"Picture with developers looks much smaller than dimensions given - is this a model? I would imagine you would want the blades high enough to avoid risk of hitting people or animals which might stray beneath them. What sort of noise would this produce? "
"I am no engineer but surely an arch depends on compression forces. Half an arch, as in the shelf supports, is not using compression so loads would tend to pull the joints apart rather than push then together, as in a full arch. So those face grain to end grain joints are going to rely entirely on the strength of the glue! "