The best business relationships allow everyone involved to win. A case in point involves Gerhardt Gear, which recently teamed up with Process Equipment Co. for the solution to a problem that ended up expanding its capabilities.
Double flank roll-testers (DFR) have been around for decades as quick and efficient frontline production inspection tools. As with most “quick tests,” however, there are tradeoffs between fast and complete data. While a DFR does offer an accurate summary of deviations—“Total Composite Variation,” for example—it doesn’t allow the operator to determine which single errors caused the deviation. Furthermore, if the summary of deviations is within tolerance it’s assumed that the single errors are also within tolerance, which is precisely what caused a quality problem for Gerhardt Gear and its customer, a major aerospace component manufacturer, whose actuators were experiencing gear-related failures. Gears were inspected by both Gerhardt Gear and its customer, and both appeared to be within specification. Even though the DFR testing gave the gears the “green light,” some of the assembled actuators were noisy, while others simply wouldn’t function at all.
John Kim, Gerhardt’s quality manager, turned to a CNC gear measurement system. Unlike the DFR that was being used by Gerhardt and its customer, this system generates data about specific gear features and compares output results using multiple gear standards simultaneously. The operator controls or selects the format of the analysis reports generated, choosing for example to plot profile, helix, index, pitch, and tooth thickness along with standard analyzed parameters and accuracy class all on one page. Gearing standards such as AGMA, DIN, ISO, JIS or user-defined tolerances may be incorporated into the inspection data by the operator. Data acquisition algorithms can also provide true, error-compensated 3-D measurements on some CNC gear measurement systems.
Gerhardt’s fine pitch spur gears were CNC inspected for index, helix (lead), profile, and tooth thickness. The test revealed that the root cause was a pinion gear, provided by a new third party vendor. The pinion gear had a tooth thickness deviation that exceeded specifications by 0.002”—an extremely significant amount in the final gear assembly. The CNC data also indicated that this issue was exacerbated by an improperly sharpened hob at Gerhardt, which was reflected by another gear’s profile. For reference purposes a known good gear was also inspected, showing a more desirable profile and tooth thickness.
Within weeks of resolving the gear inspection issue Gerhardt Gear took delivery of a new CNC gear measurement system from PECo. Says Mitch Gerhardt, president, “Would you believe our customer is now sending the gears they manufacture to us for inspection on our CNC gear checker?”
The bottom line is that when gear and gear cutting tool manufacturers want precise and accurate information to monitor and control their gear manufacturing process, and when gear users want to document the quality of the gears going into their end products, the data from CNC gear inspection systems are a cut above DFR. Look for a case study in an upcoming issue of Gear Solutions. To learn more about PECo call (937) 667-7105, send e-mail to info@peco-us.com, or go online to [www.gearinspection.com]. Contact Gerhardt Gear at (800) 893-4024 or [www.gerhardtgear.com].
