Strip thickness · Strip count · Form radius with springback · Board-feet & glue area
How thin you cut strips for bent lamination depends on the bend radius and the stiffness of your wood species. Thicker strips spring back more and may crack on tight curves; thinner strips bend easily but mean more resawing, more glue lines, and more clamping time.
The guidelines below come from American Woodworker magazine, widely cited across woodworking forums, and assume medium-stiffness hardwoods (cherry, walnut). Adjust thinner for stiff species (maple, oak, ash) and you can go slightly thicker for very compliant softwoods (pine, poplar).
| Inside Radius | Recommended Strip Thickness | Note |
|---|---|---|
| 2–4″ (51–102 mm) | 3/32″ (2.4 mm) | Very tight; use thinnest possible strips |
| 4–8″ (102–203 mm) | 1/8″ (3.2 mm) | Common for chair legs, curved aprons |
| 8–12″ (203–305 mm) | 3/16″ (4.8 mm) | Moderate curves, cabinet sides |
| > 12″ (> 305 mm) | 1/4″ (6.4 mm) | Gentle curves; can often use thicker stock |
Source: American Woodworker magazine, strip thickness guidelines for bent lamination, widely cited on SawdustZone, Sawmill Creek, WoodWeb forums.
Bent laminations spring back toward a larger radius when removed from the form. You must build the form tighter than your desired finished radius. Two formulas are in common use:
R_form = R_final × (n − 1) / nn = number of plies, R_final = desired finished radius.
y = x / n²x = form deflection (arc height from chord to apex) and y = springback amount.
Both formulas are approximations — actual springback varies with species, glue type, cure time, humidity, and strip thickness. The deflection formula assumes y is small relative to the arc. For best results, always do a test lamination on scrap and measure actual springback before committing your final stock.
Using rigid, non-creeping glue (urea formaldehyde / plastic resin glue, or epoxy) significantly reduces springback versus standard PVA. Leaving the lamination clamped on the form for 24 hours (vs. 1–2 hours minimum) also helps.
Strip count = finished thickness ÷ strip thickness, rounded up. For example: 3/4″ finished thickness at 1/8″ strips = 6 strips. More plies mean less springback (springback is inversely proportional to n²), more glue lines, and more resaw time. Aim for at least 6–8 plies on curves tighter than 8″ radius. With 4 or fewer plies, springback can be significant.
Each rip cut through your board loses a kerf width of material. If your board is 1.5″ thick, strip thickness is 1/8″, and kerf is 1/8″, each strip + kerf = 1/4″, so you get 6 strips per board-run (1.5 ÷ 0.25 = 6). Make strips 2–3″ longer than the arc length on each end for clamping and trimming.
Goal: A rocking chair rocker. Final inside radius 10″, 90° arc, 2″ wide, 3/4″ thick, walnut (medium).
Build the form to an inside radius of ~8.33″, glue up 6 walnut strips with extended-open-time glue, and expect the finished rocker to arrive at ~10″ inside radius.
Strip thickness depends on the bend radius and wood species. A commonly used guideline: for a 2–4″ radius use 3/32″; 4–8″ use 1/8″; 8–12″ use 3/16″; over 12″ use 1/4″. Stiffer species (maple, oak) need thinner strips than cooperative ones (cherry, walnut, pine). Always test on scrap first — these are starting points, not guarantees.
Use the formula: R_form = R_final × (n − 1) / n, where R_final is the radius you want after springback and n is the number of plies. With more plies, the form radius gets closer to the desired final radius. For 10 plies and a 10″ desired radius, the form radius = 10 × 9/10 = 9.0″.
Springback deflection (the arc rising) can be estimated by y = x / n², where x is the arc's deflection on the form (height from chord to apex) and n is the number of laminations. More plies dramatically reduce springback: going from 4 to 8 plies cuts springback by a factor of 4. Rigid glues (epoxy, urea formaldehyde) and full cure time on the form also minimize springback.
Divide finished thickness by strip thickness, rounding up: e.g. 3/4″ thick at 1/8″ strips = 6 strips. More strips = less springback but more glue joints. Aim for at least 6–8 plies on curves under 8″ radius for manageable springback.
Urea formaldehyde (plastic resin glue, sold as powder) or epoxy give the least springback and resist creep under sustained stress. Titebond Extend (extended open time PVA) is popular for its long working time (needed when spreading glue across many strips). Standard Titebond I/II can creep over time on curved parts under load, so it's less ideal for structural bent laminations.
Often yes. A solid curved part bandsawn from flat stock always has short-grain sections where the curve crosses the grain direction — a structural weak point. A properly glued bent lamination runs long grain along the full arc with no short grain, and the face-grain-to-face-grain glue joints are among the strongest joint geometries in woodworking. The finished part can be stronger than an equivalent solid-wood piece.