How to Build a Sofa Box Frame

When you can't find the right sofa to create the look you desire, build your own. Although the height, shape and angle of the back and arms creates the overall look, a well-built sofa starts with a simple box frame. Once you build the sofa box frame, choose a height, shape and angle for the back and arms. Springs and padding provide the support you need for maximum comfort and durability, while the upholstery finishes the look.

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Most sofas start with a simple, box-frame base.

Butt-Joined Sofa Box Frame

Step 1

Lay two of the 71-inch-long pieces of 2-by-2-inch stock lumber on a flat surface, 20 inches apart.

Step 2

Place two of the 20-inch-long pieces of 2-by-2-inch stock lumber between them, with all corners flush, creating a 71-by-24-inch rectangular frame.

Step 3

Place a 24-inch bar clamp across the width of the rectangle, 6 inches from each end of the long boards, to hold the frame together while you drill the screw holes.

Step 4

Face one of the 71-inch sides. Drill 1/8-inch diameter pilot holes through the side, into the 20-inch rails, at the center point of each rail. Countersink all the holes.

Step 5

Secure the 71-inch sides to the 20-inch rails using 3-inch-long, 1/4-inch-diameter wood screws.

Step 6

Repeat all previous steps to build a second 71-by-24-inch frame.

Step 7

Have helpers hold the two frames on their 1/2-inch edges, 19 inches apart. Place 19-inch spacer rails between the two frames, even with each 24-inch rail.

Step 8

Place a 24-inch bar clamp across the span between the two frames, 6 inches from the top and bottom, at each end of the frame.

Step 9

Drill 1/8-inch-diameter pilot holes through the frames into the 19-inch spacer rails. Countersink all the holes. Secure the rails to the frames using 1/4-inch-diameter, 3-inch-long wood screws.

Step 10

Have a helper hold one of the 24-by-24-inch plywood sheets against one of the short sides of the frame. Drill pilot holes as previously described, every four inches, through the plywood and into the frame. Attach the 24-by-24-inch sides to the frame, using 1/4-inch-diameter, 1.5-inch-long wood screws.

Step 11

Lay the 1/2-by-24-by-72-inch plywood sheet on top of the frame. Drill pilot holes every 4 inches, one inch from the outside edge, along all four sides of the plywood. Countersink the holes and attach the plywood to the frame using 1.5-inch-long wood screws.

Step 12

Lay one piece of 48-inch-long stock lumber on its 4-inch face. Snap a chalk line across the board 24 inches from one end, on its 4-inch face. Mark one end of that line "A" and the other end "B."

Step 13

With point "B" facing you, label the closest corner of the left end of the board point "C." Label the farther corner of the left end of the board point "D." Make sure that the four labeled points read "A" at the center point that is facing away from you, "B" at the center point that is facing you, "C" at the first corner at the left end of the board, and "D" at the remaining corner of the left end of the board.

Step 14

Repeat to label all five boards. Miter the boards from point B to point D to create sofa back braces.

Step 15

Face one of the 72-inch sides of the base of the sofa box frame.

Step 16

Place a sofa back brace against the sofa box frame base, with the angled side facing away from you, even with one of the 24-inch rails in the sofa base.

Step 17

Drill 1/8-inch diameter pilot holes through the brace and into the rail, every four inches. countersink the holes and secure the brace to the rail using 1/4-inch-diameter, 6-inch-long wood screws.

Step 18

Repeat to attach all of the back braces.

Step 19

Lay the 3/8-inch plywood sheet across the back braces. Drill and countersink 1/8-inch pilot holes along each brace, every four inches. Secure the plywood to the braces using 1.5-inch wood screws.

Step 20

Pad and upholster the couch as desired.

Mortise-and-Tenon Box Frame

Step 21

Substitute 2-by-4-by-22-inch-long spacer rails for the 2-by-2-by-19-inch rails used to make the butt-joined sofa box frame.

Step 22

Lay one of the 22-inch-long spacer rails on your work surface on one of its 2-inch faces. Mark the 4-inch face that is facing you "A." Mark the one facing away from you "B." Mark the 2-inch faces "C" and "D." Mark the ends of the board "E."

Step 23

Set a tenon gauge 1-inch deep. Place the gauge against side E and scribe the shoulder depth of the tenon on the wood, at each end of each rail, on sides A through D. Lay a carpenter's square against the scribe marks and trace over each one with a carpenter's pencil to connect them on all four faces.

Step 24

Set the tenon-marking gauge to 1/2-inch. Place the gauge against one end of side A on the 22-inch-long rail and scribe a line in the wood on side C, 1 inch long. Place the tenon gauge against side B and repeat.

Step 25

Place the gauge against one end of side A on the 22-inch-long rail and scribe a line in the wood on side D, 1 inch long. Place the tenon gauge against side B and repeat.

Step 26

Turn the rail around and repeat the same marks at the other end. Repeat for all 10 rails.

Step 27

Face side E at one end of the rail. Place the tenon gauge against side C and mark the shoulder depth of the tenon, from side A to side B at both ends of the rail. Repeat for all 10 rails.

Step 28

Face side E at one end of the rail. Place the tenon gauge against side D and mark the shoulder depth of the tenon, from side A to side B at both ends of the rail. Repeat for all 10 rails.

Step 29

Secure each rail in a bench vise and cut along the tenon lines from side A to side B, into side E, 1-inch deep, using a dovetail saw.

Step 30

Turn the rails in the vise so that side A is up. Cut into side A 1/2-inch deep and remove the waste to create the first cheek of the tenon. Cut into side B 1/2-inch deep and remove the waste to create the second cheek. Repeat for all 10 rails.

Step 31

Turn the rails in the vise so that side C is up. Cut into side C 1/2-inch deep and remove the waste to create the first shoulder of the tenon. Cut into side D 1/2-inch deep and remove the waste to create the second shoulder. Repeat for all 10 rails.

Step 32

Use a router to cut 1-inch-wide mortises, 1-inch-deep by 2-inch-long, into the front and back frames, 1 inch from each end of the 24-inch-long rails.

Step 33

Apply carpenter's glue to all surfaces of each tenon and to the inside of each mortise, using a 1-inch paintbrush.

Step 34

Insert the tenons into the mortises. Place a 24-inch bar clamp across the span between the two frames, 6 inches from the top and bottom, at each end of the frame.

Step 35

Allow the glue joints to dry overnight. Continue assembling the sofa box frame at Step 10 of the directions for the butt-joined frame.