Calibration
All measurement results are wrong but some are more wrong than others! In 90% of the failures Design Unit investigate, excessive geometry errors contributed to the failure.
Gear tolerances are small - often less than 10µm which means the measuring machine accuracy (or measurement uncertainty) is often a significant proportion of the tolerance. In practical terms it means we incorrectly reject gears which are within tolerance and accept gears which are outside tolerance. Most people don’t know their measurement capability but it is easy to quantify if you follow the guidance in ISO 18653 and it saves making potentially very expensive mistakes.
ISO 18653 ‘Evaluation of instruments from the measurement of gears’ recommends that measuring machines are calibrated using ‘workpiece like artefacts’ with a geometry as similar in size, weight and design as possible to the product gears inspected on the measuring machine. See examples.
NGML offer two UKAS accredited services to help gear manufacturers:
- Gear and gear artefact calibration service. We calibrate your gears with the lowest uncertainty in the UK and then you apply ISO 18653 procedures to estimate measurement uncertainty.
- An on-site calibration service. We bring a selection of the UK's national master gears and calibrate your machine, quantifying measurement uncertainty with some of the most accurate master gears and artefacts in the world. Again this is performed in accordance with ISO 18653.
As a National Laboratory the NGML offers the lowest measurement uncertainty of all the accredited calibration laboratories within the UK. The current UKAS schedule of accreditation demonstrates that the best measurement capability of ±1.0μm for helix and profile slope parameters and adjacent pitch parameters. It also shows that the lab is capable of calibrating large gear artefacts and master gears, suitable for many industrial applications.
The capability of the Klingelnberg P65 reference machine is verified by comparison with the German National Laboratory, PTB and the USA National Laboratory Y12, at the Oakridge Metrology Centre. The results from the last comparison exercise show the Klingelnberg P65 agrees with PTB and Y12 within 1.0μm on all gear parameters.