If this is something of interest or something you do a lot, please follow the steps below:
- Firstly create your Part, complete with Slot, then select the Axis tool from the Work Features panel on the Model TAB of the Ribbon.
- Next, right click in the workspace somewhere and select Create Plane from the flyout menu.
- Select the Faces as shown below to give a Midplane along the Slot.
- Then right click in the workspace somewhere and select Create Plane from the flyout menu.
- This time instead of using Faces, select the Three Midpoints to create a plane as shown below.
- After this the Axis will be created and placed in the correct position on the model, you should also see that the new planes are consumed by the Axis and visibility is turned off.