Standard Work · Lean Manufacturing

Corner Joint Gap Measurement Mitre Fold

Precision measurement of gap uniformity in corner joint mitre folds is a critical quality gate in lean sheet metal fabrication. This SOP defines the standard work for using a combination square and feeler gauge set to verify fit-up within ±0.005” before welding, eliminating rework and ensuring first-pass yield.

Estimated Time

15 min

Difficulty

Advanced

Regulation

CSA W59 / AWS D1.1

Version

1.0

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Purpose

To define the standardized method for measuring gap clearance in corner joint mitre folds prior to welding. Ensures consistent weld penetration, minimizes distortion, and supports lean objectives by reducing rework and scrap. Adherence to this procedure guarantees that every joint meets the dimensional tolerances required for subsequent assembly steps.

Scope

Applies to all sheet metal corner joint mitre folds (gauge 10–16) processed on the Accurpress press brake or equivalent equipment in fabrication bays 1 through 4. This procedure is mandatory for all setup technicians and operators performing mitre fold inspections. It covers the measurement of gap uniformity at the heel, midpoint, and toe of the joint.

Safety Precautions

LOTOLockout/Tagout press brake energy sources before making any tooling adjustments or measurements within the point of operation.
PPEWear cut-resistant gloves (ASTM F2992) when handling sharp mitred edges. Safety glasses with side shields are mandatory.
ERGOUse lift assists for parts over 20 lbs. Avoid pinch points between the work piece and the die during manual clamping.

Required Tools & Materials

Digital Caliper (Mitutoyo 500-196-30 or equivalent, 0.001" resolution)
Feeler Gauge Set (0.0015" – 0.025")
Combination Square with 4R Base (Starrett 12")
Deburring Tool + Mill File
Marking Pen (Sharpie Fine Point)
Inspection Checklist Printout

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Procedure: Step-by-Step

1 Deburr the mitred edges with a file to remove any raised burrs that could influence gap readings. Ensure the edge is straight and free of defects.

2 Place the work piece on a certified flat table or granite surface plate to ensure a stable reference plane for measurement.

3 Assemble the corner joint dry (no weld). Apply light clamping pressure at the heel and toe of the mitre to simulate the fit-up condition.

4 Using the combination square, check the 90° alignment of the mitre. Record any deviation from perpendicular in degrees on the inspection checklist.

5 Insert the appropriate feeler gauge into the joint gap at the midpoint. The gauge should fit with light drag. Record the gap measurement in inches.

6 Repeat the gap measurement at 3 distinct locations along the weld joint: heel, midpoint, and toe. Record all three readings.

7 If the gap at any location exceeds 0.010", reject the part and rework the mitre fold. If all measurements are within the specified tolerance, proceed to tack welding.

Corner Joint Gap Measurement Mitre Fold

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