1. Determine the total number of teeth, radius to the inside of the teeth and radius to the inside of the teeth. (Determine if you have rounded or pointed teeth to your gears.) If you have rounded teeth add the rounded size outer diameter and subtract it from the inner diameter.)
2. Create cross hair construction lines to find the center point of the gear.
3. Draw two circles that correspond to the inside and outside radius of the gear teeth.
4. Draw a single line from the center point to of the gear to the outer edge of the outside circle.
5. Put the line created in the step above on a unique layer.
6. Lock the layer of the cross-hairs and circles.
7. Using the command ArrayPolar rotate twice the number of lines than teeth in the gear.
8. Lock the layer of arrayed lines.
9. On a unique layer draw one tooth of the gear between three of the lines. (For rounded teeth create three teeth and fillet the edges of the teeth.)
10. Trim the the three teeth to one tooth.
11. Lock all layers except the layer of the teeth.
12. Select all of the teeth and using the join tool make them a single line/curve.
12. Using the arraypolar command create the number of teeth in your gear.
13. Using the menu command Solid--> Extrude Planar Curve --> Straight Extrude the gear to the correct thickness/height.
14. Add holes, depressions, or other characteristics to your gears.