In frame-and-panel construction, the solid-wood panel sits unglued in a groove cut around the inside of the frame, so the panel can expand and contract every season without cracking itself or racking the frame. The groove must be deep enough to keep at least 1/4 inch of the panel's edge engaged when the panel is at its driest [2].
Why the panel floats
Worked example: an 18-inch flat-sawn white oak panel moves about 0.27 inch across its width through a 4% seasonal moisture content swing [1].
Worked example: the same 18-inch flat-sawn white oak panel moves about 0.41 inch through a 6% seasonal swing, which is the 4% figure multiplied by 1.5 [1].
A solid-wood panel glued into a fixed case cannot move, and something gives: the panel cracks, a joint opens, or the case racks.
A frame-and-panel panel is captured but not constrained. The groove holds the panel in the frame, and the panel moves freely inside the groove [3].
The frame provides the structure of a frame-and-panel assembly and the panel provides the surface. The panel edges are never glued.
Groove depth: the minimum
At the panel's driest seasonal point, at least 1/4 inch of each panel edge must remain in the groove [2].
Minimum groove depth = the panel's seasonal movement on one side + 1/4 inch of engagement [2].
Worked example: an 18-inch flat-sawn white oak panel at a 4% swing moves about 0.27 inch in total, about 0.14 inch on each side, so the groove needs to be at least about 0.39 inch deep [1][2].
Groove depth: the maximum
A groove that is too deep invites trouble during frame assembly: glue squeeze-out can bridge the gap between the groove floor and the panel edge and lock the panel in place [2].
A 1/2-inch-deep groove covers panels up to about 20 inches wide in white oak, walnut and cherry at a managed-shop swing of about 4% [2].
Panels wider than about 20 inches, and panels going into a swing of 6% or more, need the groove depth calculated rather than taken from a default [2].
Center gluing
A floating panel can drift seasonally toward one side of its frame until it bottoms out in the groove. A center glue spot anchors the panel at its midpoint so it expands and contracts equally in both directions [4].
A frame-and-panel center glue spot is a pea-sized touch of glue at the exact center of the top rail groove and the exact center of the bottom rail groove [4].
The stile grooves of a frame-and-panel assembly are never glued. The panel moves across its grain toward the stiles, and glue in a stile groove is a common way to crack a panel [4].
Center gluing is optional on panels up to about 16 inches wide in a managed shop, and recommended on panels wider than 16 inches [4].
Raised or flat panel
A raised panel has a field at full thickness and a thinner tongue that enters the groove. The shoulder between field and tongue casts a shadow line around the perimeter, and the profile is cut on a router table or with a dedicated plane.
A flat panel enters the groove at full or near-full thickness, with no shoulder [3].
The seasonal movement calculation is the same for raised and flat panels and uses the full panel width [3].
Three checks on a frame-and-panel plan
Many plans default to a 3/8-inch groove depth, which is marginal on wide panels. Check the plan's groove depth against the panel width and moisture swing before cutting [2].
A plan that says nothing about gluing the panel means the panel is not glued. Silence in a plan does not mean glue.
A frame-and-panel piece leaving the shop for a different climate is designed with the wider service-environment swing: about 4% for a managed shop and 6% as the default for an unmanaged home [5].
A frame-and-panel panel that shifts slightly in its groove when the air cools is working as designed.
Sources
- USDA Forest Products Laboratory, Wood Handbook (FPL-GTR-282), Chapter 13, Equation 13-3 and Table 13-5, dimensional change coefficients, with the corrected 4% table and the multiply-by-1.5 rule for a 6% swing (as listed in Hewn's notes, entries HEU-R735 and HEU-R739).
- Hewn heuristic entry HEU-R750, frame-and-panel groove depth, 2026-03-15, Hewn internal, unreviewed.
- Hewn heuristic entries HEU-R749 and HEU-R752, frame-and-panel system and raised vs. flat panels, 2026-03-15, Hewn internal, unreviewed.
- Hewn heuristic entry HEU-R751, frame-and-panel center-glue protocol, 2026-03-15, Hewn internal, unreviewed.
- Hewn heuristic entry HEU-R736, moisture content swing by environment, 2026-03-15, Hewn internal, unreviewed.