Sorting rules: diameter, quality and form

Sorting is where one lot of logs becomes several products with several prices. Sorting rules decide which logs go to which sawline, which price class applies, and how much of the lot is downgraded. This lesson covers the quality ladders, the form criteria and the diameter and taper effects the portal's sources quantify.

The A-D ladder

The RVR (Germany, Europe) uses four quality classes: A (excellent, flawless or only insignificant defects), B (normal, few or moderate defects), C (normal, more frequent or stronger defects) and D (usable as stem wood but not meeting A to C). The minimum section length is 3 m for classes A and B. Mixed grades such as B/C must be agreed in the contract, because without a rule the lot has no clear price.

Poland's State Forests (Europe, mod2024 documents) use a similar A-D ladder with quantified limits. For conifer long logs of 6.1 to 14.0 m, produced in bark and measured piece by piece, the extracted sweep limits are 1 cm per metre (A), 2 (B), 3 (C) and 5 (D). Internal and diffuse rot are allowed in no class, end-face blue stain is not allowed in class A, and side stain is allowed up to 3 mm deep in some classes. The extracted tables were partly garbled, so confirm the limits from the current text before applying them.

The letter schemes look alike but are not equivalent: a "B" in one system is not a "B" in another.

European standards

Visual quality classification of round timber sits in the EN 1927 series for softwoods and EN 1316 for hardwoods. Catalogue pages show EN 1927-1:2008 for spruces and firs, and EN 1316-1:2012 for oak and beech. Feature measurement is covered by EN 1309-3:2018, which for round timber serves appearance grading only and requires the method to be stated. These standards are paywalled and the portal did not read the class limits, so none are quoted. A contract should name the part and the edition.

Form: taper, sweep and the log you cannot see

Grade is not the only sorting variable. Form decides how much of the log fits into boards.

Taper. In the Blinzer and Treml (2022, Austria, Europe) example for a glued-laminated lamella 43 x 146 x 4,000 mm sawn with a three-stem pattern, the sawn volume per log is 0.075 m3 whatever the taper. With log volumes of 0.152, 0.181 and 0.212 m3 for taper of 5, 15 and 25 mm, the main-product yield is 0.075 / 0.152 = 49.3%, 41.4% and 35.4%. A mill needing 30 m3 of lamella needs 30 / 0.075 = 400 pieces, which means 400 x 0.152 = 60.8 m3 of low-taper logs or 400 x 0.212 = 84.8 m3 of high-taper logs, 39.5% more wood (own calculations; main product only, one pattern).

Reaction wood and shake. An off-centre pith with wider rings on one side suggests reaction wood, and ring or star shake shows on the end face; mild reaction wood is hard to see even on fresh surfaces, so end-face inspection is a screening step, not a guarantee (ws-d1 article).

Diameter as a sorting variable

Small logs recover less. In a simulation of Swedish spruce and pine (Fredriksson et al. 2015, Europe), reference cant sawing gave a planed-board yield of 43.7% of log volume for all logs but only 35.8% for the 2,214 logs with top diameter under 185 mm, about 7.9 points lower (own subtraction). How the small logs are sawn changes this: live sawing with trapeze edging into 24 to 46.5 mm green boards for cross-laminated timber layers gave 53.2% for the small logs (a simulation of a different product).

For oak, the Croatian simulation RadSawSim (Forests, 2025, Europe) compared live sawing with radial techniques on 320 virtual logs of 25 to 100 cm. Live sawing maximised log-value yield below about 45 cm; radial sawing, especially fourths and fifths, was generally better above it. The authors assumed quality weights of 1.0 (radial), 0.9 (half-radial) and 0.8 (tangential), and the result was mixed near the threshold. A mill might use 45 cm as a starting rule for which oak logs go to a radial line, then refine it with its own board prices.

Juvenile wood adds a second reason (ws-d2 article): top logs and fast-grown stands carry more low-density core wood, so sort by small-end diameter and by stand or supplier, and do not rely on ring width alone.

Key points

• The RVR (Germany) has classes A to D, a 3 m minimum section for A and B, and requires mixed grades such as B/C to be agreed.
• EN 1927 (softwood) and EN 1316 (hardwood) exist, but class limits are paywalled and not quoted; name part and edition in the contract.
• For a fixed 0.075 m3 product, yield falls from 49.3% to 35.4% as taper rises from 5 to 25 mm, so the mill needs 39.5% more log volume (own calculation).
• Small logs recover less: 35.8% against 43.7% in a Swedish simulation (Europe).
• In the oak simulation live sawing won below about 45 cm; the threshold depends on the assumed board price premium.