Months after I had discovered it, the materialization was near. Found on Vimeo through some random google search, while attempting to figure how to remove the cog from the loaner test Rohloff, was Aaron Lisco’s custom Rohloff wrench. It was a beautifully machined piece of aluminum that eliminates the worry about loosing purchase (tool grab) on the other OEM cog tool manufactured by Rohloff AG. This is of the utmost importance as extreme force is needed to remove a cog that has been tightened by thousands of miles of pedaling. These characteristics were achieved by creating a tool that can be sandwiched by the hubs skewer. All of this functionality and design only weighs in at about an ounce and a half.
Now I had to find a way to materialize this 3-D computer rendering into an actual object. I began by contacting some of the ME students who are members of the Cal Poly HPV(Human Powered Vehicle) club as well as techs in the student machine shops on campus. Despite being consumed by school and hundreds of hours of club work constructing their yearly competition vehicle, they reached out to me. After weeks of e-mailing, coordinating and materials purchasing, Chris Hunt and I set up a time to operate the machine at the end of his last day of class.
The Mustang ’60 machine shop was quiet in the wake of deadweek after a full quarter of fabricating on a limited shop schedule because of the departments inability to pay the shop techs to keep the shop open. Upon transferring the small aluminum work piece and ¼” endmill, Chris began to carefully clamp the work piece to the work table squaring it up a little bit at a time.
Once he was satisfied with the location of the piece he began to press buttons on the intimidating looking keyboard. He was using a bit called a Jem to aid the computer-controlled mill in knowing where the work piece was located. Chris was very precise in his setup of the machine since the tool is as wide as the workpiece (bar of aluminum) that it was to be made out of.
Before we ran the mill Chris showed me an animation of the milling sequence, stopping every once and awhile to manually adjust the code inserting an extra step to allow us to view the outline cut path before we had fully committed to removing metal. When the program was loaded onto the CNC Mill we watched the whiring endmill traverse the perimeter of the tool so that we could make sure it would not miss the metal stock completely. Once satisfied with the setup, we fired the coolant jets and began to cut.
It was incredible watching the mechanical arm find the exact cutting locations and layer by layer remove all of the unwanted metal. When the coolant had cleared there sat a perfectly outlined tool etched into metal flat bar. The tool itself was still connected to the bar by a thin foil of aluminum that stood between the mill and its own self-destruction. Thanks Chris for all the great work on this project.
After a quick clean up, I was left to break the tool free of its casing. Using cruder tools such as sheet metal sheers, pliers and some sand paper wrapped around a Sharpie, I began to liberate the tool of its extraneous metal. The process was slow, and the perforations surround by nothing but a thin webbing of 50 thousands of an inch, or as they say at the machine shop “thou”, thick. A punch and a hammer seem to be adequate at simply shearing the material away a couple of millimeters at a time around the perimeter of each perforation.
After several hours of metal removal with jeweler like precision the tool was complete. I choose not to punch out the reliefs in the handle for fear that I might damage the tool, and besides I think that the machined finish looks sexy. Now all I need is the modified chainwhip tool to ensure that I will be able to remove a worn cog anywhere in the world.