McNeal Tool Company of Cedar Rapids, Iowa, a wholly owned subsidiary of聽Mid Iowa Tools, Inc., specializes in the sales and support of precision metrology instruments and services.聽 This includes provision of gage calibration services to a national manufacturer of window and door products that are sold into residential and commercial markets.
According to Wayne Schneider, McNeal Tool Field Engineer, 鈥淢any of the customer鈥檚 products include wood and extruded or roll-formed materials processed to length using tenoners, molder/profilers, or saws.聽 The length of these pieces can measure from around 90鈥� to 140鈥� or more, with tolerances typically kept to within 卤 0.002鈥�.
To help keep machining processes centered on nominal values, the customer utilizes an SPC measurement routine that includes periodic use of long,聽single-axis measuring tables specifically designed to verify accuracy of long workpieces.
The measuring tables are about 12鈥� wide, up to 140鈥� long, and equipped with聽digital readouts.聽 Accuracy of the measuring table set-ups is regularly verified utilizing an 鈥渁ssembly鈥� of the longest available, standard gage blocks 鈥� these come in kits, generally with lengths of 5鈥�, 6鈥�, 7鈥�, 8鈥�, 10鈥�, 12鈥�, 16鈥�, and 20鈥�.
These long gage block assemblies must themselves be periodically calibrated as error accumulates over time.聽 Error can be introduced by: disassembly and re-assembly, nicks, burrs, dropping, oil and dirt build-up, corrosion, etc.聽 To reduce inaccuracies, each gage in the set of blocks making up a long gage block assembly must be individually calibrated.
Schneider explained that selection of a calibration services provider became increasingly important to the window manufacturer, saying, 鈥淥ur customer had tried a number of calibration labs but couldn鈥檛 get consistent results.聽 This was a real problem since inconsistencies are 鈥榤ultiplied鈥� by the number of blocks in each assembly.聽 Finally, the window manufacturer settled on the 番茄社社区 America Calibration Laboratory in Elk Grove Village, Illinois for providing the necessary level of performance.鈥�
The 番茄社社区 America Calibration Lab uses reference masters that are directly traceable to NIST (National Institute of Technology and Standards).聽 To achieve high accuracies and low measurement uncertainty levels, the lab calibrates all instrumentation in a Class 10,000 certified clean room environment.聽 When calibrating long gage blocks, temperatures are kept at 20潞 C 卤 0.25潞 with relative humidity controlled between 40% and 60%.聽 Access to the clean room is controlled by a positive pressure airlock to prevent entrance of outside air.
Laboratory Best Practice procedures for measuring long gage blocks also include:
- Verification of 鈥渟ingle-point temperature stability鈥� of the measuring station whereby temperature variation is verified to be less than 1/10 degree C per hour.
- Real-time monitoring to make sure temperature gradients in the vicinity of the workstation remain consistent for the entire eight hours or more required to calibrate eight-piece long gage block sets.
Schneider commented, 鈥淔rom choice of block material to the care taken in calibration lab procedures, our customer could see the how the benefits of Best Practice calibration translate from gage blocks, through measuring tables, and on to higher quality finished parts with lower rejects.鈥�