Technical drawing

# Technical drawing ## Technical Drawing: Instruments used and sample drawing ### 1. Introduction Welcome to the exciting world of Technical Drawing! Technical drawing is a special way of drawing objects accurately and precisely. It's like a secret language used by engineers, architects, and designers to show exactly how something should be made or built. In this lesson, we will learn about the important tools used in technical drawing and how to use them to create accurate drawings. ### 2. Key Concepts #### What is Technical Drawing? Technical drawing is a type of drawing that provides very detailed and precise information about an object. It includes measurements, materials, and how different parts fit together. Its main purpose is to communicate design ideas clearly and without any confusion to people who will build or manufacture the object. #### Instruments Used in Technical Drawing To make accurate drawings, we need special tools. Here are some of the most common ones: * **Drawing Board:** This is a smooth, flat surface, usually made of wood or plastic, where you attach your drawing paper. It provides a stable base for accurate drawing. * **T-Square:** A T-square is a drafting tool with a head and a blade. The head slides along the edge of the drawing board, allowing you to draw perfectly horizontal lines. It also serves as a guide for your set squares to draw vertical and angled lines. * **Set Squares (Triangles):** These are triangular tools used for drawing precise angles and lines. The most common ones are: * **45-degree set square:** This has two 45-degree angles and one 90-degree angle. It's used for drawing lines at 45 degrees. * **30-60-degree set square:** This has angles of 30, 60, and 90 degrees. It's used for drawing lines at 30, 60, and 90 degrees. * **Pencils:** You will need special drawing pencils with different hardness levels. The hardness is shown by letters: * **H (Hard):** Used for light construction lines (e.g., 2H, H). * **HB (Hard Black):** A general-purpose pencil for outline drawing. * **B (Black/Soft):** Used for darker, bolder lines (e.g., B, 2B). * **Eraser:** Used to correct mistakes and remove unwanted lines without damaging the paper. * **Drawing Paper:** Special paper designed for technical drawing, often in standard sizes like A4 or A3. * **Drawing Clips/Masking Tape:** Used to secure your drawing paper firmly to the drawing board so it doesn't move while you are drawing. * **Protractor:** A semi-circular tool used for measuring and drawing angles accurately. * **Compass:** Used for drawing circles and arcs (parts of circles) of different sizes. * **Divider:** Similar to a compass but with two pointed ends. It's used for transferring measurements or dividing lines into equal parts. * **Scale Rule:** A ruler with different scales (e.g., 1:1, 1:2, 1:5, 1:10). It allows you to draw objects larger or smaller than their actual size while keeping the correct proportions. * **French Curves/Flexi-Curves:** Tools used for drawing smooth, irregular curves that cannot be drawn with a compass. #### Basic Drawing Techniques (Sample Drawing) Let's look at how to draw some basic shapes and lines accurately: * **Line Types:** Different lines tell different stories in technical drawing: * **Visible Lines:** Thick, dark, continuous lines that show the visible edges and outlines of an object. * **Construction Lines:** Very thin, light, continuous lines used as guides for drawing. They are usually erased later. * **Hidden Lines:** Medium thickness dashed lines that show edges or features that are not visible from the current view. * **Centre Lines:** Thin lines with a pattern of long dash, short dash, long dash. They indicate the center of circles, arcs, or symmetrical objects. * **How to Draw a Square/Rectangle:** 1. **Secure your paper:** Attach your drawing paper firmly to the drawing board using clips or tape. 2. **Draw a horizontal baseline:** Place your T-square against the left edge of the drawing board and draw a light horizontal line with your pencil. 3. **Draw vertical lines:** Place a set square (e.g., 90-degree edge) against the T-square. Draw vertical lines upwards from the ends of your baseline to the desired height. 4. **Complete the shape:** Slide the T-square up to the desired height and draw another horizontal line to connect the top ends of the vertical lines. You now have a rectangle or square. * **How to Draw a Circle:** 1. **Mark the center:** Lightly mark the exact center point where you want your circle to be. 2. **Set the compass radius:** Open your compass to the desired radius (distance from the center to the edge of the circle). For example, if you want a 60mm diameter circle, set the radius to 30mm. 3. **Draw the circle:** Place the compass point (needle) on the center mark and slowly rotate the compass to draw a smooth circle. * **How to Draw an Angle:** 1. **Draw a baseline:** Use your T-square to draw a straight horizontal line. This will be one side of your angle. 2. **Mark the vertex:** Choose a point on the baseline where the angle will begin (the corner). 3. **Position the protractor:** Place the center of the protractor exactly on the vertex point, making sure the baseline of the protractor aligns perfectly with your drawn baseline. 4. **Mark the angle:** Find the desired angle (e.g., 60 degrees) on the protractor scale and make a small mark on the paper. 5. **Draw the second line:** Remove the protractor and use a ruler to draw a straight line from the vertex to the mark you made. You have now drawn an accurate angle. ### 3. Vocabulary * **Technical Drawing:** A precise and detailed drawing used to convey information about an object's design and construction. * **Drawing Board:** A flat, smooth surface used as a base for technical drawing. * **T-Square:** A drawing instrument used to draw horizontal lines and to guide set squares. * **Set Square:** A triangular drawing instrument used for drawing vertical and angled lines. * **Protractor:** A tool used for measuring and drawing angles. * **Compass:** A tool used for drawing circles and arcs. * **Scale Rule:** A ruler with multiple scales used to draw objects at different proportions. * **Construction Line:** A light, thin line used as a guide during drawing, often erased later. * **Visible Line:** A thick, dark line showing the visible edges of an object. * **Hidden Line:** A dashed line showing features that are not visible from the current view. * **Centre Line:** A line made of alternating long and short dashes, indicating the center of a symmetrical feature or a circle. * **Radius:** The distance from the center of a circle to any point on its circumference. \( R \) or \( r \). * **Diameter:** The distance across a circle passing through its center. It is twice the radius. \( D = 2R \). ### 4. Examples **Example 1: Using the T-Square and Set Square** Imagine you need to draw a rectangular wall for a small building. You would use your T-square to draw the horizontal floor line. Then, you'd place your 90-degree set square against the T-square to draw the perfectly vertical wall lines upwards. Finally, you'd slide the T-square up to draw the horizontal roof line, creating a perfect rectangle. **Example 2: Drawing a Bolt** If you were to draw a simple bolt, you would use a compass to draw the circular head and the circular cross-section of the shaft. You would use your T-square and set squares to draw the straight sides of the shaft and any flat surfaces on the bolt head. ### 5. Exercises 1. Match the following instruments to their primary use: * T-Square * Compass * Protractor * Set Square * Drawing Board A. Drawing perfect circles and arcs. B. Measuring and drawing angles. C. Drawing horizontal, vertical, and angled lines. D. Providing a stable surface for drawing. E. Drawing parallel horizontal lines. 2. What is the main difference between a visible line and a hidden line? 3. List three different pencil hardness grades and explain when you would use each. 4. Using your T-square and a set square, draw a perfect square with sides of 60mm on your drawing paper. 5. Using a compass, draw a circle with a radius of 40mm. 6. Using a protractor and ruler, draw an angle of 75 degrees. ### 6. Assignment 1. On an A4 sheet of drawing paper, neatly draw the outline of a simple rectangular room with dimensions 100mm by 80mm. Inside the room, draw two dividing walls using visible lines. 2. Draw three different types of lines (visible, hidden, and centre lines) each 50mm long, clearly labeling them. 3. Draw an equilateral triangle (all sides and angles equal) using your T-square and set squares. Each side should be 70mm. 4. Practice drawing five different circles with varying radii (e.g., 20mm, 25mm, 30mm, 35mm, 40mm) on a single sheet of paper. ### 7. Summary In this lesson, we learned that technical drawing is a precise way of communicating design information. We explored the essential instruments like the drawing board, T-square, set squares, pencils, compass, and protractor, and understood their specific uses. We also practiced basic techniques for drawing accurate lines, squares, circles, and angles. Mastering these tools and techniques is fundamental to creating clear and effective technical drawings.