You will need approximately 4 2 in × 4 in (5.1 cm × 10.2 cm) planks about 8 ft (2.4 m) long. This will be enough to create 2 A-frame. Use a miter saw set at a 22.5 degree angle. Wear safety goggles, ear muffs, and a dust mask if you cut the boards yourself. You can also rent a saw at a home improvement store or have store employees cut the following boards:  2 planks 18 in (46 cm) long. 2 planks 20 3⁄4 in (53 cm) long. 4 planks 36 in (91 cm) long. 2 planks 37 7⁄8 in (96 cm) long. Set the boards out on a flat surface so you can fasten them together. Work on 1 A-frame at a time. To create the frame, place the 2 medium boards on the sides. Fit the remaining boards between these medium boards. Place 1 of the long boards at the bottom, then fit the shorter boards at the top and in the middle. Each A-frame uses 5 boards. When you’re done, the boards will create the shape of an A. Make sure all of the boards fit snugly together. Countersinking pilot holes prevents the boards from cracking and weakening. Use a drill with a 3⁄4 in (1.9 cm) countersink bit to drill a pair of holes in each of the middle boards. Measure about 2 in (5.1 cm) from the ends of each board, then drill the holes diagonally into the side boards.  Work from the bottom edges of lower support boards in the middle of the A-frame. For the small board at the top, drill through the side boards to reach it. Use a pair of wood clamps to hold the boards in place as you work. Place a screw in each of the pilot holes. The screws will pass through the support planks and into the frame planks on the side. Make sure the boards fit together well and feel sturdy when you try to move them. That way, they won’t fall apart when you’re walking on your slackline. The plywood creates a spot for you to attach the slackline and anchor lines. You will need a 8 in (20 cm) sheet of plywood 1⁄2 in (1.3 cm) thick for each A-frame you wish to make. Set the A-frame on top of the plywood, then trace its outline with a pencil. Cut the outline using a reciprocating saw.  You can also use a jigsaw or circular saw to cut the plywood. To avoid cutting the plywood too short, leave it a little longer than the outline. You can always cut it down further or sand it, but you can’t fix it once it’s too small for the A-frame. Place the plywood over the A-frame. Place a screw about every 12 in (30 cm) along each of the boards in the frame. Screw through the plywood and into the frame boards to secure everything together. The frame boards are a little difficult to find underneath the plywood. Feel for the solid boards through the plywood. If you’re unsure, lift up the plywood to locate them. Outline them with a pencil to help you place the screws. Use a 1 1⁄2 in (3.8 cm) drill bit to make the holes. Position them underneath the top board on the A-frame. Make the holes about 2 in (5.1 cm) apart. Use a reciprocating saw or another tool to remove the wood between the holes. Basically, you create a slot in the A-frame to thread the slackline webbing through. Find an anchor point for each A-frame. One way to do this is by planting metal stakes or struts firmly in the ground. Use extra line lockers and carabiners to run the webbing from the stakes to the slot in the A-frame. Make sure the stakes are well-planted so the frames can’t move when you touch them.  Another way to plant the A-frames is by burying concrete cinder blocks in your yard. Tie a chain around each cinder blocks, then run the chains to the A-frames. To preserve the webbing for longer, sand your A-frames smooth before using them.

Summary:
Cut wood boards to create the A-frame components. Arrange the boards in an A-shape on a workbench. Clamp the boards and drill pilot holes through them. Bolt the boards together with 2 1⁄2 in (6.4 cm) decking screws. Cut plywood to fit over the A-frame. Fasten the plywood to the A-frame with 2 in (5.1 cm) decking screws. Drill a pair of holes through the plywood to create anchor points. Tie the A-frames to anchor points using nylon webbing.