Trailer Hitch Rack Mount

I like to keep my car prepared for anything. I keep a toolbox in the back at all times with jumper cables, an impact wrench, a first aid kit, even a fire extinguisher. This level of preparation has saved me in the past if I get an unexpected flat tire or some other minor emergency, but it does come at the cost of having stuff roll around the back of my car. One day the sound of my trailer hitch adapter rolling around my trunk became too much of a nuisance so I decided to come up with an elegant and functional solution to secure the piece of hardware. I decided to take advantage of one of my empty cargo racks. One of them was occupied by my first aid kit and fire extinguisher, but the other rack was empty and ready to be utilized.

I made a prototype in CAD which held my specific trailer hitch mount using a correct constraint strategy to ensure that the piece would be held securely without being overconstrained. The design I chose constrains all axes of translation and rotation. The adapter can be inserted and removed using no tools only the hardware required for installing into the trailer hitch.

Final CAD

My third attempt at a 3d printed prototype succeeded and provided an appropriate fit to my trailer hitch to hold it securely while still granting sufficient clearance to easily install and remove it. Without access to any equipment besides a 3d printer. I ran the 3d printed version for a couple months knowing that soon enough a hot day would come along to melt my temporary plastic solution.

3d printed prototype

That day finally came in June when a hot day warped my 3d print beyond practical use. At that point I was back at school and had access to a HAAS CNC milling machine which I could use to make my design into a permanent solution. I adapted the design to make better use of a stronger but more expensive material (I went with 6061 aluminum) and I added some creature comforts like tapped holes instead of counterbores for bolt heads.

Beginning of adaptive clearing pass with a ballnose end mill

The finished product was manufactured without a hitch (get it?) and is still performing well for me to this day. This project also served as a good training exercise for CAM and prepared me to make many more parts in the 2023 Baja SAE build season. In the photo below, note the reduction of material especially on the ball side to reduce the cost and machining time while still maintaining full functionality. The final version has great fitment and doesn’t make noise as I drive thanks to the validation steps I took with cheaper 3D printed prototypes.

Finished Product