MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
I loaded the original STL file into 123D Design (could have used Tinkercad) and used Smart Scale to increase the height of the hair spring in the z-direction by 6 mm. I then inserted a block on top of the hub, moved it down 6 mm, and used the combine feature to subtract the cube from the hair spring hub to delete the unwanted 6 mm section of the hub. You can do the same thing in Tinkercad.