How Much Will a 36 Inch Glued Up Walnut Panel Move
+0.5616" (+14.3 mm)
- Species: Black Walnut (tangential shrinkage 7.8%)
- Starting width: 36"
- Moisture content: 6% -> 12% (a typical dry-to-humid seasonal swing)
MethodΔD = D x ΔMC x (shrinkage% / 30 / 100)
Your actual humidity swing may be smaller or larger than the 6-12% MC example used here — run your own numbers in the movement calculator.
A 36" wide glued-up black walnut panel will grow about +0.5616" (+14.3 mm) across its total width moving from 6% to 12% moisture content — over half an inch, on a panel wide enough that most makers assemble it from four or five narrower boards rather than trying to source one solid 36" board.
Why this one specifically
Gluing several narrower boards into one wide panel doesn't change the total movement figure — the combined panel still moves as though it were one 36"-wide piece of solid walnut, because the individual glue lines don't restrain cross-grain movement any more than the wood fibres themselves do. What multi-board glue-ups do change is where that movement concentrates: a panel built from mismatched boards with grain running in different directions, or from boards of noticeably different moisture content at glue-up time, can cup or twist unevenly even though the total width change matches this figure.
What moves the number
Species is the biggest lever at this width — the same 36" panel in white oak would move closer to three-quarters of an inch, while mahogany at the same width would move just under three-tenths of an inch, still noticeably less than walnut but not the dramatic drop its 12" figure might suggest. Matching all the component boards' moisture content before glue-up, and orienting their growth rings consistently, reduces the risk of uneven movement without changing the total figure itself.