How to Cut Cupped Lumber

Cupped lumber can often be salvaged.

Cupped lumber is curved because one side of the wood shrinks faster than the other. This usually occurs when the ring pattern of the wood isn't symmetrical. To prevent cupping, place heavy weights on the lumber for three days while it is drying. Use 150 pounds for every square foot of lumber. If your dried lumber is cupped, making small cuts in it can help straighten it.

Things You'll Need

• Table saw
• Ruler
• Weights

Instructions

1. Find the direction of the cup in the lumber by looking at the end of the board. It may have a "U" shape.

2. Set the depth of your table saw to 1/2 inch. Place your piece of lumber on the saw, with the bottom of the "U" shape facing down.

3. Make a 1/2-inch-deep cut in the center of the lumber, running the length of the board. Move the wood left 1 inch from the center. Use the ruler to measure.

4. Repeat until you have made three cuts to the left of the lumber's center and three cuts to the right of the center.

5. Place the weights on top of the board and let them sit for three days. Remove the weights. The cuts and the weights will have straightened the wood without losing much lumber strength.

Tips & Warnings

• Wear protective goggles and gloves when using a table saw.

References

• University of Wisconsin Extension; Causes and Cures for Warp in Drying; Eugene M. Wengert, et al.
• HammerZone.com; Flattening a Cupped Board With Multiple Saw Cuts; Bruce W. Maki

Resources

• National Center for Wood Transportation Structures; Conventional Lumber ...; Primus V. Mtenga