How to use rack and pinion mate in onshape

Here’s a clear step-by-step guide on how to use rack and pinion mate in onshape(CAD Software).

How to Use Rack and Pinion Mate in Onshape

The Rack and Pinion Mate in Onshape creates a relationship between a rotating cylindrical part (pinion gear) and a translating linear part (rack), so that rotating the pinion moves the rack in a straight line — just like a real rack and pinion mechanism.

Step 1: Prepare Your Parts

Pinion Part: A cylindrical gear or shaft that will rotate.
Rack Part: A linear bar with teeth (or just a slider if you’re focusing on motion, not actual teeth).
Ensure both parts are fully modeled and inserted into an Assembly.

Step 2: Apply Primary Mates

Before adding the rack and pinion relationship, make sure:

The rack can slide linearly (use Slider Mate or Planar Mate to allow translation).
The pinion can rotate (use Revolute Mate or Cylindrical Mate to allow rotation).

Step 3: Add the Rack and Pinion Mate

In the Assembly toolbar, go to Mate Features → Rack and Pinion Mate.
Select:
- Cylindrical face (or circular edge) of the pinion.
- Linear edge or sketch line along the rack’s path of motion.
Enter the Pitch Circle Diameter (PCD) of the pinion gear — this defines the gear’s effective radius.
Choose the direction of motion (clockwise/counterclockwise).

Step 4: Test the Mechanism

Drag the pinion gear in the assembly.
The rack should move linearly in sync with the rotation.
If the direction is reversed, flip the direction setting in the mate options.

Step 5: Fine-Tune

Adjust the pitch circle diameter if the travel distance does not match your gear design.
Ensure no extra mates overconstrain the motion (it should move freely).

Tips

You don’t need detailed gear teeth for motion simulation — a simple cylinder (pinion) and rectangular bar (rack) with correct pitch diameter works.
Use Mate Connectors carefully so the axis of the pinion and the path of the rack are properly aligned.
You can later add gear teeth for visual accuracy, but they aren’t necessary for the mate to function.