Three-M invested in some of the most accurate, state-of-the-art milling machines to handle the new Clipper project. “These are some of the best milling machines in the USA, but they still are not accurate enough to hold the required tolerances on these parts. We can’t just machine the part to the print right off the milling machine,” states Michael Medwid. True position tolerances on these larger parts are about 25 microns. These new parts, typically made of cast iron, are rough-machined, undersized as three separate castings, assembled together and sent through in-process inspection, making sure screw holes are lined up, then re-machined to print as separate castings and assembled one last time for final inspection. In-process inspection is performed on every 10th part with 100 percent final inspection. The casting would warp out of shape if this process wasn’t followed
In 2010, two employees from ZF Industries visited Three-M to review their capabilities to produce gearbox housing prototypes. ZF Industries already inspects with three ZEISS CMMs in their Greenville facility so they were familiar with the systems. “After two hours they called their boss and said to quit looking because they had found their new supplier,” says Medwid. “Our ZEISS MMZ-G machine was the main reason we got that business,” claims Medwid.