How to use an aerial 36 inches lens

after two passes on the A side, first pass ont the side B.

as you can see, there's a deviation of the line, I was pushing too hard and the vise holding plate of the drill has turned instead of the aluminium plate I was machining.

As it's the first pass, it's not very important, but from then, I had to hold the base plate with the left hand while turning the aluminium plate with the right one.

a larger view of the system. 

That creepy drill was brought on a garage sale for only 20 €, there was no more on/off switch (fond in another garage sale) but the tool holding mandrel is very stiff and has no perceptible axial movement.

Using my little bench drill as a router, with an 2 mm tool, and a very small depth.

The size of the drill is just big enough to allow the plate to turn on it's central hole.

It's very long !

Drilling the central hole

Very hard 3 mm thick aluminium plate

changing the old plywood lens board is my first step