Sawing patterns: live, cant and quarter sawing in beech

The three basic patterns

A sawing pattern is how the log is divided into boards. Three families appear throughout the articles:

A beech experiment from Slovakia

Vilkovsky, Klement and Vilkovska (2023, Applied Sciences, Slovakia, Europe) compared the three patterns on six beech logs (two per pattern; mid diameters 43 to 60.5 cm; 4.0 to 4.2 m long) on a horizontal band saw, target thickness 33 mm. Quantitative yield is total lumber volume divided by log volume. Qualitative yield is the share of radial lumber, that is, cut with rings roughly perpendicular to the face.

Cant sawing gave the highest volume, quarter sawing the highest radial share. The ANOVA showed a significant pattern effect on radial share (p = 0.0105) but not on quantitative yield (p = 0.1721).

Why be careful. Two logs per pattern gives very little statistical power. Pattern and log size are mixed up, because the smallest logs went to live sawing and the largest to cant sawing, so part of V4's 84 percent comes from its size. The paper has internal inconsistencies (log length, the "17.3 percent" statement in the abstract that cannot be derived from the tables), and the yields are not clearly with or without bark. Read it as an illustration of a trade-off, not a benchmark.

Pattern interacts with the product

In the Swedish CLT simulation (Fredriksson et al. 2015, Europe), live sawing with trapeze edging of logs under 185 mm top diameter into 24 to 46.5 mm boards gave 53.2 percent of log volume against 35.8 percent for reference cant sawing, a gain of 17.4 points. For the full log range, a cant-based CLT process gave 42.8 against 43.7 percent, no gain. A different pattern wins for a different product and log size.

Steele (1984, North America, old simulation results) reports that shifting the opening face by 0.2 inch on an 8-inch log can change recovery by 25 percent, and that offset rather than centred sawing probably raises recovery by 5 to 10 percent. Use these as order of magnitude only.

Worked example: how much premium does quarter sawing need?

Using the mean beech yields above, suppose a mill gets price P per m3 for cant-sawn boards. How much more per m3 must quarter-sawn boards earn to produce the same revenue per m3 of log?

• Revenue per m3 of log, cant: 0.7850 x P.
• Quarter: 0.6126 x P_q. Equal when P_q = P x 0.7850 / 0.6126 = 1.281 P.
• Required premium: about 28 percent on all quarter-sawn output.

This is portal arithmetic from six logs, ignoring costs, throughput and the fact that not all quarter-sawn output is radial (about 55 percent was). Use your own price list and cost data.

Checklist: running your own pattern trial

• Allocate logs to patterns so that size, taper and defects are balanced across patterns.
• Record red heartwood, reaction wood, curvature and ovality per log.
• State bark treatment and lumber state.
• Evaluate on value, not only volume.

Key points

• The pattern that maximises volume (cant, 78.5 percent mean) was not the one that maximises radial content (quarter, 55 percent mean) in the Slovak beech experiment.
• The six-log sample confounds pattern with log size; only the radial effects were statistically significant.
• Pattern effects depend on product: live sawing won for CLT boards from small logs in Sweden but not across all log sizes.
• A volume loss can be compared with a price premium using a simple break-even ratio (here about 1.28).
• Always test patterns against your own price lists.