Step 4 - Platform Skeleton
Materials required: 7 pieces of treated 8' 2x6, 4 pieces of treated 8' 4x4, 2 pieces of treated 8' 2x8, 5 pieces of treated 8' 2x4s
Just like the height of the halfpipe, the size of the platform can be adjusted. In the halfpipe pictured we made the platform about 30". We probably would have made it bigger but the owner wanted the halfpipe to be as hidden as possible. However, by making the platform 30" long we were able to get 3 cuts out of each 8' 2x6 so it saves some wood. Another popular length might be around 4', which would be two pieces from each 8' 2x6.
For the 30" platform, use 6 pieces of treated 8' 2x6s to cut 18 pieces that are 30" long. Screw two into the side pieces made in step 2. Screw them into the 2x8 at the top of the side piece.
Next cut the treated 2x8 to 8' and screw it into the back of the 30" 2x6s you just tied in. The 2x8 will stick out 3/4" on each side of the 2x6s since they are screwed into the inside of the plywood sides.
Now take an 8' 4x4 and stand it vertically inside the corner made by the 2x6 and 2x8 you just screwed in. Use a level to make sure that the 4x4 is straight up and down. Dig a spot for a concrete block to go where the 4x4 hits the ground and place the 4x4 on top and screw it into the 2x6 and 2x8.
Next make a mark every foot on both the outside and inside 2x8, there should be 7 marks on each side. Take the remaining 14 pieces of 30" treated 2x6s and screw them in at the marks you made.
Now you need to add extra supports under the platform. Cut a piece of treated 2x4 to 8 feet. Place one at the bottom behind the 4x4s and screw that in. Next cut a 2x6 to the hight of the halfpipe from the cement block to the top and screw it into the side. Cut another 2x4 to about 35" (5" longer than however big you made your platform). Screw this piece at the bottom to the outside of the 4x4 and inside of the vertical 2x6 you just tied in. Finally cut a 2x4 to 7' 10.5" and screw it in on top of the 2x4 you just put in. This whole support part is a little hard to put into words but the pictures below should clearify everything.
Thats it for step 4, your platform should look something like this.