1. Sketch the profile for the screw and the wheel. As an example, we used these:
2. Convert them into solids with the PULL tool:
3. For the wheel/worm gear, the following profile is sketched onto a grid placed slightly above the tangent of the cylinder with larger radius. You may also use the spline tool to add more of a curve.
4. Use the 'project' tool to align these segments onto the curved surface.
5. Select this new surface patch and click on the 'move' tool. Drag the move handle to the center of the grid and tick the 'pattern' box under the tool options.
Now, drag the rotational handle along the z-axis (blue color) to replicate the surface patch 50 times along the circumference of the wheel. This will form the teeth of the wheel. You can select a lower count (25/30) to get a less dense teeth pattern (like the model at the top).
6. Using the Pull tool, either drag the teeth pattern outwards or inwards from the center of the wheel.
In this example, we drag inwards.
7. Go back to step 3 where we sketched the tooth profile. We use this as a reference to create a shape for the screw thread.
8. Use the CTRL key and move tool, copy this shape and align to the length cross-section of the cylindrical screw.
9. Switch to 3D mode and then using the PULL tool, revolve this shape as a left-handed helix along the length of the cylinder. Enter value of the pitch as the width of a tooth on the wheel.
10. With the screw and the wheel complete, feel free to assemble them according to your design requirements.