It's going to be 5 mm thick Dibond, a drop from picture laminating, 600 x 190 mm, its lighter than metal, rigid and flat. The size of the lens has been traced but it'll have a square opening.

Very easy to cut with a 2 mm tool, but not at a too fast speed, I don't want to have the smell of burned PVC in my workshop.

Doesn't go straight very easily, needs clamping.

I really love using those metal parallel jaws clamps, they're very strong, not always very fast to adjust ((when you have the screws on top of the left one, it takes time to go down !), but very strong.

Ok, it fits perfectly, but the 1 centimeter left on each sides of the opening are not enough to make it strong and flat for a long time : it must be reinforced.

That complicated double H aluminium profile will be perfect when cleaned of that strong double sided adhesive tape (it had been used behind some pictures, laminated on Dibond, to strengthen the flatness... and it's going to have exactly the same purpose, on the same material, when recycled.

And please stop crying and screaming, this wood chisel has been found in the street, just out the door, and the blade was quite worn, and I have another one which has the same width and a good Swedish blade, so after a little sharpening, it's very useful for that kind of heavy duty work.

But first, a small sliding rig must be build.

so it can be cut in two halves, in the middle.

Same 2 mm tool, the fastest possible speed on the drill (around 2500 RPM only), and patience, but patience is a skill a photographer must excel at, we're experts in time.

Nearly finished ! It took some time though.

Good, but now it's too thick ! those 2 millimeters added to the Dibond  where not in the program, and it will no more slide.

So the Dibond has been routed, to have the exact thickness needed for the blade to slide.

Gluing with Araldite epoxy and a heavy weight to hold in place. 

And... it fits perfectly, tight, much too tight, it does not slip easily at all. The H profile has an 5 mm opening, the rack profile has a 5 mm thickness, and the adjustment is in a too high number on the tolerance scale, it won't work like that !

Trying to get some space with the help of fine grain sand paper.

A lot of dust but...

Too tight ! I have to find another solution for the still part of the mechanism as the blade is very satisfying.

Here nearly finished with the moving blind...

Once again too tight ! I had to use that little wood hammer to make it slide back... needs some sanding here too.