Often abused and generally unappreciated, coordinate measuring machines (CMMs) are the underdog of the machining world. That’s because, unlike their metal-cutting cousins, CMMs don’t actually produce anything. No chips, no shiny machined parts, nothing but measurements and statistics. But remove the lowly CMM from any shop and you’ll be checking parts with height gauges and dial indicators, suffering an inspection backlog sure to make even the most patient shop owner hot under the collar. Simply put, CMMs deserve more respect.
A big part of that respect begins with a preventative maintenance program. Yet Gary Rockwell, director of aftermarket products for Michigan-based Nikon Metrology Inc., says this is one thing many shops forget. “There are basically two types of CMM—air bearing machines and those with mechanical bearings. Both require preventative maintenance.” Rockwell sayys most PM work involves cleaning the bearing surfaces, as well as the scales and feedback system. “I actually clean the entire machine if I can; the less dirt on the machine, the less likely it is you’ll contaminate any important surfaces.”
On air bearing machines, which comprise the lion’s share of CMMs today, cleanliness begins with the air supply. “Any kind of oil or vapour coming into the machine will clog the air bearings,” Rockwell says. “And moisture on the bearing ways attracts dirt, compounding the problem. But a supply of clean, dry air coming in provides an air curtain as it exits the bearings, helping to force dirt away.”