Step 1 - Cut the Sides
- 2 pieces 3/4" untreated plywood
- Pencil
- Jig Saw
- Ruler
I describe the string and compass method fully here, but you might also want to check out the more general String and Compass Help.
First, Draw a point that is 12" into the length and 3.5" into the width of one of the 4' x 8' sheets of plywood.
Next, screw a 2x4 into the plywood so that the inside edge is 12" into the plywood.
Put a screw into the 2x4 that is 6' 10" away from your starting point. 6' 10" is the transition radius, If you want your ramp to be steeper, decrease this length (a transition radius of under 3.5 feet would result in your ramp having vert). You can use the ramp tool to preview the plywood cut if you make adjustments.
Tie a string to this screw, tie a pencil to the other end of the string so that the pencil will be on the starting point when the string is taught. Make sure to use a rope or string that does not have much give, fishing line works well.
Now it is time to draw the transition. Make sure you take your time with this, and that you keep the pencil vertical as you draw.
Once you have drawn the transition (only draw one), cut it out with a jig saw.
After cutting the first piece, lay it on the remaining plywood to sketch another transition, cut this out as well.
Note that I am only taking pictures of building one side of the halfpipe, use your first cut to sketch two more pieces out of the other 3/4" sheet of plywood.