What is the difference between bow and spring in timber?

Bow is the deviation from flatness along the length of the wide face, while spring is the deviation along the length of the narrow edge.

How is the slope of grain measured?

It is measured by the deviation of the grain from the longitudinal axis of the piece, evaluated over a length of at least 250 mm.

Wane is the original rounded surface of the log (with or without bark) remaining on a piece of converted timber.

IS 3364

: 2000

Methods of measurement and evaluation of defects in timber, Part 2: Converted timber

CurrentSpecializedMethod of MeasurementMaterials Science · Timber and Timber Stores

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This standard specifies the methods for measuring and evaluating various natural and manufacturing defects in converted (sawn) timber. It provides standardized procedures to quantify defects like knots, shakes, splits, wane, and warp, which is essential for timber grading and quality control.

Methods of measurement and evaluation of defects in timber, Part 2: Converted timber

Quick Reference Values

Measurement of knotMaximum distance between lines enclosing the knot parallel to the longitudinal edges

Measurement of bowMaximum deviation from a straight edge connecting the two ends of the face

Measurement of cupMaximum deviation from a straight edge placed transversely across the width of the face

Measurement of springMaximum deviation from a straight edge connecting the two ends of the edge

Measurement of slope of grainMeasured over a distance of not less than 250 mm

Practical Notes

Moisture content heavily influences warp; always record the moisture content at the time of evaluating bow, cup, spring, and twist.

When measuring knots, it is crucial to distinguish between live (sound) knots and dead (loose/decayed) knots, as their structural implications differ.

Wane should be measured at the point of maximum reduction of the cross-section.