Press accuracy inspection

⌖How to inspect

• Know the press accuracy grade, and watch for deterioration with an annual accuracy inspectionMechanical press

  ToolsMeasuring tools that comply with the standard (dial indicator, cylindrical square, etc. JIS B 6402 cites JIS B 7539, the standard for cylindrical squares and coordinate measuring machines)

  ProcedureMeasure the static accuracy items of JIS B 6402 and compare them with the grade at delivery

  TolerancesTolerances for each JIS B 6402 grade (special grade, grade 1, grade 2, grade 3). Check the values in the standard text

  AIDA recommends an annual accuracy inspection, because lower accuracy causes variation in product accuracy, shorter die life, and more noise and vibration. Dynamic accuracy (under load) is hard to measure and evaluate, and there is no official specification for it

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• Straightness of the bolster (bed) top surface and the slide bottom surfaceMechanical press

  ToolsStraightedge, dial indicator, etc.

  ProcedureMeasure whether each of the die mounting surfaces is flat

  TolerancesDepends on the JIS B 6402 grade

  If poor, the die deforms during working, causing poor product accuracy and die breakage (AIDA)

  ^[3](1 source, for reference)

• Parallelism between the slide bottom surface and the bolster top surfaceMechanical press

  ToolsDial indicator

  ProcedureMeasure how parallel the upper and lower mounting surfaces are, as a pair

  TolerancesDepends on the JIS B 6402 grade

  If poor, the upper and lower dies do not meet parallel, which matters especially in coining and sizing (AIDA)

  ^[3](1 source, for reference)

• Squareness of the slide's vertical motion to the bolster top surfaceMechanical press

  ToolsCylindrical square, dial indicator

  ProcedureCheck whether the slide moves straight up and down relative to the bolster top surface

  TolerancesDepends on the JIS B 6402 grade

  If poor, the upper and lower dies go out of alignment. The effect is large when blanking thin sheet (AIDA)

  ^[3](1 source, for reference)

• Squareness of the shank mounting hole to the slide bottom surfaceMechanical press

  ToolsDial indicator, test bar

  ProcedureOn a press with a shank hole, check the squareness of the hole to the slide bottom surface

  TolerancesDepends on the JIS B 6402 grade

  ^[3](1 source, for reference)

• Total clearance of the upper and lower jointsMechanical press

  ToolsDial indicator

  ProcedureMeasure the total clearance in the joints (connecting rod, crank, gib, etc.) when the slide is moved up and down

  TolerancesDepends on the JIS B 6402 grade. The smaller, the better

  Large total clearance increases breakthrough (the shock at the moment of blanking), which causes die wear, vibration, and noise. It grows with wear over the years. Play caused by wear or deformation of moving parts can be brought back by replacing parts with new ones or by corrective machining (overhaul) (AIDA)

  ^[3][5][6](1 source, for reference)

• Match between the rotation angle indicator and the slide positionMechanical press

  ToolsDial indicator

  ProcedureFind the slide's bottom dead center with a dial indicator, then read the rotation angle indicator at that point

  TolerancesThe slide position and the indicated value must agree (Specified Self-Inspection Standard). For presses with a positive clutch, on single-stroke operation the angle between top dead center and the actual stopping point must be within 10 degrees

  ^[7](1 source, for reference)

≡Related standards

• Mechanical pressJIS B 6402:2020 Mechanical presses - Accuracy grades and inspection of accuracy (draft prepared by the Japan Forging Machinery Association)Covers general-purpose single-action crank presses and single-action crankless presses. Excludes hot forging presses, link presses, and presses of special construction. Accuracy has 4 grades: special, 1, 2, and 3 (JIS preview)^[1][2][3]
• Hydraulic pressJIS B 6403:2020 Hydraulic presses - Accuracy grades and inspection of accuracyCovers hydraulic presses used for blanking, bending, forming, and drawing of sheet metal. Excludes horizontal presses, column-type presses without slide guides, and presses of special construction; press brakes are also excluded as special construction. There are 4 grades, special to grade 3 (JIS preview)^[4][2]
• CommonJIS B 6411-1 (adopted with modifications from ISO 16092-1) Presses - Safety - Part 1: General safety requirements; JIS B 6411-2 (ISO 16092-2) Part 2: Safety requirements for mechanical pressesPart 1 does not apply to press brakes or turret punch presses. In JFMA's list, Part 1 was established on 2025-03-25^[2](1 source, for reference)
• CommonJIS B 0111 Presses - TerminologyThe terminology standard cited by JIS B 6402 and 6403. JFMA takes its definition of a press from this standard^[1][2]

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.