Gear Cutting Machine Accuracy Inspection

⌖How to inspect

• Check hobbing machine accuracy against the standard's test itemsHobbing machine

  ToolsPer the standard's test methods (geometric accuracy and machining accuracy follow the methods of ISO 230-1)

  ProcedureJudge by three things: geometric accuracy, machining accuracy (measuring a test-cut gear), and kinematic accuracy (accuracy of motion transmission between the hob spindle and the table rotation)

  TolerancesTolerances of JIS B 6216 and ISO 6545 (the standard text is paid, so it was not read)

  At acceptance, and after an overhaul or major repair. ISO 6545 also defines terms for the machine's main elements

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• Measure the runout of the hob hub mounted on the hobbing machineHobbing machine

  ToolsDial indicator (lever type)

  ProcedureCheck the arbor runout first, then put the indicator on the outer diameter and end face of the hubs at both ends of the hob and rotate. If the runout at both ends is in the same direction it is eccentricity; if opposite, it is tilt (wobble)

  TolerancesTolerances by hob grade (the US AGMA hob standard that Cluff cites sets hub runout by grade. The Japanese hob accuracy standard is JIS B 4355)

  Cluff says that hob runout at mounting and sharpening is the largest cause of poor tooth profile in hobbing

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• Measure the flute spacing, radial alignment (rake), and flute lead of a sharpened hobHobbing machine

  ToolsTwo center stands, straight mandrel, two lever-type dial indicators (0.002 mm resolution), gauge blocks, micrometer (or a dedicated hob measuring machine if available)

  ProcedureFlute spacing and radial alignment are measured as described in the tool care section. An error in flute lead appears as taper in the hob's outside diameter, so it can be found indirectly from the difference between readings at the high points of the teeth at both ends of the same row (Moderow)

  TolerancesTolerances by grade in JIS B 4355 and ISO 4468

  Sharpening errors cannot be seen with the naked eye, so measure after every sharpening (Moderow)

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• Watch the change in tooth thickness while shifting the hobHobbing machine

  ToolsOver-pin (ball) micrometer, span micrometer

  ProcedureRecord and compare tooth thickness at the start and end of a shift (or every set number of parts)

  TolerancesTooth thickness tolerance

  A hob whose flute lead was wrong at sharpening becomes tapered, and tooth thickness changes as the hob is shifted (Cluff, Liston). With multi-shift, hob runout may change tooth thickness and tooth profile (Nidec Machine Tool)

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• Check how tooth thickness moves from a cold state to a warmed-up stateHobbing machine

  ToolsOver-pin (ball) micrometer

  ProcedureMeasure and record tooth thickness at set intervals starting right after startup

  TolerancesTooth thickness tolerance (Kashifuji says that with its compensation device, over-pin dimension can be held within ±10 µm even from a cold start)

  Also serves to confirm that thermal displacement compensation and spindle/table axis cooling are working

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• Judge tooth profile pass/fail with the same measuring machine, the same tooth, and the same control pointsShaving machine

  ToolsGear tester

  ProcedureIf test-cut judgments disagree, first suspect differences in the measuring machine (machine-to-machine difference), the tooth measured, and the tooth profile control points. Also check differences in the test-cutting machine, in machining conditions, and in the accuracy of the preceding operation (rough gear cutting) (Nidec Machine Tool)

  Tolerances—

  The standard for inspecting the measuring machine itself is JIS B 1758 (acceptance inspection of gear measuring instruments)

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• Inspect ground tooth surfaces for grinding burn (surface temper) by chemical etchingGear grinding machine

  ToolsEquipment and reagents of JIS B 1756

  ProcedurePer the standard's procedure (the text is paid)

  TolerancesPer the drawing or the customer's instructions

  A method for finding light grinding burn invisible to the eye; it can also be used to find abnormalities in hard turning after heat treatment and in carburizing or decarburizing (preview)

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• Read the tooth profile and lead charts of cut gears and isolate the cause in the tool or machineCommon

  ToolsGear tester (measures tooth profile, lead, and pitch)

  ProcedureRead tooth profile through three values — total profile deviation, profile form deviation, and profile slope deviation — and lead through three — total helix deviation, helix form deviation, and helix slope deviation (referenced to the mean line within the evaluation range). If the profile is tilted (slope deviation), suspect rake angle, radial alignment, or hub runout; if wavy, flute spacing, hub runout, or the hob bore; for a poor lead, machine accuracy or the fixture (Nidec Machine Tool's trouble chart)

  TolerancesAccuracy grade on the drawing (JIS B 1702-1)

  Symbols differ between JIS/ISO and DIN (against fHα, Fα, ffα in JIS/ISO, DIN uses fHα, Ff, ff, etc.). A diagram showing how to read the charts is in Nidec Machine Tool's material

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• At periodic inspections, measure and correct axis alignment, runout, level, and reference positionCommon

  ToolsManufacturer's inspection tools

  ProcedureGleason's inspections check axis alignment and runout in a quick inspection, and go as far as machine leveling, geometric accuracy, and reference position adjustment in higher-level inspections. The company teaches in courses how to determine each axis's reference dimensions and enter them in the machine data, and common mistakes and their effects. Kashifuji inspects the accuracy of each unit at overhaul and carefully re-checks the accuracy of critical parts

  TolerancesPer-machine inspection certificates and standard tolerances

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≡Related standards

• Hobbing machineJIS B 6216:1998 Gear hobbing machines — Testing of the accuracy / ISO 6545:1992 (modified adoption = MOD). Draft prepared by the Japan Machine Tool Builders' Association. JIS confirmed in 2023In addition to geometric accuracy tests and machining accuracy tests for hobbing machines (per ISO 230-1), ISO 6545 specifies a kinematic accuracy test that checks the accuracy of motion transmission. The ISO side is under review (90.92) and a revision is in progress. In the ISO list of machine tool accuracy tests (ICS 25.080.20), this is the only gear machine tool standard, and no ISO or JIS accuracy test standards were found for gear shapers, gear grinders, or shaving machines^[1][2][3]
• Hobbing machineJIS B 4355:2016 Gear hobs — Accuracy requirements / ISO 4468:2009 (MOD). On the ISO side, the 2020 edition (3rd edition) is currentJIS is the standard for the accuracy and test methods of hobs of module 0.1–40, reference pressure angle 20°, 1–7 starts, outside diameter 24–400 mm, and overall length 8–510 mm (preview). ISO 4468:2020 divides general-purpose hobs of module 0.5–40 into seven grades, 4A, 3A, 2A, A, B, C, and D (4A is the highest), and sets tolerances for element-by-element tests and for composite tests along the cutting edge. It also includes the methods for inspection after sharpening (flute spacing and radial alignment)^[4][5][6]
• Hobbing machineJIS B 4354:2013 Gear hobs — Part 1: Solid hobs, shape and dimensions / ISO 2490:2007 (MOD)Standard for dimensions such as hob bore diameter and hub. Only the title and the corresponding ISO standard were confirmed (the text is paid)^[7](1 source, for reference)
• Gear shaperJIS B 4356:2024 Pinion cuttersStandard for pinion cutters for involute spur and helical gears of module 0.2–12 mm and reference pressure angle 20°. Revised in 2024 (replacing the 2009 edition). The corresponding international standard could not be confirmed from the JSA bibliographic record^[8][9](1 source, for reference)
• Shaving machineJIS B 4357:2000 Round shaving cutters (confirmed in 2026)The corresponding international standard could not be confirmed from the JSA bibliographic record^[10](1 source, for reference)
• CommonJIS B 1702-1:2016 Cylindrical gears — System of accuracy — Part 1: Definitions and allowable values of deviations relevant to flanks of gear teeth / ISO 1328-1:2013 (MOD)The reference for the accuracy of cut gears. Details of gear accuracy are on Kezuriba's gears page^[11](1 source, for reference)
• CommonJIS B 1758:2013 Acceptance inspection of gear measuring instrumentsStandard for inspecting the measuring machines that measure gear accuracy. The pinion cutter standard (JIS B 4356) also cites it^[12][9](1 source, for reference)
• Gear grinding machineJIS B 1756:2017 Gears — Surface temper etch inspection after grinding, chemical method / ISO 14104:2014 (MOD). Draft prepared by the Japan Gear Manufacturers AssociationA method for finding light grinding burn (surface temper) that cannot be seen by eye, using chemical etching. It is more sensitive to changes in surface hardness than ordinary hardness testing, and the standard says this method is preferable for detecting surface temper. It applies to steel gears (preview)^[13][14](1 source, for reference)
• CommonJIS B 6016-2:1998 Machine tools — Lubrication systems / ISO 5170:1977 (MOD). The method for showing lubrication diagrams is JIS B 6016-1:1998Only the title and the corresponding ISO standard were confirmed (the text is paid)^[15](1 source, for reference)

The standard texts are paid, so tolerances are written from sources such as in-house standards published by machine manufacturers. For the correspondence between standards, see the standards correspondence table as well.