Porsche Boxter & Cayman "hidden hitch" adapter for utility trailer

thingiverse

Posted are the models and dimensions to create a "hidden hitch" mount for Porsche Cayman and Boxters. This is reverse engineered from images posted on the planet-9 site and measurements taken from the self-locking ball mount made by www.etrailer.com I took measurements from 2" hitch components at Home Depot to verify the tolerances of the square receiver hole. It was also handy to have a spare bumper channel to measure its features. Along the way I 3D printed a full size sample in PLA to check fit and clearances, before finding a shop to cut this out of a block of 6061 aluminum. For those that have never turned a wrench or touched a hacksaw... ***This design is for steel or aluminum.*** 3D printed plastic is fine for testing fit and concept only ! The STL serves CNC users who have access to software like CAMWorks that can read features & surfaces from "dumb-solids," while the dimensioned prints serve those who have access to a manual milling machine or those that know how to enter a design into the controller of a CNC milling machine. **** This is an at your own risk design. Towing a trailer can be dangerous and you must assume all responsibility for manufacturing, installation, and use of the design. The set of parts created for a single cayman worked and has been proven road-worthy on many trips to the track, but the installation continues to be inspected before and after every use to make sure it's safe. If you can't assume risk for this design, then don't use it. **** http://www.planet-9.com/reviews/cayman-cosmetic-mods/p285-behind-the-box-solutions-hidden-hitch.html It would have been impossible to realize this without the information provided in the planet-9 posting. It took several revisions to eliminate challenging machining geometries and the process caused several gut check moments on cost to machine, feasibility, and safety. Along the way I found an off-the-shelf less fancy version in steel that uses a more traditional ball adapter that is currently available... it can be found at: https://picclick.ca/SporTTows-Stealth-Hidden-Hitch-Porsche-911-272908016681.html#&gid=1&pid=3 Very late in the process we found a manual for the original design that was sold by "Behind the Box Solutions" and it included several pages of legalese disclaimers. It is believed that the liability and profitability of this design and devices similar are significant issues. In our case we chose to recreate the no longer available "Behind the Box Solutions" because it was the cleanest design. Buying pre-made would have been preferred, but that wasn't an option. My version of it is surely different. But it works and installs the same using the notes from Planet-9. So if you've gotta have this style adapter, here are some details that will help. * the two mounting bolts are 3/8"-16tpi * the holes in the models account for the root or tap diameter in the part that goes inside the bumper channel and the major diameter of the clearance holes required by the outer block. Your machinist should modify the hole diameters as needed for the hardware you select. * metric would have been nicer, but SAE is just easier to source in grade-8. * Locktite and lock-washers were used for obvious reasons and the bolt heads were marked with paint following installation to allow for routine inspection to make sure the assembly remains tight before and after each use. * ***these parts were cut from 6061 aluminum*** * the most important features in the machining of this are that the 2" square receiver holes are concentric along with the pair of bolt holes * the originals shown in the planet-9 posting are beautiful. For cost, I chose to drop all, except for essential chamfers and forego anodizing. So, my models aren't as pretty to look at or handle, but they work.... and once installed, it's unlikely a sharp edge will hurt you. * the trailer we chose was aluminum for weight and corrosion resistance. It is an Ultra-Tow 40"x48" trailer from Northern Freight and has been upgraded with a form cut aluminum diamond plate bed and many mods to accommodate tire and tool box mounting. * if you chose the correct etrailer self-locking ball mount your trailer will be level when ready to roll. I think the planet-9 posting talks about hitch selection. * The 12" tires provided with these trailers are not rated for highway speeds, but other Porsche owners with these small trailers report they've had no problems at highway speeds. Keeping the trailer and load light likely helps keep these wimpy tires from being a major issue. Also be sure to travel with a spare wheel ready to bolt on. [[[ UPDATE - recently found 12" trailer tire/wheel combo rated for 81 mph ]]] **** This is an at your own risk design. Towing a trailer can be dangerous and you must assume all responsibility for manufacturing, installation, and use of the design. The set of parts created for a single cayman worked and has been proven road-worthy on several trips to the track, but the installation continues to be inspected before and after every use to make sure it's safe. If you can't assume risk for this design, then don't use it. ****