How to Draw a Simple Machine Cog in AutoCAD (Beginner Level)

Objective:

In this tutorial, we’ll walk you through the steps to draw a simple machine cog (gear) in AutoCAD. By the end, you’ll have a basic understanding of creating gears with a pitch circle, teeth, and a central hole using simple AutoCAD tools.

1. Preparing Your Workspace

Before we start drawing the cog, it’s important to ensure your AutoCAD environment is set up correctly.

Step 1: Set Units

Open AutoCAD and create a new drawing.
Type UNITS in the command line and press Enter.
In the “Drawing Units” dialog box, select the desired units (e.g., millimeters, inches) for your drawing and click OK.

Step 2: Set Drawing Scale

Make sure your drawing scale is set to a proper size for the cog you want to create. For this beginner tutorial, you can use a simple scale.
Use the ZOOM command to adjust your view if necessary, ensuring you can see the entire drawing space.

2. Drawing the Pitch Circle

The pitch circle defines the size of the gear and is a key part of the cog’s geometry.

Step 1: Use the Circle Command

Type CIRCLE in the command line and press Enter.
Click to place the center point of your circle. This is where the cog’s center will be located.
Type the diameter of the circle (e.g., 50mm or 2 inches) and press Enter. This circle will be your pitch circle, which serves as the reference for the size of the gear.

3. Drawing the Teeth

We’ll draw one tooth and then replicate it around the pitch circle to form the cog.

Step 1: Draw a Single Tooth

Select the LINE command to draw the base of the cog’s tooth. For a basic cog, this could be a straight line.
Use the ARC command to draw the top of the tooth. It should be a simple curve that extends slightly above and below the pitch circle. You can create the arc using two points: one at the base and one above the pitch circle.
Alternatively, you can use a simple triangular shape if you prefer not to use curves for the tooth.

Step 2: Position the Tooth Around the Pitch Circle

Once you’ve created a single tooth, use the ROTATE command to rotate it into position.
To do this, select the tooth and type ROTATE in the command line. Specify the base point (the center of the circle) and then type in the angle of rotation (for example, 30° to start positioning it around the circle).

Step 3: Create the Tooth Array

Type ARRAY in the command line to replicate the tooth around the pitch circle.
Select Polar Array from the options.
In the “Array” dialog, set the number of items (e.g., 12 for a 12-tooth gear) and specify the angle between each item (for example, 360° ÷ 12 = 30°).
Press Enter to complete the array, and you’ll have a cog with evenly spaced teeth.

4. Adding the Center Hole

Your cog will need a central hole for the shaft. We can add that next.

Step 1: Draw the Center Hole

Use the CIRCLE command again to create a smaller circle at the center of your gear. This will be the hole where the shaft goes through.
Click on the center of the pitch circle to align the new circle with the cog’s center.
Type the desired diameter for the center hole (e.g., 10mm or 0.5 inches) and press Enter.

5. Refining the Cog Shape

Now we can clean up and refine the cog’s shape.

Step 1: Trim Extra Lines

Type TRIM in the command line to remove unnecessary lines that extend beyond the cog or teeth.
Select the lines to trim and press Enter. Trim away any segments where the teeth meet the pitch circle or where the arc extends past the necessary areas.

Step 2: Clean Up the Drawing

Use the ERASE command to delete any extra construction lines or unwanted segments that are no longer needed in your drawing.
Make sure the cog looks neat and clean with only the essential parts remaining: the pitch circle, teeth, and center hole.

6. Dimensioning the Cog

Dimensioning ensures the cog is accurately represented with its measurements.

Step 1: Add Dimensions

To add dimensions, type DIMLINEAR or DIMALIGNED in the command line and press Enter.
Click the two points you want to dimension (e.g., the diameter of the pitch circle or the distance across the center hole).
Place the dimension on the drawing, ensuring it’s clear and easy to read.

You can also dimension the number of teeth or other relevant features of the cog.

7. Final Adjustments and Save

Now that your cog is ready, let’s make a final review and save the drawing.

Step 1: Review Your Drawing

Zoom in and out of your drawing to make sure everything looks correct.
Check that all the teeth are evenly spaced, the center hole is properly sized, and the cog is symmetrical.

Step 2: Save the Drawing

Type SAVE in the command line or click the save icon at the top of AutoCAD.
Name your drawing and choose a location to save the file as a .dwg file for later use.

Conclusion:

Congratulations! You’ve just created a simple machine cog in AutoCAD. By following these basic steps—drawing the pitch circle, adding the teeth, creating a central hole, trimming, dimensioning, and saving—you’ve learned how to create a cog suitable for mechanical design.

This tutorial covered:

Essential AutoCAD commands like CIRCLE, LINE, ARRAY, TRIM, and DIM.
Basic concepts such as the pitch circle, tooth profiles, and the center hole.
How to refine and clean up your drawing.

With this basic cog, you now have a solid foundation to start designing more complex mechanical parts in AutoCAD. Happy drafting!

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