Drafting and Designing Equipment
Drafting and Designing Equipment
the instruments, attachments, and other equipment used to make mechanical drawings. The principal articles of drafting and designing equipment are a drawing board for arranging and securing the drawings, a stand on which the drawing board is mounted, a drafting machine, drawing instruments, and auxiliary equipment.
The drawing board has a flat surface whose dimensions exceed those of the drawing by 100–200 mm. Drawing boards are usually made of linden laths; plywood (for school drawing boards) with an oak or beech frame; glass; plastic; or chipboard with a plastic surface. Drawing boards made from a transparent material and equipped with a light fixture underneath facilitate tracing and copying. Boards made from combinations of materials are also used; one half is made from organic glass with scale grids and regulated illumination from beneath, and the other half is made of wood or laminated chipboard. Portable boards are 300 × 500 mm, designer’s boards are 1,000 × 1,350 mm, and boards for particularly large drawings are 1,350 × 5,000 mm. The drawings are secured to the board by tacks or tape.
A stand is used to hold the drawing board in a convenient position for work—at any angle and 300–700 mm above the floor. Fixed stands may have one or two columns. Single-column stands can be rotated 360° about the vertical axis. Stands for designer’s drawing boards have a system for balancing the board (for example, by means of weights or springs) or a device for raising, lowering, and turning the board (usually with a mechanical or hydraulic drive).
A drafting machine is a precision device that makes it possible to draw straight lines of a given length at any angle in the plane of the drawing board. Two types are used: the pantograph, which consists of a system of levers hinged together in the shape of a parallelogram, and the coordinate type, which has two mutually perpendicular bars along which carriages are moved. The parallelogram mechanism (in the first type) and one of the carriages (in the second) have protractor heads with two mutually perpendicular, scaled straightedges. The straightedges may have different scales and lengths; the horizontal one is usually 500 mm long, and the vertical 300 mm. The straightedges are made from metal-reinforced plastic or a thin-walled steel section. The protractor head provides an accuracy of up to 5’ (with continuous settings or detents for increments of 15°). The head has two scales for reading (positive and negative) and a device to shift the scales in order to construct projections at an angle. The machine has a lock mechanism to set the position of the head and turn it 90° from the plane of the board, attachments to align the straightedges, parallel rules for hatching, and lettering devices.
Drawing instruments consist of sets of marking and drawing compasses and outside calipers of various types and sizes, in addition to (when necessary) auxiliary attachments, ruling pens and holders, and the like. The range of radii inscribed with the various types of compasses is generally 0.5–300 mm or wider. Sets of drawing instruments also include cases for storing compasses, leads, and spare pen points, often made in the form of a screwdriver, point holder, or extension device. Brass buttons with a point and an indentation for the support leg of a compass are used to protect the surface of drawing boards and paper when inscribing concentric circles. Brass is used to make the most accurate instruments for critical work; less accurate instruments are made of steel.
A set of drawing instruments often includes devices for sharpening pencils and removing lines drawn by mistake. Leads, except those of calibrated thickness, are sharpened by manual or electric sharpeners. Pencil lines are removed from drawings with rubber erasers. For the correction of drawings executed in certain paste-like media that are absorbed deep into the paper, a white paste is used to cover up the unwanted elements of the drawing. The india and regular inks used in calibrated pens with reservoirs can be removed from a drawing with erasers that have a microporous structure; in the pores of the erasers is an india ink solvent, which dissolves the ink and removes it at the same time.
Auxiliary equipment is used to draw characters, letters, or numerals. Manual writing devices include various types of pencils, ball-point pens, soft-tip pens, and calibrated pens with ink reservoirs (in Russian, rapidografy). Mechanical pencils with graphite cores and graphite-containing pastes in metallic, calibrated tube holders are widely used; they do not need sharpening and allow one to draw lines 0.2–1 mm thick. Lines of varying thickness are also obtained with ball-point pens. Soft-tip pens produce lines of consistent width. They have cores made of glass fiber, polyamide (for example, kapron), or ceramic material. When drawings are made with india or special inks, calibrated pens with ink reservoirs are used; they draw lines 0.1–2.5 mm wide and are manufactured in seven or eight standard sizes.
Various types of rulers (including T-squares) and triangles are used in making mechanical drawings. Among the devices used to speed up drafting work are templates (for writing in inscriptions and standard designations and drawing standard parts), french curves (for drawing complex curved and connecting lines), and decals, which are small, dry, transferable illustrations of often-used fasteners, standardized circuits, and fixture representations. Mechanized means, such as typewriters, are also used to print letters, numerals, and standard symbols. The use of the templates, the simplified representation of often-used elements, and the pasting up of drawings from standard elements are other techniques designed to reduce the volume of drafting work.
The use of computer-controlled automated equipment improves the quality and increases the productivity of design work. Such equipment includes board– and roll-type graph-plotting devices, scanning and discrete-processing graphic copiers, and graphic displays. Drawings and other documents can be executed on paper, microfiche, or microfilm; the information they contain can also be converted into digital form and be recorded on machine information carriers, such as punched cards or magnetic tape, for subsequent computer processing. The use of automated equipment in drafting and design work speeds up the design process.
Drafting and designing equipment and supplementary fittings and devices are used in organizing the designer’s work position. The designer keeps the necessary reference works, templates, and a calculator at a writing desk used for making calculations. Drawings and auxiliary materials, calibrated pens, and other items are kept on a preparation table, which is usually set between the writing desk and the drawing board stand; drawing instruments and various reference materials are kept in the drawers of the table or in roll-out stands. Work positions equipped with a display and a graph-plotting device are usually combined into complexes for use by groups of designers working together.
REFERENCESAlferov, A. V. Mekhanizatsiia i avtomalizatsiia proektno-konstruktorskikh robot. Moscow, 1973.
Mekhanizatsiia inzhenerno-tekhnicheskogo i upravlencheskogo truda: Spravochnaia kniga. Edited by I. I. Kandaurov. Leningrad, 1973.
R. G. VARLAMOV