You will be holding the mirrors in place by washers sandwiched in between two nuts. This is tedious. You will begin by putting together a spreadsheet or other calculation to tell you how many mm each mirror corner should be offset from its neighbors. The basic formula for this is the formula for a parabola
. This is a parabola in 2 dimensions, however, so it's a little more complicated than that. Really, the formula is z=1/(4*f)d2
) and f is the focal distance of the device. I chose a 72 inch focus. Don't do anything different unless you understand why you're doing it. Let me recommend that you study the math and don't try to align the mirrors by hand. It's even more difficult than measuring it and the focus isn't as good.
What happens is that when you get past the 3rd row out from the center is that your distance up each screw starts to get bigger than the screw is long. This is not really a problem. The trick is to offset all sides of a given mirror so that the lowest edge is as low as you can make it. What you get is rows of mirrors at the same angle, but not in the same plane. This is similar to a fresnel lens for those who understand optics.
If all of this is lost on you, I have attached a screenshot of the spreadsheet. This is a list of the mirror offsets for each of the mirrors as measured in millimeters. This will give you a focal distance of 72 inches. It works fairly well.