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Hi Massimo, thank you very much for the exhaustive and valuable reply.
I apologize for the gross error in calculating the arrow, I considered the square of the diameter and not the radius
For an F11 the arrow would be 1.42mm instead for a 3.13mm F5
I don't know if this experiment is worth trying and at this point try to consider a larger diameter as you suggested. However, the question arises spontaneously, bigger than it? For large diameters, what could be the problems of processing for a neophyte like me?
To glue the plates together, it might be valid this product?Anyway, two 19mm blanks of calcium sodium glass to make a 300mm F5 I bought it from a glassmaker a few months ago and I will start processing as soon as possible.
With a good chance, on that occasion I will certainly refer to a lot of interesting information on this site and draw on the experience of the veterans who populate it by asking questions, I hope not too trivial.Thanks again for the useful comparison.
Today I took some photos of the small plates that I link below:
I was thinking of cutting them with this tool:
and to help me in the circular cut with this suction cup:
From BricoIo I found this silicone it transpires that, with the exception of its NON-liquid self-leveling consistency, it seems similar to the one that maestro Lolli advised me.
Referring to this very interesting article to have an arrow that is below 6mm, with a 250mm diameter mirror I should consider, if I'm not mistaken, a focal length of 2750mm. With this estimate I would have a 5.68mm arrow, getting close enough to 6mm and therefore the first question that arises is related to the resistance to deformation and thermal expansion of the hollowed slab glued to the one below.
Then there remains the perplexity for the focal ratio which in this case would be F / 11. Ultimately I would have a probably poorly performing mirror, with an unwieldy focal length and a focal ratio not necessarily desirable.Assuming these considerations of mine are correct, the idea of coupling the slabs (for example 3) doesn't seem to produce a good solution. It would probably have the sole purpose “didactic” to start gaining experience, which I wouldn't mind but ultimately wouldn't allow me to have a usable tool.
I await suggestions and considerations in this regard.
