Step 1: What you need
Saw (I suggest a circular table saw, for precise repeatable cuts)
cardboard for template.
some scrap wood.
baking paper (or anything else to separate wood while gluing).
belt sander (Use a fresh sanding belt!)
Sandpaper or sanding machine to sand concave forms
Step 2: Design phase
I had 2.3cm thick multiplex board, therefore I needed 16layers. each layer is made up of a frame of 4 pieces of multiplex strips (makes 60 strips + 1 baseplate).
I wanted a maximum wall thickness of about 2.5cm (as you remove quite a lot of material to round it, you should make the wall thickness about equal the board thickness).
So I had to cut strips of 2.5cm x 13.5cm. and a base plate of 16cm x 16cm.
As I wanted to have a half revelation each layer had to be rotated by about 11.2 degrees.
To easily measure this rotation while stacking up the layers I built a template of card board that had 2 crosses on it. The second cross is rotated by 11.2 degrees from the first one. I made short cuts in the end of the crosses. When i put the template on each frame and make marks on each frame i can easily align the marks and create a smooth revelation.
Step 3: Making the frames
I started off cutting all the equally sized strips of multiplex board and the base plate
Instead of gluing each frame after another, I built four tall brackets by screwing together 2 pieces of scrap wood in right angle to each other.
The next step of work has to be made pretty fast (before the glue can set).
Take four pieces of the multiplex-strips and glue them together to a frame.
Put small pieces of baking paper on the glue points, so that the layers you put on top of each other don’t stick together. Make three or four more layers and put them on top of each other (so that they form a straight tower). Now Put the brackets on the four corners of your small tower, and clamp them lightly together with four clamps. Keep adding layers to the end of your brackets (always take care, that your layers are nice and plane on the top).
Now add another four clamps at the top and clamp everything tightly together. You have to tighten the clamps equally, or your frames might start to move and become unsquare. It’s best to add a few more clamps in the middle of the brackets for some extra strength.
I Also put on some clamps on the sides, to keep the sides plane and even, see last images. (I didn't put on pressure equally enough on all sides...)
This step doesn't have to be ultra precise, you're gonna sand quite a lot anyway!
Step 4: Stacking it up
Mark all frames with your templates. Stack the frames on top of each other by aligning the marks. You should have a nice full revelation.
I marked the outline of each layer on the underlying layer, so that I knew where to put glue.
Now glue the tower together. after stacking them all up, I clamped them together by putting slightly larger boards on the top and bottom. If you don’t have long clamps you can also put heavy weights on top. let everything dry thoroughly.
Step 5: Sanding it up
At first I roughed down the edges, and then I smoothed everything down, to have a somewhat even surface. This step took me about 2 hours.
After that I used a smaller random orbital sander, to finish it up (not the best choice, but it was the only sander with a somewhat soft baseplate). I used up to 180 grit.