Careful scribing, a thoughtful process, and a couple of third-hands make multiple-segment faux beams "look like they grew there."
Use a laser to layout and install blocking on the ceiling with framing lumber. Matt rips 2x4s in half and makes 'ladder panels' which are lightweight and solid. The ladder panels are screwed into the ceiling framing with structural screws.
Rip a slight bevel on the bottom edge of the ladder backing to make slipping the beam into place easier.
Use a scribe offset block for consistent marks across multiple beams to align all joints. Installing the first segment of a beam on this line (which is two inches from its final spot means you can use the scribe offset block to scribe the end of the beam to fit the tape and joint compound buildup on the wall.
Cut the line with a sharp, finely toothed blade. Cut a little proud of the line and use a belt sander to close in on the exact cut. Begin the sanding with a slight back-bevel. This allows you to close in on the pencil line from a thin sliver of wood rather than a 3/4 inch hunk of board.
Install the first segment of beam tight to the wall and bask in the wonderfulness of the fit.
Use trim screws, slightly countersunk, to attach the beam to the blocking. Place the screws near the ladder blocks. Countersinking the screws avoids slight mushrooming in the wood.
Place the tools where you'll need them when you're holding the next beam section over your head.
Position the next segment and mark the leading end of the beam with a pencil. This mark will help align the third beam section so that you can scribe it to the opposing wall.
Take the second beam section down.
Use the two-inch offset block to mark another scribe-guide line.
Scribe the end of the beam. Be careful to follow the topography of the wall to make sure the scribe line and cut will fit tightly to the wall.
This second scribe yields a section that is slightly too long (exactly one skosch!). Rather than cut the square end of the beam, or cut either end of the center section, Matt uses a 6-inch putty knife as a scribe guide to remove 1/32-inch or so.
Use a belt sander to remove the extra skosch.
Test-fit the beam again and screw in place.
Slide the center section into place and screw into the ladder backing.
With all twelve beams fitting, Matt takes them all down and trucks them to his shop for faux finishing.
—Matt Jackson is a master carpenter, remodeler, SketchUp Wiz, YouTuber, and contributing editor to ProTradeCraft. He lives and works in Rapid City, South Dakota.