JD's Garage Micro
Draw and Cut Out Transition Template
The first thing I did was to draw and cut out an outline for my ramp's transition pieces which would become my template for tracing the rest of the side pieces I'd actually be assembling. Using the same template (which is used as a template only and does not become part of the finished ramp) for tracing all side pieces is a good idea because it ensures that all of the transition cuts for your ramp match as identically as possible. Attempting to draw your transition using the string and compass method for every cut would likely produce less consistent results. This initial template took four things into consideration.
1. The desired transition or steepness of my ramp 2. The size of my coping to know how far to cut in at what would become the "lip" 3. The height of my ramp 3. The size of my platforms
To draw the transition, I used the string and compass method with a 6' radius. This makes for a more mellow transition which I like. I experimented with drawing 5' to 6 1/2' transitions before cutting out my template side piece (which I used for tracing the 8 side pieces I actually used in the ramp), but 6' looked like about what I wanted. 5 1/2' - 6 1/2' is a good radius range for mini ramps, but I don't personally recommend using less than 6' because below that it gets a little steep for most people's tastes. The string and compass method of drawing your transition is more complicated to explain than it is to actually accomplish once you understand it. Here's how I did it.
First I placed one of my 4'x8' pieces of 3/4" plywood flat on the ground in front of me. I then placed an extra piece of wood scrap I had above it (you could just as easily use one of your other 3/4" sheets of plywood to do the same). My only criteria for the wood scrap I chose to use was that it was large enough for me to create a homemade compass with a 6' string length to draw my transition.
Starting on the outside bottom edge of the plywood (the left bottom edge in the above photo), I decided where I wanted my transition to start and marked that spot. If you'll be building a flat bottom of 2x4s, you'll generally want to start the transition 3 1/2" from the bottom edge of the plywood to allow for the size of the supporting 2x4's of the flat bottom In case that sounds confusing, 2x4's actually measure ~1 1/2" x ~3 1/2" rather than 2" x 4" as one might assume. That's where I get the 3 1/2" from.
(As a side note, if you were building a quarter pipe, the transition would start at the bottom edge of the ply because rather than meeting an elevated flat bottom, it would transition directly to the ground.)
From this point (the point 3 1/2" inches up from the bottom that I wanted my transition to start), I measured 6' straight up and hammered a nail in. I then tied a piece of string to the nail, measured 6' feet of string from that point, and tied a pencil to the end of the string. This results in a homemade compass which, when pulled tight, causes the upright pencil to fall directly on the point where my transition would start. Keeping the string tight and free of slack, I used this large compass to draw a curve from the starting point of the transition to the desired height of the ramp. My ramp was going to be 2 1/2' so I stopped drawing my transition when I hit 2 1/2" up from the bottom of the plywood I was drawing on.
You may notice from the above photo that I have drawn several lines on the plywood and there are actually 3 pieces of string visible - one that the pencil is tied to and two in the upper left portion of the photo going off to the side. This is because I was experimenting with drawing slightly different transitions and heights to see how they looked before deciding on my final outline. I encourage you to do the same until you're comfortable with what you're going to make your template. You'll have a better idea of exactly what I ended up deciding on by viewing the photo of what I cut out below.
Once you have the transition drawn, decide if you need to make additional cuts to accommodate your coping. I recommend using coping that is a diameter of 1 1/2" - 2 3/8". For my ramp, I chose to use coping that measured 1 5/8" in diameter. For a coping of 1 5/8" I had to make a cut that measured 1" down from the height of my ramp, and 1 1/2" back from the transitioned surface.
To draw my platforms, I then measured 24" from the coping notch away from my transition towards what would become the back of my ramp. I then cut out the entire outline which resulted in the following template piece.