Traceability, intervals and what to expect from a good calibration partner - explained for quality and engineering teams.
Calibration is the evidence that the numbers on your inspection reports are defensible. Without a traceable, accredited chain, a customer dispute over a rejected part becomes an argument you cannot win. AS9100, IATF 16949, ISO 13485 and Nadcap all require it - but the deeper reason is commercial: measurements that customers can audit are measurements customers will trust.
ISO/IEC 17025 accreditation, granted in the UK by UKAS, is not a rubber stamp. It confirms that the calibration laboratory operates a quality system, uses qualified staff, and issues results traceable through a documented chain to national standards (NPL in the UK) and ultimately to SI units. A certificate that carries the UKAS crown is fundamentally different from a certificate that only claims 'traceable' - only the accredited certificate can be relied on in an audit or dispute.
CMMs are calibrated per ISO 10360-2/-5, with length errors (MPE_E) verified using calibrated step gauges or ball bars, and probing errors (MPE_P) using a calibrated sphere. Portable arms follow ISO 10360-12. Optical scanners are covered by ISO 10360-8 and VDI/VDE 2634. Hand tools, gauges and setting rings are verified against calibrated masters. Different standards, one principle: the check artefact must be traceable to a higher order than the equipment being checked.
A default 12-month interval is administratively convenient but rarely optimal. Best practice is a risk-based interval driven by usage, environment, historical drift and the consequence of an out-of-tolerance condition. A CMM in a temperature-controlled room measuring critical aerospace features may need six-month intervals; a shop-floor gauge in benign use may safely extend to 18 or 24 months.
For fixed CMMs, on-site calibration is normal - transporting a bridge CMM is more damaging than any small accuracy penalty from field calibration. For portable arms, gauges and hand tools, off-site laboratory calibration usually gives lower declared uncertainty and shorter turnaround. We help clients decide the right split, negotiate multi-year contracts and coordinate scheduling across multiple sites.
An out-of-tolerance calibration result is a quality event, not a paperwork exercise. It triggers a formal review of parts measured since the last known-good calibration, a decision on rework, recall or accept-in-place, and a documented corrective action. The escalation route should be agreed with the calibration partner before the first certificate is issued - not discovered under pressure during an audit.
We are not a calibration lab - we work with a network of UKAS-accredited partners across the UK and help clients choose the right provider, negotiate service contracts and defend calibration decisions in customer audits. Our advice is free to the end user.
No - we deliberately don't. Being independent of any calibration lab means we can recommend the right accredited partner for your equipment and location, and support you honestly if an existing provider is not delivering.
A UKAS on-site calibration of a mid-size bridge CMM in the UK is typically 1,200 to 2,500 GBP depending on volume and features. Multi-year contracts and multi-machine sites reduce the per-machine cost significantly.
Sometimes - if drift data supports it and customers accept it. We help build the risk-based case. But cutting corners on calibration is almost always false economy compared with a rejected batch or a lost customer audit.
If they are UKAS (or equivalent national accreditation body) accredited, cover the correct scope, state uncertainty properly and are current - yes, in every audit we've supported.
Tell us about the parts, tolerances and timing. We'll shape an impartial route through our trusted UK partner network - at no cost to you.
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