I've found that modeling a spur gear parametrically has been easier than usually easier than using a gear from Solidworks' readily available toolbox, and because it's so easy, I am going to show you how to do it for yourself. Feel free to follow along with the attached video.
I have attached the cheat sheet and the spur gear .SLDPRT for those of you who would like them for later use.
Step 1: The Tip Diameter (Using the Addendum)
For the equations above feel free to choose any value for number of teeth, pressure angle, and module. The values chosen for pressure angle and module in this tutorial are fairly common, and for a gear to mesh properly with another it must have the same pressure angle and module
Begin making three concentric circles and setting the center circle as a center line, or as reference geometry. Set the new reference circle as the reference diameter. The larger circle should have a distance between itself and the reference circle equal to the addendum, and the smaller circle should have a distance between itself and the reference circle equal to the dedendum. Exit the sketch and extrude the circles 10mm midplane.
Step 2: The Tooth Roots and Fillets (Using the Dedendum)
For this step please follow along in the video in the introduction, as there are too many constraints to explain in type.
This step covers the forming of the tooth cavities and the filleting of the vertices of the cavity.
Step 3: Final Steps
Now we are going to create a circular pattern of the cut and fillets that we made earlier. Make sure when creating the circular pattern you select both the fillets and the cut for the patterned features, and then the exterior of the cylinder the the rotational axis. Set the number of patterned items equal to how many teeth your gear is to have, and set the angle between the patterned items equal to 360/number of teeth.
Now that your gear has teeth add any additional features you need and send it to your slicing program for printing. for best results print from one of the circular faces of the gear, rather than the bottom up.