Surface Plate and Surface Table Calibration to BS 817:2008
AC Metrology calibrates granite and cast iron surface plates and surface tables to BS 817:2008, on site at your premises or in house in Derby. Every plate is measured with UKAS-calibrated equipment and comes with a certificate showing its overall flatness, local flatness and the grade it achieves. We cover the UK and Ireland, and aim to be on site within a week of your enquiry.
Why surface plate calibration matters
A surface plate is the reference for every height gauge, comparator and dial reading taken from it, so any error in the plate ends up in the measurement. Plates don’t wear evenly. Most work happens in the same few areas, which leaves local hollows, and chips.
Regular calibration shows whether the plate is still within tolerance for its grade, and gives you traceable evidence for audits and quality systems such as ISO 9001, which require measuring equipment to be calibrated at set intervals.
How we calibrate a surface plate
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Temperature stabilisation. The plate and our equipment are left to temperature soak and settle, and temperature is logged throughout, as a temperature gradient through the plate affects flatness readings.
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Cleaning and inspection. The working surface is cleaned and checked for chips, burrs and wear, and the supports are checked so the plate sits on its intended support points.
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Overall flatness survey. Using a Talyvel electronic level, we take readings along set lines across the working surface, following the Union Jack method, to map it and calculate the overall flatness deviation.
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Local flatness check. Repeat reading checks with a DTI across the surface pick up local wear that the overall survey can miss.
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Assessment against BS 817:2008. Results are compared with the tolerances for the plate’s size and grade.
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Certificate and advice. You receive a calibration certificate. If the plate is out of tolerance, we explain the options, such as resurfacing and lapping to restore flatness, or certifying the plate to a lower grade if that still suits the work.
On-site and in-house surface table calibration
Large plates and installed surface tables are calibrated where they stand, so they don’t need moving or re-levelling afterwards. Plates up to 3m x 1.5m can also be calibrated in house in Derby. The method, equipment and certificate are the same either way.
If a plate has been moved, re-supported or damaged since its last calibration, it’s worth having it checked before it goes back into use.
What your calibration certificate shows
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Overall flatness of the working surface
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Local flatness (repeat reading) results
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The BS 817:2008 grade the plate achieves
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Measurement uncertainty
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The equipment used and its calibration traceability
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Plate identification and calibration date
Equipment and traceability
We calibrate surface plates with a Talyvel electronic level, DTIs and temperature loggers. All of it is calibrated by UKAS-accredited laboratories, so every result on your certificate traces back to national standards.
Recalibration intervals and service contracts
We normally recommend calibrating surface plates every 12 months. Plates in heavy daily use, in production areas, or that have been moved may need checking more often.
For sites with several plates, a service contract puts every plate on the same schedule, so none get missed or drift out of date between audits:
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Each visit: cleaning, inspection, support and levelling checks, and calibration to BS 817:2008 with a certificate for each plate, with chip and damage repair on request
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Frequency: we recommend annual visits, but you choose the schedule
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Contract length: as long as you want, the longer the contract the cheaper the price
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Pricing: based on the number and size of plates, and contract length
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Reminders and records: we remind you before each visit and keep your calibration records
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Multiple sites: one contract can cover more than one site
Coverage, turnaround and experience
We work across the UK, including Scotland and Northern Ireland, and Ireland, and can travel internationally upon request. We aim to be on site within a week of your enquiry.
​Both directors have years of hands-on surface table calibration and resurfacing behind them: Luke as a field service engineer, and Andy over 11 years in metrology and precision engineering. Between them, the AC Metrology team has carried out more than 1,000 calibrations across a range of metrology equipment, with experience in aerospace, automotive, medical, nuclear, defence, rail, oil and gas, food and drink, precision engineering and QA labs.
Need a new plate rather than a calibration? See our granite surface plates and cast iron surface plates.
Surface plate calibration FAQs
How often should a surface plate be calibrated?
We normally recommend calibrating a surface plate every 12 months. Plates in heavy daily use, in production areas, or that have been moved or damaged may need checking more often. Your quality system may also set its own interval.
How is a surface plate calibrated?
The plate is cleaned, inspected and left to reach a stable temperature. A precision electronic level is then used to survey the overall flatness across the working surface, and repeat reading checks find local wear. The results are assessed against the tolerances in BS 817:2008 for the plate’s size and grade.
What does a surface plate calibration certificate show?
Our certificates show the overall flatness of the working surface, the local flatness (repeat reading) results, the BS 817:2008 grade achieved, the measurement uncertainty, and the equipment used along with its calibration traceability.
Can you calibrate surface plates on site?
Yes. Large plates and installed surface tables are calibrated on site across the UK and Ireland, so they don’t need moving. Smaller plates can also be calibrated on site or in our facility in Derby. The method and certificate are the same either way.
What happens if my surface plate fails calibration?
A plate that is out of tolerance can usually be brought back within its grade by resurfacing and lapping, which we can often do on site. If the plate will still do the job at a lower grade, it can be certified to that grade instead.
Do you offer surface plate service contracts?
​Yes. A service contract puts every plate on site on a fixed schedule, with cleaning, inspection and calibration to BS 817:2008 at each visit. We send reminders and keep your calibration records, contracts can cover more than one site, and prices are based on the number and size of plates, as well as contract length.