Basic Tech, JSS 1 Week: 3
Topic: Drawing Instruments and Materials
Technical drawing is a universal language used for communication among technical people.
These are engineers, technicians, designers, builders, etc. It is a language expressed in terms of graphic illustrations which convey the idea of shape, size and other features of engineering components used in the manufacturing and construction industries. We study drawing so that we can draw objects for other people to see and understand what we have in mind without talking to us or asking questions. It is therefore important that we learn the language of drawing. To do this, we start with the descriptions of instruments and materials that are used, and later we learn how to use them to produce drawings and how to take good care of them.
Instruments and Materials for Technical Drawing
A good and accurate drawing can only be made through constant practice with the aid of drawing instruments and materials. Below is a list of instruments and materials for technical drawing.
Drawing, Tee-square, Set-squares (300 x 600 and 450), Protractor, Compasses, Dividers, Drawing paper clips, Scale rules, Metric rules, French curve, Template, Lettering set, Sharpener, Drawing pencils, Drawing paper, Adhesive, Erase, Emery cloth, Glass paper.
Drawing board is the wooden platform on which the drawing paper is placed before the drawing commences The two main types are discussed below:
Full imperial size: This is 812 x 585mm (millimeters) in size. These types are usually left at the studio by the draughtsman. It has a tee-square (or already parallel bar to it) which can slide from the top of the table to bottom; the board can also be inclined to the desired position
Half imperial (585 x 452mm) size: This is the most useful it it portable and ideal for the much simpler work that students will be involved in. Ideal drawing bards are made of medium-hard, ever-grained hard wood or fine-grained plywood (12-18mm thick) both with slotted battens on the underside to keep it flat.
Tee-square is used for drawing horizontal lines and it also supports set –squares during drawings. The ideal tee-square is the one that is the same size as with the drawing board. The tee-square is placed on the drawing board with the stock at the left had edge of the board. A suitable tee-square is made of mahogany with the square edge lined with a hard wearing wood such as ebony for durability.
Tee-square can also be made of an opaque plastic stock and transparent plastic blade.
Drawing pencils are of different grades. There are two types of pencil:
- Soft pencils: These are soft and black. These include grade pencils. They are hard pencils. These include H grade pencils, such as H, 2H, 3H, 4H to 8H pencils.
Uses of Pencils in Technical Drawings
- For general drawing: 3H or 2H grade pencils are ideal
- For lettering or freehand sketching: Use H or HBgrade pencils sharpened to a ‘conical point’.
- For technical or engineering drawing: Use 2H or 3H grade pencils sharpened to a ‘chisel point’
A piece of fine emery cloth or No. O glass paper or a pencil sharpener would be necessary to keep the points sharp for working to fine limits.
Also we have thin lead mechanical pencil (refill) which requires no pencil sharpening . It is also available in different grades.
Set of Drawing Instruments
There are various brands of sets of drawing instruments. A complete set should contain the following:
A compass: used for drawing circles and arcs
A divider: used for transferring measurement from the metric rule to the drawing.
Ink lining pen attachment for compass.
An election compass is ideal, with needle points and adjustment devices, knee joints and extension bars.
Set-squares are used to draw vertical or diagonal lines. They can also be paired up for specific angle drawing. Set-square play an important role in technical ,engineering or geometrical drawing. Acrylic (plastics ) set-squares are of great value, and highly satisfactory with careful use as the bevel edges are helpful for inking in. Teachers can make of wooden ones on the chalkboard.
Drawing Paper Clips or Adhesive Tapes
Drawing papers are best held on the boards with the aid of clips or adhesive tape. The use of pins or cello-tape should be discouraged because it also causes the distortion of centre lines while cello tapes deface the finishing on the paper.
Protractor: The protractor is used for measuring and marking out angles. An ideal protractor is made of acrylic materials with divisions ranging from half a degree through 900 to 1800.
Scales rules are used to produce reduced or enlarged sizes of objects. They are usually triangular in shape and have three edges. Generally, each edge of the scale rule is graduated, and each scale designation is marked on the rule. The use of a scale rule is vital, as most linear sizes are not possible on paper. Therefore, with a scale rule, we can enlarge or reduce the size of an object on paper. A metric rule is used for measuring straight lines. It is usually mad e of steel, wood or plastic. It has two straight edges graduated in centimeters, millimeters and inches. A typical ruler is 30cm long.
French curves are used for drawing various types of curves. Ideal French curves are made of acrylic material in which possible curvatures are incorporated. Another type consists of a flexible bar which can be physically bent to suit various curves (known as flex curve).
This is the paper on which the drawing is produced. Creamy white paper is ideal for drawing. The sizes vary in relation to the size of the drawing board usually from quarter to full imperial. Suitable metric sizes are A2, A3 and A4.
Drawing paper sizes are listed below:
A0 = 841mm x 1189mm
A1 = 594mm x 841mm
A2 = 420mm x 594mm
A3 = 297mm x 420mm
A4 = 210mm x 297mm
Other Drawing Papers
In addition to the normal creamy-white drawing paper, they are:
(a) Tracing paper and (b) transport cloth-baked drawing paper.
- Tracing paper: This is a transparent paper used for original drawing which are later printed on normal drawing paper. Tracing papers are reference papers for original copies.
- Transparent cloth-baked drawing paper: This is used almost the same way as the tracing. Valuable documents are usually drawn on cloth-baked papers and they are ‘originals’ as against copies for which normal tracing papers are intended. This type of paper is usually used by surveyors.
There are various types of erasers and they are generally called rubbers. A good eraser must erase cleanly without picking or tearing the surface of the paper.
These are available in various shapes, such as geometrical shapes (e.g. squares, circles, polygons, quadrilaterals, etc.) or shapes of architectural designs (e.g. floor plan, plumbing, furniture, landscape, etc.) or letters and alphabets.
These are instruments used by the draughtsman or the designer to draw various types of letters and alphabets. These include lettering machine, latter guide, template, pen, scriber, etc.
Care of Drawing Instruments
Just as we need to take of ourselves, our clothing, houses and other property, so also do our drawing instruments need good care in order to prolong their service life and for safety reasons. Therefore, these precautions should be observed in respect of the following instruments:
- Do not use pins for fastening your paper to the board, use tapes or clips
- Do not use blade or knife to cut something on the surface of your drawing board.
- Always cover the surface with cardboard or thick paper.
- Keep the drawing board in a safe place when not in use.
- Never use the tee-square as a walking stick or as a cane.
- Do not use pen knife or blade along the edge of the tee-square.
- Always hang your tee-square when not in use.
- Always keep your tee-square clean
Set-square, Scale Rules, Protractor and French Curves
- Do not use any sharp object such as razor blade or knife on their edges
- Keep them away from fire
- Always keep them in a safe place immediately after us to prevent breakage.
Pair of Compasses or Dividers
- Do not sit or step on compasses
- When not in use, keep them away in a safe container.
- Never use compasses or dividers as paper holders.
- Do not use their needle points to punch holes.
- All other instruments should be kept in their packets after use.
- A cupboard should be made available for complete storage of the drawing boards and all other instruments.
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