Crown Molding
While curving molding is more difficult than applying a simple perpendicular mitre joint, it can be done. There are two methods for putting a curve in originally straight molding, kerf cutting and steam bending. Kerf cutting involves making a series of small slices in the molding to allow it to bend. Steam beaming involves building a small steamer, heating the wood with moisture, and then letting it cool on a jig made to your desired radius.
Instructions
Kerf Cutting
1. Measure the perimeter of the curve. Mark this length on your molding, so you know what distance your kerf lines need to cover.
2. Mark kerf lines on your molding. Using a pencil, place a mark every inch along the portion of the molding you need to bend. For external corners, make your marks on the back of the molding, and for internal corners, make your marks on the front of the wood.
3. Set your table or radial saw to slice the wood with one-sixteenth of an inch remaining. At this thickness, the wood should be easy to bend.
4. Make your cuts moving every inch along the wood and making your slices. When finished, the front or back of the wood (depending on corner you need to round) will look "ribbed" in appearance.
5. Place wood glue inside the notches you made and bend the wood to your desired circumference. Place clamps on the wood to hold it in place until the glue thoroughly dries.
Steam Bending
6. Build a steam box by taking a piece of PVC pipe large enough to fit your molding, and cut to a length roughly 6 inches longer than the length of molding you wish to steam.
7. Glue an end cap to one end of the PVC pipe and drill a hole approximately one-quarter of an inch into the end cap. This allows the steam to escape.
8. Drill another hole toward the front of your PVC steam chamber. Insert your steam pipe from your steamer into this hole, and make sure it has a good fit.
9. Place your molding inside the PVC steam chamber and cap the other end. Turn on your steamer and allow the wood to steam. As a general rule, provide one hour of steaming per inch of thickness of the lumber to make it pliable enough to bend.
10. Put on heat-resistant, heavy duty gloves and use tongs to remove the molding from the steam chamber when the steaming process is complete. Be careful, the wood is very hot at this point.
11. Place your molding over a plywood jig cut to match the curvature of your corners. Clamp the molding to the jig and allow the molding to cool and dry.
12. Unclamp the molding when it is cool. When you remove the molding, it will be the shape of the jig you clamped it to. You can now install your molding in a curve.
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