Quality Magazine

Case Study: Air Gages Validate Spindle Interface Components

February 25, 2010
Stotz MRG air column displays all values of surface finish, taper angle and straightness. Source: Advanced Machine & Engineering


Advanced Machine and Engineering (AME, Rockford, IL) has been a customer of Stotz USA LLC (Freeport, IL) for a long time. Today, these two market leaders maintain a great working relationship, for all the right reasons.

AME demands the highest level of quality in their machining and finishing departments and Stotz air gaging systems facilitate the accomplishment of that goal, every day, according to AME service manager Greg Hobbs. “Air gaging is the only technology we’ve found that’s accurate enough to check the machine tooling and especially the spindle tapers we produce here. In the past, we’d use hard gages and we still use them, but only for certain OD (outside diameter) checks. We’d blue up the tapers, insert them, give them a good twist and do our inspections, but there was way too much inconsistency. Today, with sophisticated HSK tooling, this method is too hit or miss to be reliable. Air gaging provides dead stops on the test stand and the documentation is unbeatable for validation on the straightness, surface finish and taper angles. Plus, the Stotz system allows us to upload all the data on every part, so we have our favorite word-documentation-for every part we produce.”

Hobbs also comments on the user-friendliness of the Stotz air column. When the program is first input into the column for a part in the AME grinding department, for example, the Stotz column essentially becomes a programmable logic controller, providing hard data via the Ethernet connections to the host database. In this manner, every parameter of every part is documented and recorded. In a classic example of the law of unintended consequences, this process is not only used on the parts run, it also is used for calibrating the AME machines, in a predictive maintenance function.

At AME, various testing of machined spindle interface and other components is performed both at the machines in the grinding department, in a temperature-controlled 72 F environment, plus in the company’s totally environment-controlled in-house testing department, supervised by the company’s director of quality, Brad Patterson. He confirmed Hobbs’ observation that numerous other technologies have been investigated over the years for quality checking at AME and that air gaging has been found to be the best and most reliable for this company’s applications, particularly inside diameter (ID) dimensions and configuration.

At AME, air gaging has been found to be reliable for the company’s applications, particularly inside diameter dimensions and configuration. Source: Advanced Machine & Engineering

Patterson also observes, “The sophistication of the Stotz air column is unmatched in the industry. We get all the data required and we get it in exactly the fashion needed to support our customers. Repeatable results and elimination of error occur every time. Plus, the set-up is much faster than on our laser mics, which can’t be used for ID measurement.”

Patterson further notes that the replacement of the bluing technique, one he termed a “black art,” with air gaging has brought and keeps AME up to the most current industry standards for quality evaluation.

THE STOTZ AIR COLUMN

The typical Stotz air column found here is the Model MSG, with four pneumatic channels or 10 LVDT channels operating simultaneously, pneumatic length measuring, user-specific programming up to 18 programs per column, full statistical analysis and full data transfer capability within the host network. All information is fed into the AME host computer by serial number, so any job can be quickly retrieved, while historical records on any part produced can be easily called up for evaluation, deviation claims or to dovetail with a customer’s internal quality protocols.

Typically, as AME’s Grinding Supervisor Sam Schubert explains, the finished product will rest for 24 hours of soaking, allowing the diameters to normalize. Though statistically predictable for most metal materials, thermal expansion can cause off-normal readings to occur. For checking certain bearing journals or spindle shafts, snap gages are set to accommodate size measurements down to the 20 millionths (0.00002 inch) range. The acceptable diameter tolerances for most AME products measured are in the one- to two-tenths (0.0001-0.0002 inch) range.

In cases where new masters are made for setting control values, those values are preset offline and programmed into the air column’s software, according to Hobbs. Stotz typically performs this function for the customer in a remote manner over the Internet, through a proprietary IP address.

Among the many products finished in this grinding department are CAT/ISO 40 taper spindles, HSK test arbors, HSK grind quills and HSK steep taper milling tools. Often, older and worn spindle shafts are reverse engineered by AME for retrofits and remanufacturing. Even in these cases, air gaging is used to evaluate the finish process on the ID taper, as this technology is easily adapted to such applications, according to AME personnel.

At AME, various testing of machined spindle interface and other components is performed both at the machines in the grinding department and at the in-house testing department. Source: Advanced Machine & Engineering

Schubert expands on the use of Stotz air gaging at AME.

“We have a full and very expensive inventory of hard gages with state-of-the-art indicators attached. But the air gages can do so much more. We use them for set-up on the grinding machines and they save us hours, every week. When you run the number of jobs we do here, that translates into substantial, additional work product and therefore more revenue for the company. In terms of reliability, some of the Stotz air gages we run here have been at AME since we began using the technology, nearly 10 years ago now.” Schubert also notes the air gaging set-ups on the grinders dramatically reduce the time to first part in his department’s operation.

On one major spindle shaft project for an Asian machine tool builder, who was looking for a local source of supply in America, Schubert notes, AME was confronted with an unusually large quantity run, where tool degradation during the run would normally impact the production at some point. After an initial batch was produced, the machine builder claimed that everything but the taper was satisfactory. Surprised by this claim, AME checked all the documentation and determined that the customer’s test unit was actually out of spec, in a case where the error was repeated consistently and thus overlooked. In that instance, the AME products were deemed better than perfect.

Schubert cites a useful analogy here. “The documentation we can produce from the air gaging procedure is like a birth certificate on every unit we make. All our spindle shafts for customers, for example, can be viewed as a series of genetically identical twins to each other and we’re providing the documentation of their DNA.”

As evidence of their commitment to this technology, Schubert notes that AME is now purchasing air gaging fixtures for all new customer applications. This quality spindle interface manufacturer aims to “keep breathing easy” in their process and product validation, as a result.

Stotz USA LLC

(815) 297-1805

www.stotz-usa.com

Benefits

  • Incorporating air gages with grinding machines help save set up time by saving rework.
  • Information is fed into the AME host computer by serial number, so any job can be quickly retrieved.
  • Air gaging provides dead stops on the test stand and the documentation is unbeatable for validation on the straightness.