Example data mode. The sample companies, offers and requests shown here are fictional (AI pictures) and are not counted in the figures below.
Lesson 4 of 7
Breaking the log down: headrigs and saw types
The machine that makes the first cut sets sawdust loss, dimensional accuracy, speed and the kinds of logs the mill can handle. Oklahoma State University Extension (USA, 2017) describes the headrig as a machine centre with four jobs: determine log geometry and grade, orient and fix the log, transport it, and cut it.
Kerf: the arithmetic behind every machine choice
Kerf is the width of the slot a saw cuts. Every millimetre of it becomes sawdust. The share of material lost per cut can be estimated with:
kerf share = kerf / (board thickness + kerf)
Worked example (own calculation, from kerf values used by a USDA Forest Service article, USA). For a 1 inch (25.4 mm) board:
| Saw example | Kerf | Share lost per cut |
|---|---|---|
| Circular headsaw | 0.300 in (7.6 mm) | 7.6 / 33.0 = about 23% |
| Band saw | 0.140 in (3.6 mm) | 3.6 / 29.0 = about 12% |
The calculation ignores planing allowance and drying shrinkage, so it shows direction, not mill results.
The five machine families
Band saws
A thin, flexible steel loop on two wheels. Its big advantage is the thin kerf. OSU Extension calls band saws "the most widely used headrig in many mills" and says they are flexible and relatively inexpensive. They suit hardwood mills, small and portable mills, and twin or quad arrangements in softwood. Their weakness is accuracy: stability depends on blade thickness, width, feeding force and guide spacing. Feed speeds in software examples were about 66 to 110 m/min; these are tutorial figures, not field measurements.
Circular saws
A rotating disc: stiff and tolerant of very high feed speeds, but it must be thick to stay flat, so the kerf of large headsaws is bigger. Circular saws dominate where speed matters more than ultimate recovery: multi-saw resaws, canter lines, edgers and trimmers.
Frame saws (sash gang saws)
Many parallel blades in a reciprocating frame cut a whole cant or log into boards in one pass. Rigid guidance gives consistent dimensions; blades are thicker and the stroke cycle limits feed speed (a manufacturer quote in one paper: 20 to 25 m/min). Mainly European, suited to uniform small logs and a few stable dimensions. In a Polish test on pine (Europe, 2023, six logs) the frame saw (about 4.0 mm kerf) and a horizontal band saw (about 2.5 mm kerf) gave yields about 70% and 73%; the difference was not statistically significant, and the frame saw was slightly more accurate.
Chipper-canters and profiling lines
They mill the outer slabs off as chips instead of sawing sideboards, then saws cut the cant into boards. They fit small softwood logs, where sideboards would be narrow, low-value pieces. Chips are a saleable by-product, so total fibre value can rise even if lumber yield is similar. A German vendor brochure (2020) quotes maximum feed speeds of 20 to 150 m/min for its chipper-canter; these are vendor claims and not independently verified. Open comparisons of recovery against saws are thin.
Curve sawing
Many softwood logs have sweep. Scanning determines the sweep and a computer pivots the saw to follow it. In a US study of hardwood logs (Hamner et al. 2006), lumber yield from the outside of curved logs rose 10 to 12% when curve sawn for logs with average sweep of 3.3 inches or more.
Thinner is not always better
A US simulation on red oak (Thomas and Buehlmann, 2022) found that cutting kerf from 0.16 to 0.12 inch on an 18 inch log gave a significant volume gain of 7.4 board feet, but that gains are now smaller than in earlier decades. In a laboratory frame-saw test (Europe, 2022), narrow-kerf blades had a static stiffness of 19.4 N/mm against 60.8 N/mm for wide-kerf blades: thinner blades deflect more and make dimensional errors.
Simple decision guide (the portal's synthesis, not a measured ranking)
- Small hardwood mill, variable logs, high-value grades: band headrig.
- Mid-size softwood mill: twin or quad band, or canter with circular saws.
- Uniform small logs, few stable dimensions: frame saw can be competitive.
Key points
- Kerf share per cut is kerf / (board thickness + kerf): about 23% for a 7.6 mm saw and 12% for a 3.6 mm saw on a 25.4 mm board.
- Band saws: thin kerf, flexible, less accurate; circular saws: fast, thicker kerf; frame saws: accurate, slow per frame; chipper-canters: chips instead of sideboards.
- A statistically insignificant difference (Polish test, six logs) does not prove the saws are equal.
- Thin kerf has diminishing returns and costs blade stiffness.
- Vendor feed speeds and tutorial figures are not independent proof of mill performance.