Blender Gears

I've been using gears for a couple of different projects.

My first foray into gears using Blender, was using the Add Mesh: Extra Objects plug-in. It opens up another "base" object in the Add Mesh > Gears > Gear options. It creates a gear without the faces connecting the inside of the center hole (a non-manifold model). It's easy enough to create these faces - alt-shift each inside ring, the bridge the edge loops (through Control-E for the edge menu, then Bridge Edge Loops, or spacebar-find Bridge Edge Loops).

Breaking it down

• Teeth is...teeth - the distance from the inside ring to the outside tooth tip is Base+Dedendum+Addendum
• Radius is the distance from the middle of a tooth, to the opposing side's middle tooth
• Width is the z-axis height
• Base is the inside of the ring to the outside of the ring
• Dedendum - the distance from the "middle" of a tooth, to the outside ring (increasing it, also shrinks the hole in the center)
• Addendum is the tip of the tooth, distance is figured again from the middle of the tooth to the tip
• Pressure angle is going to the slant of the tips of each tooth - anywhere from 0 degrees (square), to a maximum of 45 degrees (if your addendum is a larger value than your overall size, you'll need to reduce the pressure angle to avoid bad topology)
• Skewness is used for helical and herringbone gears - also known as a helix angle
• Conical angle has one end shrink to a cone - 45 degrees leads to a tip, where 0 is no cone, and 90 is flat (practical uses - 0 to 45)
• Crown makes a crown by elevating the tips and mid-points of each tooth - a measurement of the z-axis difference between the base of a tooth to the connected top of tooth (not a hypotenuse, which would be longer)

Woodgears

That's just how to lay out the gear, once you get your gear designed! I used this perfectly fine option from a site called Woodgears...he does a lot of great woodworking, and the gear tool is useful.

Otvinta's Instant Gear

My current gear-making assistant is Otvinta's Instant Gear. Their branding is "A collection of tutorials & resources for 3D modeling and 3D printing enthusiasts". The useful part, is how it generates a python script to create the gears.

You can then go into a Text Editor window in Blender (usually on the 3D View, lower left hand corner), click on the "+ New" button, to create a new text data block...paste that code, and the press the "Run Script" button. You have the outside outline of two gears, both preset as meshes (back in the 3D View).