Associated Tooling

Why Make a drilling jig?

The last operations performed on the hangers are the drilling and tapping of the axle holes. The initial thought was to use the CNC to drill and tap these holes, however that would add two setups on a 3 axis CNC which would consume machine time and would eat into the companies pockets. Instead, a work holding fixture was created to enable an operator to accurately drill and tap the holes by hand on a drill press.

The hanger is placed into the fixture roadside away from the clamp so that the roadside bushing seat contacts the bushing seat locator. A clamp guide bushing is then inserted through the kingpin hole into the guide holes in the center of the bushing seat locators. The toggle clamp is then thrown, firmly and deterministically locating the hanger for drilling. Once one side of the hanger is drilled, the hanger is removed, rotated 180 degrees about the kingpin hole, and the above process is then repeated.

The fixture has been designed so that when the hanger is rotated to drill the other side, the initial hole lies in the same line of action as the second hole. The design theoretically worked well however there was flaw in its implementation. Due to wear of the end mill used to cut the slots in the datum fixture for the pivot, these slots came out slightly undersized. Additionally, the same end mill was used to cut the pivot, and by the time I had machined hangers to be used in the tool it was the last lab day of the quarter, which is when I discovered the geometric discrepancy caused by the tool wear. It was nearing the end of the day, and in a hasty attempt to remedy this issue, I skimmed some material off on a manual mill. Unfortunately on of the slots ended up roughly 20 thousandths of an inch too large.

This 20-thou deviation was enough to throw one of the axles out of alignment on the final pair of trucks that I made. To have prevented this error which resulted in both a faulty part and a messed up tool, what I should have done is thoroughly measured the tool after its production. Had I done that, I would have been able to stick a new end mill into the machine and run the operation again. By failing to perform proper metrology on my tool I cost myself not only time and money, but more importantly the opportunity to walk away with a flawless project.

Though this outcome was both personally and professionally disappointing I learned the importance of inspecting every part. I also learned the importance of frequently checking tools for wear or other damage to prevent mistakes from occurring in the first place. Although I was not able to produce the quality of parts I had set out to produce, this failure offered much more value to my knowledge than a perfect set of trucks ever could.