Well, actually I just completed 5 of them... after I put the first prototype holder through a couple of years of field experience to verify my design.

After I bought my new Canham and saw the $400 price tag for 8x20 holders, I decided to put my woodworking skills to use and make a few of my own holders. Using an ancient 8x20 Corona holder as a typical example, I came up with a design, cut parts for 6 holders, and assembled one of them for verification. It worked beautifully, but I just didn't have the time to finish the other 5 until I retired a few weeks ago.

If you're entertaining the idea of making your own holders, here are some of the things I encountered:

Accuracy cannot be taken for granted. One must work with precision measuring instruments typically used in metalworking. You can't measure to plus or minus 0.005" using a metal ruler.

A thickness planer capable of sizing wood to 0.005" is mighty handy. The router table must be FLAT, and you'll need a way to measure cutter depth to 0.005". You may even need to have cutters ground to specific sizes for slotting the siderails. I have small vertical milling machine which I used to machine intricate joints and the recesses for the light baffles.

At first, I experimented with Oak, but quickly recognized the wisdom of the ages, and used Cherry. Super stable, strong, it machines beautifully, and doesn't split. The parts for the last 5 holders were in storage for the past 3 years, and were just as straight and precise as the parts used for holder number one.

The hinge cloth is a bookbinders fabric which I tested for flexing and cracking. I made a sample hinge and submitted it to 2700 complete reversal (180 degree) bends, with no sign of pinholes thru the coating.

The darksides are "Garolite", a phenolic material, and the septums are 6061 aluminum, both from McMaster-Carr.

It's a complex project, now I understand why these things cost a much as they do...