Mastering Rectangles, Polygons, and Polylines in AutoCAD

Welcome back to our AutoCAD Essentials for Mechanical Engineers series! This guide, we explored various tools and techniques that are essential for creating precise geometries in AutoCAD 2D and AutoCAD 3D designs. We’ll cover methods to draw rectangles, polygons, and polylines, as well as how to customize and manipulate these shapes for specific engineering purposes. 

Let’s dive in to recap the key concepts! 

Drawing a Rectangle in AutoCAD 

One of the basic but crucial shapes in AutoCAD is the rectangle. When working in AutoCAD for mechanical engineers, understanding how to control the dimensions and properties of rectangles can save time and ensure precision in your designs. 

Specifying Area and Dimensions 

Let’s say you need to draw a rectangle with an area of 120 mm². You can specify the area and let AutoCAD calculate the other dimension based on a given length. For example, if the length is 52 mm, AutoCAD will automatically calculate the width. The quick properties tool allows you to check the dimensions and ensure accuracy. 

• Length: 52 mm 
• Width: 2.3 mm (calculated based on area) 

If you need to directly specify the length and width: 

• Type RECTANGLE. 
• Enter the length (e.g., 52 mm) and width (e.g., 5 mm). 
• Place the rectangle on the drawing area. 

Rotating a Rectangle 

You can also rotate the rectangle to a specific angle. For example, setting an angle of 45° will rotate the entire rectangle, making it ideal for designs that require angular positioning. 

Creating Polygons: Inscribed and Circumscribed 

The polygon tool in AutoCAD is another essential for mechanical engineers, especially when dealing with hexagonal bolts or other multi-sided objects. You can create polygons either inscribed within or circumscribed around a circle. 

Steps to Draw a Polygon 

1. Invoke Polygon Command: Type POLYGON or select the tool from the ribbon. 

2. Specify Number of Sides: For example, you can create an octagon (8 sides). 

3. Choose Inscribed or Circumscribed: Decide whether the polygon should be inside or outside the circle. 

• Inscribed: The polygon fits within the circle. 
• Circumscribed: The polygon encloses the circle. 

For instance, if you create a polygon with a radius of 15 mm, the difference between inscribing and circumscribing becomes apparent. The inscribed polygon fits inside the circle, while the circumscribed one extends outside it. 

Drawing with Polylines 

Polylines are a powerful tool in AutoCAD because they allow you to combine lines and arcs seamlessly. This is especially useful for mechanical engineering drawings where complex shapes need to be drawn efficiently. 

Creating a Polyline 

• Type PLINE or select the polyline tool. 
• Begin drawing straight lines, arcs, or circles as needed. 
• You can switch between drawing straight lines and arcs by typing A for arcs, and the command will continue until you terminate it. 

Polylines are also beneficial because they combine multiple segments into one object, making it easier to modify, move, or replicate. 

Advanced Hands-On Exercise: Creating a Spacer with Hexagonal Nuts 

Now, let's put these tools into practice by drawing a spacer element with bolted hexagonal nuts in AutoCAD. 

Step-by-Step Guide 

1. Set Up Drawing Limits: For an A2 size paper, the height is 594 mm and the width is 420 mm. Ensure the model space is correctly defined by setting the limits. 
2. Define Units: Operate in millimeters with a precision of two decimal places. For angles, use degrees. 
3. Draw the Spacer
4. Start with a circle representing the outer diameter (150 mm). 
5. Draw the inner circle for the through-hole (90 mm). 
6. Draw the Hexagonal Nuts
7. Use the polygon tool to create hexagonal nuts (6 sides) inscribed within a circle of 15 mm diameter. 
8. Use the array command to replicate the nuts along a pitch circle diameter of 120 mm. 
9. Use polar arrays to create 8 instances of the nuts around the spacer. 

This exercise demonstrates the practical use of AutoCAD for mechanical engineers. You now have a spacer element with bolts, following standard mechanical drawing principles. 

Key Commands and Tools 

Drafting Settings 

This blog, we explored object snap and polar tracking commands, which are essential for precision in AutoCAD drawings. These tools allow you to quickly align objects, track angles, and snap to specific points, speeding up the drafting process. 

Dynamic Inputs 

We also looked at dynamic inputs, where you can switch between absolute and relative coordinates using symbols like the comma , and at @. This feature helps streamline your input process by providing prompts and tips directly on the screen. 

Undo and Redo Commands 

We discussed how to use the undo and redo commands effectively, allowing you to revert changes or redo actions, ensuring flexibility during design. 

Editing Commands 

Key editing tools like move, copy, mirror, and array commands were covered. These commands allow for efficient manipulation and replication of objects in your AutoCAD mechanical drawings. 

Conclusion 

In this guide, we’ve focused on fundamental tools like rectangles, polygons, and polylines, as well as core editing commands. By mastering these, you’ll be able to handle more complex drawings with precision, especially in mechanical engineering projects. 

As you move forward, practice these techniques in your own drawings. Whether you’re working on AutoCAD 2D or transitioning to AutoCAD 3D, these commands are vital to creating accurate and efficient designs. 

To reinforce your knowledge, explore additional training options such as an AutoCAD essentials course or a free AutoCAD certification course to further your skills. Good luck, and stay tuned for more exciting lessons in our AutoCAD for mechanical engineers series! 

This blog is part of our ongoing AutoCAD Design Series. If you missed the previous posts, check them out here.  

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