Build a solar hot dog cooker

Step 2 Cut the sides to a parabolic profile

I designed my parabolic cooker with a focal distance F of 18 inches. Thus my formula was:
Y = X²/72 (where both X and Y are in inches).

I used a spreadsheet to calculate and plot the value of Y for all values of X from -24" to +24".
Y is the same whether X is positive or negative, so I've only shown Y values for X values from 0 to 24 here). Those values are:

X - Y
0 - 0.000
1 - 0.014
2 - 0.056
3 - 0.125
4 - 0.222
5 - 0.347
6 - 0.500
7 - 0.681
8 - 0.889
9 - 1.125
10 - 1.389
11 - 1.681
12 - 2.000
13 - 2.347
14 - 2.722
15 - 3.125
16 - 3.556
17 - 4.014
18 - 4.500
19 - 5.014
20 - 5.556
21 - 6.125
22 - 6.722
23 - 7.347
24 - 8.000

Draw a grid with 1" spacing on one of the 2 sheets of plywood to be used for the sides. similar to that shown below, and plot the curve. Then simply cut along the curve with a jig saw. You can repeat the process on the second sheet or use the first sheet as a template to trace the curve onto the second (or if you are a brave enough, you can attempt to cut them both at the same time... clamp them together well first).