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Notes on dimensioning and inspection.

Specific points on tolerances, GD&T, scanned drawings and first article packages. No product news dressed up as articles.

22 July 2026ISO 286, tolerances, inspection
Converting an ISO 286 fit into numerical limits
How to go from an H7 or h7 read on a drawing to the two limits in millimetres you actually inspect, with the method, IT values and a full example.
24 June 2026AS9102, FAI, concession, quality
Handling a concession on an AS9102 FAI report
A practical guide to handling a concession on an AS9102 FAI report, filling in Form 3 and the corrective actions to approve.
19 June 2026ISO 2768, ISO 2768-vL, general tolerances
ISO 2768-vL general tolerance and its limits
How to apply the ISO 2768-vL general tolerance to very coarse parts, with the class L geometric tolerances and an example.
15 June 2026ISO 286, m6, fit, metrology
Calculating the m6 fundamental deviation and its limits
A complete method for calculating the m6 fundamental deviation to ISO 286: deviation table, limits in mm and a dimensional inspection example.
10 June 2026ISO 286, k6, fit, metrology
Calculating the k6 fundamental deviation and its limits
How to find the k6 fundamental deviation to ISO 286: calculating the limits of a transition fit, with a worked example.
5 June 2026ISO 1101, profile of a surface, GD&T, metrology
ISO 1101 profile of a surface tolerance
A complete method for inspecting an ISO 1101 profile of a surface tolerance on a CMM by comparison with the CAD model, with a worked example.
1 June 2026ISO 1101, profile of a line, GD&T, metrology
ISO 1101 profile of a line tolerance
How to inspect an ISO 1101 profile of a line tolerance by CMM probing or on a profile projector, with a worked example.
27 May 2026Tr thread, ISO 2903, gauge wires, metrology
Inspecting a Tr trapezoidal thread
A practical method for inspecting a Tr trapezoidal thread to ISO 2903: calculating the pitch diameter with gauge wires and thread gauges.
22 May 2026ISO 3611, micrometer, calibration, metrology
Calibrating a micrometer to ISO 3611
A complete method for calibrating an outside micrometer to ISO 3611: gauge blocks, anvil parallelism and error calculation.
18 May 2026ISO 13385, caliper, calibration, metrology
Calibrating a vernier caliper to ISO 13385
The calibration procedure for a caliper to ISO 13385-1: inspection points, gauge blocks, MPE tolerances and the calibration record.
13 May 20265M, uncertainty, metrology, ISO 14253
Calculating measurement uncertainty with the 5M method
How to calculate measurement uncertainty with the 5M diagram (Material, Milieu, Means, Method, Manpower), with a worked application.
8 May 2026ISO 1101, angularity, sine bar, GD&T
ISO 1101 angularity tolerance and the sine bar
How to calculate and inspect an ISO 1101 angularity tolerance on a sine bar and a CMM, with a worked example.
4 May 2026chamfer, metrology, inspection, machining
Inspecting a mechanical chamfer, and its limits
A rigorous method for inspecting a 45° or 30° chamfer with a chamfer gauge and a dial indicator, with a worked example.
29 April 2026ISO 1101, symmetry, GD&T, metrology
ISO 1101 symmetry tolerance and how to inspect it
How to calculate and inspect an ISO 1101 symmetry tolerance relative to a median datum plane, with a worked example.
24 April 2026AS9102, ballooning, mechanical drawing, FAI
How to balloon a mechanical drawing for AS9102
A practical guide: how to balloon a mechanical drawing without missing anything, balloon numbering rules and preparing the FAI package.
20 April 2026ISO 1101, cylindricity, GD&T, metrology
ISO 1101 cylindricity tolerance and its limits
How to inspect an ISO 1101 cylindricity tolerance by CMM scanning, with a worked example and an analysis of the deviations.
15 April 2026ISO 1101, roundness, GD&T, metrology
ISO 1101 roundness tolerance and how to measure it
A practical guide to measuring an ISO 1101 roundness tolerance with a dial indicator on a V-block or a roundness tester, with a worked example.
10 April 2026ISO 286, H7 f7, clearance, fit
H7/f7 fit: maximum and minimum clearance
A complete method to work out the maximum and minimum clearance of an ISO H7/f7 running fit, with a table and a worked example.
6 April 2026ISO 286, H7 p6, interference, fit
H7/p6 fit: calculating the exact interference
How to calculate the maximum and minimum interference of an H7/p6 press fit to ISO 286, with an assembly example.
1 April 2026centre distance, gauge pins, metrology, inspection
Checking the centre distance of two holes without a CMM
A step-by-step method for checking the centre distance of two holes with gauge pins and a caliper or an outside micrometer.
27 March 2026ISO 1101, straightness, GD&T, metrology
ISO 1101 straightness tolerance and how to inspect it
How to check an ISO 1101 straightness tolerance on an axis or a cylinder generating line, with a worked inspection example.
18 March 2026ISO 1101, flatness, GD&T, metrology
ISO 1101 flatness tolerance on a surface plate
A practical method for inspecting an ISO 1101 flatness tolerance on a granite surface plate and a CMM, with a worked example.
13 March 2026ISO 286, g6, fit, metrology
Calculating the g6 fundamental deviation and its limits
How to calculate the g6 fundamental deviation to ISO 286, with the table of IT6 values, es/ei deviations and a machining example.
9 March 2026ISO 2768, ISO 2768-fH, tolerances, metrology
ISO 2768-fH general tolerance and the calculations
A full explanation of the ISO 2768-fH general tolerance: tables of fine deviations and geometric class H, with an applied example.
4 March 2026ISO taper, gauge pins, metrology, inspection
Inspecting an ISO taper with gauge pins, and the calculation
Formulas and method for inspecting an ISO taper with calibrated gauge pins and a micrometer, with a worked acceptance example.
27 February 2026ISO 1101, parallelism, GD&T, metrology
ISO 1101 parallelism tolerance and how to measure it
A rigorous method for inspecting an ISO 1101 parallelism tolerance on a surface plate and a CMM, with a full worked example.
24 February 2026AS9102, FAI, Form 2, special processes
How to fill in AS9102 Form 2 without errors
A practical guide to filling in AS9102 Form 2: raw material traceability, special processes and certificates of conformance.
18 February 2026AS9102, FAI, Form 1, quality
How to fill in AS9102 Form 1 of the FAI
A complete method for filling in AS9102 Form 1 of the first article inspection, with the list of fields and an example.
13 February 2026ISO 1101, perpendicularity, GD&T, metrology
ISO 1101 perpendicularity tolerance on a surface plate
A practical guide to measuring an ISO 1101 perpendicularity tolerance on a surface plate with a precision square, a dial indicator and a worked example.
9 February 2026ISO 286, H7, h7, tolerances
Calculating the H7 and h7 fundamental deviations in mm
A step-by-step method for finding the H7 and h7 fundamental deviations to ISO 286, with the table of IT7 intervals and an inspection example.
2 February 2026ISO 965, thread, gauge wires, metrology, inspection
Inspecting an ISO metric thread with wires and gauges
A practical method for inspecting an ISO metric thread with thread ring gauges and the three-wire method, with calculations and an example.
16 January 2026ISO 1101, coaxiality, GD&T, metrology
ISO 1101 coaxiality tolerance: calculation and inspection
How to calculate and inspect an ISO 1101 coaxiality tolerance, with the surface plate measuring method and a worked example.
7 January 2026ISO 21920, roughness, Ra, Rz, metrology
Ra vs Rz roughness: difference, measurement and limits
The difference between Ra and Rz, choosing the λc cut-off, evaluation length and the 16% rule under ISO 21920, with an inspection example taken to a verdict.
22 December 2025tolerance stack-up, worst case, tolerancing, design office
Calculating a tolerance stack-up by the worst-case method
A detailed method for a worst-case tolerance stack-up: closing equation, limits and a full worked example.
9 December 2025ISO 1101, ISO 2692, MMC, position, GD&T
ISO 1101 position tolerance at maximum material condition
How to calculate an ISO 1101 position tolerance at maximum material condition (MMC), with bonus tolerance and a worked example.
25 November 2025scan, OCR, digitisation, CAD, metrology
Why my scanned drawing reads badly, and the fixes
Why a scanned drawing reads badly with OCR, and practical ways to improve the scanning and recognition of your drawings.
14 November 2025ISO 2768, ISO 2768-mK, general tolerances, metrology
ISO 2768-mK general tolerance for a 250 mm dimension
Working out the ISO 2768-mK general tolerance on a 250 mm dimension: dimensional limits, geometric tolerance and an inspection example.
30 October 2025AS9102, FAI, aerospace, quality
How to fill in AS9102 Form 3 without errors
A step-by-step guide to filling in AS9102 Form 3 of the FAI package, with the recording method and a concrete example.
20 October 2025ISO 1101, runout, GD&T, metrology
The difference between circular runout and total runout
The difference between circular runout and total runout under ISO 1101, how each is measured, and a worked example.
6 October 2025ISO 286, js9, tolerances, metrology
Calculating the js9 fundamental deviation and its limits
A complete method for calculating the js9 deviation on a mechanical drawing, with the table of IT9 values, limits in millimetres and an example.

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