Understanding a gear and its geometry

A gear is a rotating mechanical part, made to transform the speed, torque and direction of a motion. Usually they have a circular shape and teeth to intermesh with other gears.

To check if two gears can be meshed together, you need the gear module. Divide the amount of teeth by each gear’s radius to calculate the module. Only gears with the same module may be intermeshed.

M = n / r # Module = Teeth / radius

The second most important parameter for 3D-printing gears is the gear’s clearance. If two gears are intermeshed, this is the distance between the gear’s base circle (the gear without teeth) and the other gears teeth. The so-called working-depth is the gear’s teeth height plus the gear’s clearance.

The gear-ratio (calculable by dividing the gear’s radii) between two gears of the same module determines the amount by which the gear’s rotational speed is reduced or increased, which decreases the gear’s force.

Also good to know: the angle of pressure is the angle at which the gear’s teeth meet. For more details on gear terminology, see the gear-nomenclature Wikipedia article.

Modeling gears in Blender

After understanding gears, you could just go ahead and model one yourself. However, for reasons of efficiency, I went looking for automatic gear-generators.

After trying out a few, I ended up using the great Blender Addon GearGenMaster by Sergey Drachev (view on GitHub or download from here).

After installing the Addon, you will be able to find the generator in the menu under Add > Mesh > GearGenMaster. There you can set the required gear parameters, which then will be used to generate a gear mesh.

Printing the gears

  1. Use Blenders export stl feature to export your gear models to .stl files.

  2. Import the stl in your slicer software (I commonly use Cura).

  3. Adjust the slicer settings: I like to print gears with lots of brim to make the gear stick, two outer walls and 40% triangular infill, leaving the bottom of the gear open.

  4. It is usually smart to redrill the holes contained in your gears, so you get your tolerances right.

Simulating gears in Blender

You can simulate gear movement in Blender by adding constraints to the gear meshes you generated:

  1. Use rotation limits to only allow rotation around the gear’s rotational axes.
  2. Use the copy-rotation constraint on gears acted upon by others. Remember to set the invert flag, which makes the gears rotate in opposite directions. For gears with a different gear ratio, set the influence parameter of the constraint equal to the gear ratio between the two gears (example: 10 teeth / 20 teeth = 0.5)

After setting the constraints right, you can rotate all gears by rotating just a single one. After that, you can use keyframes (linear interpolation mode) to make the gears move by themselves.

I hope this post was useful to you! If it was, make sure to follow my Twitter @finnmglas. If I got something wrong, reach out to me : )

- Finn M Glas, 2021-05-12 12:41:04 GMT+2