Drawing tutorial on gears and splined shafts.
Creating Illustrator vector line art in of a toothed gear in perspective.
All Tutorial Text & Images - Copyright © 2011 KHI, Inc.
Learning to draw a toothed gear is a basic skill for the beginner to intermediate technical illustrator or automotive artist. In this tutorial our subject matter will be a basic multi-toothed gear that would be found in machinery or automotive components, as shown in Fig. 1. We will start out by creating a simple cross grid Fig. 2 on it's own layer in Adobe Illustrator. The horizontal and vertical lines should be equal in length so that their center-points intersect. Lock this layer containing your grid. Next we will create a set of circles on a second layer using the Illustrator "Ellipse Tool" (E). To create the circles we will click in the center point of our grid and while holding the Option > Shift keys we will drag the cursor outward (Fig. 3). This will constrain the Ellipse Tool to a perfect circle.
Technical Note: In Adobe Illustrator when you hold the Option and Shift keys simultaneously while the Ellipse tool is activated the cursor changes form a simple cross to a cross within a circle (Fig. 6). Note: The following hardware and software was used in this tutorial: Apple Mac Pro, a Wacom Intuos 6x8 drawing tablet and Adobe Illustrator CS-CS5 or CorelDRAW vector drawing software.
Once we have finished our series of three (1 inner and 2 outer) circles we will begin to construct the teeth (Fig. 4). Our gear will ultimately have 40 teeth; therefore each quarter will have ten teeth (or twenty divisions). Working within the two outer circles we will create one tooth set (Fig 4 in black). Select all 3 paths of the tooth and group them together using the Object>Group in the menu bar or the Command>Group keyboard commands.
Using the Selection tool (solid arrow) select the first tooth and using both the Command and Option keys (cursor becomes double arrow) hit the "Nudge" or "Arrow" key once to the left. This will "Copy and Paste" a duplicate of your selection. Use the "Nudge" or "Arrow" key again to move it back to the right, placing it directly over the original. Rotate the tooth, using the blue cross-grid center-point as the rotational axis. You will notice that when you select the tooth, the "Origin" point is not in the center on our blue cross-grid. Click on the Origin Point and drag it to the grid center. Repeat the Copy & Paste process until all ten teeth in the upper left quarter are complete (Fig. 5).
Technical Note: If you leave the Rotate tool active while you Copy & Paste with the method above, the "Origin" center point will stay in the same location. This will speed up the process.
Next you will select all ten teeth and group them together. Copy and Paste as before. While this grouping is still selected, activate the Rotate tool. You will notice that the selection's "Origin" point is no longer in the center on our blue cross-grid. Again, click the origin point and drag it to the grid center. Rotate it downward while holding the Shift key to constrain it to a 45º move (Fig. 6). This will place the duplicate in the lower left corner completing half of the gear.
The next step will be to select both sets of ten teeth and group them together using Command>G (Fig. 7). Using our Copy and Past method from before, duplicate the selection and re-position the Origin point to the center of the blue grid. Using the Shift key to constrain the rotation, rotate the selection 180º as shown in Fig. 8. The completed gear face is shown to the right in Fig. 9.
We are now ready to distort the gear into perspective. Make sure that all of the teeth on both the left and right hemispheres of the gear are grouped together separately (Fig. 9). Unlock all paths and/or layers that remain locked. Drag the cursor across the image using the Selection Tool (V) to activate all paths (Fig. 10). Using the Selection Tool (V) or the Free Transform Tool (E), begin to compress the grouping vertically (Fig. 11). For this demonstration I have arbitrarily chosen a 30º ellipse ratio (1:2). The amount of distortion will be determined by the perspective and angle of view that the gear will ultimately be placed in.
Next we will use the Selection Tool (V) to activate the left half of the gear (Fig. 13). Make sure that all of the teeth are in one grouping. Drag the selection to the left using the Command>Option keys to duplicate the selection to the new location (Fig. 14). When you are finished, your illustration should look something like Fig. 15.
The next step will be to eliminate parts of the teeth from our background gear surface on the left. These lines will not be visible in the final art and only serve as a distraction. In Fig. 16 we are removing the back side of each gear tooth using the "Direct Selection Tool" (A). When you use this tool it will not activate the other paths in your grouping. When you are finished it should look like Fig. 17.
We are now ready to make our horizontal lines which will define the edges of the teeth. Make a new top layer and lock all underlying layers. Using the Pen tool, make a horizontal line that touches the left and right gear face (Fig. 18). This line will define the back side of a tooth. Using the Selection Tool (V), duplicate the line to each new position (back side of teeth) by holding the Command>Option keys while dragging the line downward. Once we have duplicated all of these lines on the top half of the gear we will select them and group them together using Command>G (Fig. 19).
Technical Note: It is helpful to use a different color for each active layer. This way, each grouping can be distinguished by its unique layer color. Double click on the layer in the layers palette to reset its preferences.
The next step will be to add the front edges of the teeth (Fig. 20) and the inner corners of the teeth (Fig. 21). Once we have finished all of the horizontal lines on the top half of the gear we will cut any lines that are behind the teeth (Fig. 22) using the Scissors Tool (C).
Varying Line Weights to Add Clarity
Using the Scissors Tool (C), we will cut the small sections of the rear, or trailing edge of the teeth that will help form the outline of the gear (Fig. 23).
Now we will start the process of varying the line weights to increase the readability of the illustration. Using the Direct Selection Tool (A), we will activate all of the Paths that form the gear's outline, and we will increase the thickness of those Paths by approximately 300% to 400% (Fig. 24). Any lines that form the back edge of the teeth but are INSIDE of the image will be thickened by approximately 200% (Fig. 25). This will result in a final illustration with four line-weights. In order of thickness they are: 1. Center line grid (0.05), 2. Fine interior lines (0.15), 3. Bold interior lines (0.35), 4. Outline of outermost edge (0.5). Technical Note: For additional information on controlling line weights and line quality go to the "Controlling Line Weights" tutorial.
Continue the process of varying the line weights on the backside of the gear (Fig. 26, 27) using the same technique as before. Add a line to define the back side of the center hole (Fig. 28) by duplicating the ellipse and cutting it in the appropriate location.
Once we have completed the finishing touches on all of the line art on the upper half of the gear we will drag across all paths to activate them and duplicate them by Command>Option dragging them downward (Fig. 29). Use the shift key to constrain the vertical movement. When the duplicated selection is in the correct location we will use the Object>Transform>Reflect dialogue box (Fig. 30) to flip it vertically (see technical note below).
The final step will be to drag your cursor across all visible paths and reset the "Bounding Box" using the Object>Transform>Reset Bounding Box command located in the menu bar. This step will reorient the Bounding Box to an upright position. With the entire selection grouped together (Command>G) you may now rotate the gear into its final position, orientation and size.
Technical Note: For some mysterious reason, earlier versions Illustrator CS require that you use the "Horizontal" command to flip an object vertically, and the "Vertical" command to flip an object horizontally. This anomaly is counterintuitive and may have been fixed in newer versions of Illustrator.
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