$ ./rotarypeelcalc

RotaryPeelCalc

A peeling recipe from the dry sheet backwards. Pick a species, enter the thickness, length and width the sheet has to measure after drying and the moisture content it has to measure them at, and the three lathe-line settings come back: green peel thickness, score length and clip width.

// shrinkage from Wood Handbook Table 4-3 and equation 4-9 (FPL-GTR-282, 2021); the allowances are stated defaults, not measurements. Try poplar at 8 %

// where the numbers come from, and the whiteboard they replace, are in the write-up

SPECIES AND MOISTURE

SPECIES — T / R SHRINKAGE, % OF GREEN

MOISTURE CONTENT (%)

UNITS

// enter the LOWEST moisture content the sheet reaches — normally the dryer outlet, not the layup. Shrinkage on first drying is not fully recovered when the sheet regains a few points on the way to the press. Softwood for phenolic glue, 5 % or under; hardwood for urea glue, 6–8 %; face veneer, 8–10 % (Lutz).

DRY TARGETS — WHAT THE SHEET MUST MEASURE AFTER DRYING

THICKNESS (IN, FRACTION OR THOU)

LENGTH — ALONG THE GRAIN (IN)

WIDTH — ACROSS THE GRAIN (IN)

// any one is enough. Width is the clip width — what the continuous peel is cut to — so enter the dry width the sheet has to measure and the clipper setting comes back. In inches, a bare thickness of 1 or more reads as thousandths: 100 is 0.100 in.

ALLOWANCES — ADDED AFTER SHRINKAGE

GREEN PEEL THICKNESS (IN)

// peeling variation and nosebar compression beyond the knife (Briggs; Lutz). Sanding, if the panel line sands, is on top of this

SCORE LENGTH (IN)

// end trim and spur allowance — the middle of the 100–104 in lathe length Briggs records for a 96 in panel

CLIP WIDTH (IN)

// panel squaring and the sheets that shrink more than average — chosen so a 48 in target reproduces the industry's 54 in clip

// these three are the tool's defaults, not a measurement of any mill. Overwrite them with yours and the link carries them.

CHECK A GREEN SETTING — OPTIONAL

GREEN PEEL THICKNESS AS SET (IN)

SCORE LENGTH AS SET (IN)

CLIP WIDTH AS SET (IN)

// the inverse question: what does a setting you already run dry down to? A dry target on the same axis takes precedence.

ADVANCED — DRYING FACTORS, LONGITUDINAL SHRINKAGE, FIBER SATURATION

WIDTH FACTOR

THICKNESS FACTOR

LONGITUDINAL S₀ (%)

FIBER SATURATION (%)

// the factors multiply the book shrinkage. Table 4-3 describes small clear pieces drying slowly; veneer in a hot dryer shrinks LESS in width (Lutz: yellow-poplar 6 % at 150 °F, 4½ % at 350 °F, against 6.8 % from the book) and MORE in thickness. Hot dryers typically land between 0.7 and 0.9 of book on width. The only way to know your number is to measure it. Longitudinal shrinkage is 0.1–0.2 % for normal wood; the handbook has no per-species column for it.

ASSUMPTIONS // what the numbers rest on

// shrinkage begins at the fiber saturation point and is linear with moisture content below it (Wood Handbook eq. 4-9). Table 4-3 values are percent of the GREEN dimension, so green = dry ÷ (1 − S).

// a rotary sheet is flat-grain everywhere: width shrinks tangentially, thickness radially, length along the grain.

// the book describes small clear pieces drying slowly. Hot dryers shrink veneer less in width and more in thickness; the coefficient of variation between sheets is about 15 %. Predicting one sheet is impossible; predicting the average of many is not.

// sources: USDA FPL Wood Handbook FPL-GTR-282 (2021) ch. 4; Lutz, Techniques for peeling, slicing, and drying veneer, FPL RP-228 (1974); Briggs, Forest Products Measurements and Conversion Factors, ch. 5.

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