3D AutoCAD Tutorial: Create a 3D piston

When I first started to learn CAD a few years back, I had a major problem with my learning process. I couldn’t find any exercise material. I searched and searched but couldn’t find anything useful. I decided to create the 101 CAD Exercises book to help others speed up their learning process and make it more hands-on and fun. If you want more exercises like this, you can get them hereexercises are 2D and 3D drawings without instructions so that they are not specific to AutoCAD.)

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In this tutorial, you will learn how to create a piston using 3D geometry in AutoCAD. To do this you will use the 2D drafting and annotations and the 3D features. I assume that you are already a bit familiar with the basic 2D drawing commands such as LINE, CIRCLE, TRIM, etc. The final model should look something like this in 3D.

Here are the 2D drawings:

Remember that using gridmode (F9) and snapmode (F7) can be helpful between drawing tasks. For this exercise, I’ve been using AutoCAD 2017 but it will work with previous versions as well as other CAD software. Your commands and shortcuts might differ with other versions, though. The dimensions that are used in this exercise are originally metric but since it’s all proportional you can use the same values but with imperial units instead. I’ve decided to keep the measurements unitless for this exact reason.

1. Start a new drawing in AutoCAD.
2. Draw a circle with a diameter of 60 and place its center on the origin (0,0).
3. Draw a horizontal line that starts at the origin and a length of 23. This line will be used as a reference length for the next step.

 4. Draw a rectangle using the RECTANG command as shown on the right side of the image below, using the endpoint of the line as a guide to place the rectangle. The dimensions of the rectangle don’t need to be exact but they must exceed the circle perimeter as we use it as a cutter. Then mirror the rectangle using the start point of the line (or the center of the circle) for the mirror line. Remember to erase the reference line that you used to create the rectangle.

5.Now draw a concentric smaller circle with a diameter of 52. Also, draw a vertical line 19 units to the right of the center of the circles as shown below and mirror it. As with the rectangles, the lines need to exceed the circle perimeter.

6.Now use the TRIM command and use the vertical lines as edges to trim the inner circle. Resize the 2 vertical lines so that they end at the top and bottom arcs. Then use the JOIN command to make the following shape in the center.

7. Click the gear (Workspace Switching) icon on the bottom right of the screen and choose 3D Basics instead of Drafting and Annotation. Also choose a 3D viewpoint so you aren’t looking at plan view.

8. Now use the EXTRUDE command to extrude the shapes to make a 3D model. The Z dimensions (shown below) are 40 units for the rectangles, 44 units for the central shape,  and100 units for the circle. This image is using the X-ray visual style.

    9. Now start the SUBTRACT command and subtract every shape from the main cylinder. Remember that first you must select the main cylinder, press Enter and then select the objects you want to subtract from it. You might need to change your viewpoint or visual style, especially to subtract the central shape. Now you should have a model looking like this:

   10.Now you should go back to the 2D Drawing and Annotation and return to a top 3D view such as SE Isometric if necessary. Draw a concentric circle with a diameter of 52 and a rectangle (using the RECTANG command) with a height of 7.5 and one of its sides on the x-axis as shown in the image. The length of the rectangle should exceed the cylinder diameter, which is 60.

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