, thereby eliminating the necessity of the user keeping a supply of spare refill leads and undergoing the sometimes tedious process of replacing the refill leads in the pencil with the attendant possibility of lead breakage during this process. The mechanical pencil of the present invention by its simplicity and low cost of manufacture hence is competitive with other disposable writing instruments.