I will be showing you how to draw a 3d gear easily in this Illustrator tutorial. To make things more interesting, I will be using opacity mask to show through the wireframe of the gear. After this tutorial you will have a better understanding on drawing gears and 3D extrude tool in Adobe Illustrator.
1. Create the gear shape
Let’s star by turning on our Ruler by pressing Ctrl/Command+R. Drag 2 lines from the ruler to crate a center point. Now select you Circle Tool and press Alt/Option+Shift and drag from the center point to draw a circle.
Select the Star Tool. Click and drag front the center point to create a basic star. Without releasing your mouse, press Arrow Up key to increase the number of points. Hold Ctrl/Command and drag to adjust the radius until you get the shape below. Now select the circle and star shape and go to Window>Pathfinder and hold Alt/Option and click Add to shape area. This will create a sun flare effect as shown below.
Draw a new circle from the center point. This will define the outer edge of our gear. Now select both the sun flare and our circle and hold Alt/Option and select Intersect shape area.
Finally, draw a small circle in the middle. Next select both shapes and hold Alt/Option and choose Subtract from shape area to punch a hole in the middle. Our gear shape is finally out!
2. 3D Extrude
Select your gear shape and go Effect>3D>Extrude & Bevel. Select Plastic Shading for the Surface and move the spotlight on the sphere until you see something you like. Click OK to confirm.
3. Create the wireframe effect
Make a duplicate of the 3D gear shape by pressing Ctrl/Command+C and Ctrl/Command+F to paste it in front. Go to layers palette and hide the new pasted gear. Select the gear and go Window>Appearance to to open up your Appearance Palette. Double click 3D Extrude & Bevel to edit the options. Now select Wireframe for Surface.
Now unhide our grey gear from the Layers Palette. Next draw a square and fill it with a gradient from white to black with our Gradient Tool. The black will mask away the shape whereas the white areas will show through. Now select both the grey gear and the gradient and open up your Transparency Palette. Choose Make Opacity Mask to fade away the black areas.
This is our final gear. To make changes to the mask, select the gradient mask in the Transparency Palette. Then go to the gear and click and drag to change gradient angle.