Mastering the Extend, Lengthen, and Join Commands in AutoCAD

Welcome back to the part of our AutoCAD Essentials for Mechanical Engineers blog series, we delve into some of the key commands that can drastically improve your efficiency when working on AutoCAD drawings. These include the extend, lengthen, and join commands, which are fundamental to creating precise technical drawings, especially when dealing with complex mechanical components. 

Let’s break down each command and explore how it applies to AutoCAD 2D drawings. 

 The Extend Command 

The extend command is used to elongate an object to a specified boundary. Think of it as an extension of the stretch command, but instead of performing a freeform stretch, you’re working with a hard boundary. This is especially useful in AutoCAD for mechanical engineers, where precision is critical. 

For example, if you have a line at an oblique angle that needs to intersect with another object, you can use the extend command to ensure it precisely meets the boundary. 

Here’s how to do it: 

• Draw a line at an angle. 
• Invoke the extend command by typing EX. 
• Select the boundary objects that the line should extend to. 
• Once the objects are selected, hover over the line to see it extend to the boundary. 

This method works for multiple objects at once, and you can use additional commands like fence or crossing to manage more complex selections. This is a great tool to keep in your AutoCAD essentials toolkit, especially when working on AutoCAD mechanical drawings. 

The Lengthen Command 

The lengthen command allows you to extend or shorten an object by a specific distance or percentage. This is useful when you need exact control over how much to alter an object’s size. 

To use the lengthen command: 

• Type LN to invoke the command. 
• Select the object you wish to extend or shorten. 
• You’ll be prompted to choose from several options: Delta, Percentage, Total, or Dynamic. 

For example, if a line is currently 110mm and you want to extend it by 50mm, you would choose the Delta option and enter 50mm. Alternatively, if you want to reduce it to 75% of its original size, use the Percentage option. These features are incredibly useful in AutoCAD for beginners, helping them work with exact measurements without hassle. 

The Join Command 

The join command is a highly efficient tool in AutoCAD when you want to merge two or more objects into one. Whether you’re working with linear or curvilinear objects, the join command can help create unified elements in your drawing. This is essential when working on mechanical AutoCAD 2D drawings, as it helps simplify the drawing by reducing the number of separate elements. 

To join two objects: 

• Select the Join command by typing J. 
• Select the objects you want to merge. 
• Press Enter, and the selected objects will become one. 

For example, if you have two lines on the same axis, the join command will merge them into one continuous line. You can also use it to join arcs or other curved elements, making it a vital tool when working with complex geometries in CAD for mechanical engineers. 

The Scale Command 

The scale command allows you to adjust the size of an object relative to a base point, either scaling it up or down. This is crucial when integrating components from different AutoCAD drawings or adjusting elements in a mechanical AutoCAD drawing to fit within specific design constraints. 

To use the scale command: 

• Type SC to invoke the command. 
• Select the base point for scaling. 
• Enter the scale factor or use the reference option if you need to scale an object to a particular length. 

For instance, if you want to scale an object to half its size, enter .5 as the scale factor. The reference option can be particularly helpful when scaling objects from other CAD programs that may not share the same dimensions. 

The Rotate Command 

In AutoCAD, the rotate command lets you change the orientation of an object by specifying an angle of rotation. This is particularly useful in mechanical design, where components often need to be aligned or rotated at specific angles. 

To rotate an object: 

• Type RO to invoke the command. 
• Select the object you want to rotate. 
• Specify the base point and the desired angle. 

For example, if you want to rotate a rectangle by 45°, simply enter the angle after selecting the base point. This can be combined with the copy option, which retains the original object while creating a rotated version. 

Practical Application: Drawing a Latch Plate 

To illustrate how these commands work together, let's apply them to a practical example. Suppose we are drawing a latch plate — a mechanical element that is bolted onto a surface and contains a slot for a latching element. 

Key dimensions include: 

• Four 5mm diameter holes. 
• A 12mm wide internal slot. 
• Overlapping circular holes with diameters of 20mm and 4mm. 
• Chamfered edges with angles varying from 15° to 135°. 
• External surfaces filleted with a radius of 5.6mm and internal fillets with a radius of 2.5mm. 

By using the rectangular, circle, and line options in AutoCAD, combined with commands like offset, trim, extend, and mirror, you can efficiently create this design. This method showcases the power of combining AutoCAD 2D drawing skills with knowledge of key commands. 

Conclusion 

Mastering commands like extend, lengthen, join, scale, and rotate is essential for anyone using AutoCAD for mechanical engineers. These commands not only streamline your workflow but also ensure precision and accuracy in your drawings, which are vital in mechanical engineering. 

Whether you are a beginner taking an AutoCAD crash course or a professional looking to refine your skills, understanding how to manipulate objects with these commands will help you create more efficient and precise AutoCAD mechanical drawings. 

For those looking to enhance their skills further, consider exploring an AutoCAD free certification course or an AutoCAD mechanical crash course to deepen your understanding of this powerful CAD software. 

Keep practicing these commands, and soon enough, you’ll be using them intuitively as part of your AutoCAD essentials training! 

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

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