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As for the tensions within the blank, the article that Giulio posted to you is very valid ...
These are the tests I had done on my blank once I got out of the oven:
To obtain images of internal tensions, I put the blank in front of the completely white screen of the home TV (ok TV, PC screen, etc ... but not the screen of old cathode ray tube TVs)
The completely white screen was obtained by sending a video of a couple of minutes found on youtube.
After that, just look through the glasses for 3D movies, they also give you to the cinema, to see the states of tension in the glass. You have to figure out which is the right way to put your glasses though.
I'll explain.
if you look at the first image you will immediately notice that the screen is in the background (that of TV) it is white and can only be seen on 4 position the internal tensions at 90 ° from each other, but this is not the correct position to place the glasses.
If you start rotating your glasses, you will always see the white screen and those 4 colored areas turn with them, until you get to a point, where the TV screen suddenly changes from white to black, as in the image below.
Here is the correct position to observe the tensions.
In the specific case, as you can see there is a kind of dark cross in the center, which I think is due to some phenomenon that does not depend on the blank because it remains identical, in the same position, even if I rotate the blank.
What is of interest instead, it is that blue-blue circular area that extends up to 3/4 the diameter (constant voltages or not present in this area) which then, it fades first through white until it turns yellow. This shows me, than that chromatic variation, is due to internal tensions, but to be honest, I would not know how to evaluate its size. It may well be that the tensions are small and within a far more than acceptable limit.
To get the pictures you saw, I had to place the glasses upside down, that is, with the arms facing forward, because if I put them "straight", that is, with the temples facing the observer I always saw an image of this type:
and I could never find the position for which the screen behind it was black.See you soon and good work…ciaooo
Hello Marco,
I just read that you've also done finite element simulations, of the structure of the blank that you would like to obtain…You would show some results?
Or the results of the various configurations you have tested (if you have tried more than one)?
thank you, it would be very interesting… Hi everyone…
And, I would definitely recommend the 3D printer, I think it is the best purchase I have made in recent years…For charity, you have to know how to set it up well, know how to use CAD programs for 3D modeling and have a minimum of engineering criticism in order to create light but at the same time resistant components, but for the rest it is very useful ... I print everything.. To give an idea of prices, suffice it to say that per piece whose printing time was approximately 5-6 hour, the quote made to me online by a firm was around 300-350 Euro, while I paid for my printer in total 205 euro. It arrived in kit form and I had to assemble it entirely, however it was not a problem and today I am fully satisfied with it…
Hi everyone,
I saw only now this thread…
no Marco, amateur is absolutely impossible to build a telescope mirrors that multiple functions (specific functions that, because it does not work you can very well…ah ah ah..
).
The machining tolerances, both of radius of curvature, both conical constant are too thrusts for an amateur builder, not to mention the tight tolerances of positioning of the mirrors, to ensure that are able to work in unison.
If you can affect I suggest this article, in which they are shown different machining tolerances for the GMT (Giant Magellan Telescope, 24 meters in diameter!!!):
http://www.gmto.org/Resources/GMT_5494-8.pdfMaximum: sooooo nice that document on’ E-ELT, I had not yet read.
However, both the E-ELT primary is formed by a whole series of hexagons every one worked so as to form at the end of a single ellipsoid with K =-0.996. So I'm quite contoured, every one, with its own specific form of dressed ellipsoid, are no plans. Then there are other 4 mirrors, of which a secondary and a tertiary conical, to eliminate most of the optical aberrations, a quarter mirror plane on which intervenes adaptive optics and a fifth that sends toward the fire Nasmyth the optical beam.
Another impressive thing is that the primary has an F # = 0.93, which results in a primary arrow over 2.5 meters!!!!!!!!!!!!! Not to mention the size, of rocks in play, of the wind relative forces produced by such a large dome, and the fact that it will be built in a very seismic zone…
No, the arrow is of 5.075mm…
In formula (approximated) to use is:
r^2/(4*focal) oppure r ^ 2 /(2*Radius of curvature)
where bending radius = 2 * FocalAnd, this can be a proper way to do, in fact both the gypsum cylinders in the mold, both perforated disks in the second example that I have given you, are all positioned exactly in 18 Suggested support points by Gui plop. Then I draw the ribs starting from these fixed points.
Nobody, however, prohibits to do differently and use a diagram hexagons, square, triangles, then will you have to figure out where to best position the support points…
In short, the viable ways are many, It is up to you to choose the one you deem right and even easier to do (which it is not a thing to be underestimated)… in well, there is no doubt, to speak with someone who handles and fuses glass all day can only be of great help.
Although they are not the astronomical mirrors their industry experience will definitely be able to provide valuable information… Ah, ok, I understand what you mean…
eh, There may be many ways to do this, as you see in the picture above, the plaster mold has a whole series of rectilinear cavity inside which will form the ribs, which then converge in “knots”, where there are those cylinders purposes and long chalk. In this way I got a blank with a similar back to this:
into those cylindrical holes I would then went to innestarmi with some kind of pin outgoing from the primary cell.Or as I did here:
in which I predicted in the back, a whole series of perforated disks, in which the hole had pasted into threaded plastic inserts, on which I then went to anchor with screws that I predicted the triangles of the primary cellbut I assume there are thousands of ways yet, you can really indulge your imagination…
Then, I state that I did not understand what you mean by: “create the reverse side in order to have the supports to the support”, but vabbhè…
As for fusing, I first realized the plaster mold, and then I loaded with glass grit, with which the temperature has merged.
But here I should open a whole chapter on the difficulties that I encountered, from the non-perfect fusion of the flakes due to the temperature not adequately high, to the temperature holding time that is a whole say, the air bubbles that are trapped in the molten, to the mold resistance, to cracks that are generated in cooling etc.…
Precisely because of these and other problems, that still would not be able to avoid with certainty, I was at the end directed towards the softening process rather than in that of pure fusion.Here are a few pictures of the first race I had done (a lot of hours of work, for a negative result. But the game is so and we must accept…
):P.S: but I live in the province of Vicenza, and I also I graduated in mechanical engineering, But in Padua…
Hello Marco, a welcome from my…
mechanical engineering, good, where ?
Then the construction of a glass blank for fusing is not simple, and I'll tell you why I did a lot’ evidence, go all more or less OK, once for one reason after another…Anyway, this allowed me to experience and understand that, obviously, as in all things, serve the right equipment and machinery, otherwise the result will not get there…
Having said that I am very curious to read and understand how you intend to implement your project, that if you want, I can somehow, try to give you some tips for what little experience I gained.in the meantime if you want qua laws:
although I have not given everything I've experienced, there's a little something… Hi Nicola, A warm welcome also from me…
Un 250mm mi sembra un’ottima scelta come prima lavorazione, con un buon compromesso tra “facilità” di realizzazione e soddisfazione poi nell’osservazione…
See you soon…ciaoHi Stefano, a very warm welcome from me, here in the forum…
I didn't own a telescope when I started scratching either, and even today the only one I have, that's what I built myself, and I think that was a big incentive for me, since if I intended to observe something, I had to finish the job…
Anyway returning to us, I tell you that both of the types you mentioned, the 300f / 5 or the 200f5-6 are feasible as a first experience. Clearly with the 200 easier and faster to build than the 300, something that you could use to your advantage to learn how to manage the various processing stages, and then try your hand at already a wealth of knowledge, in the realization of a more demanding project.
But, as I told you also the 300 f / 5 you can do it very well, also because from the presentation you made, I understand that you are not one who gives up that easily… Then you also have to see what you would prefer to observe, se planetario o deep sky, and the quality of the place from where you would usually observe…
And, also I have “tinkered” deal with the special software POLSIM, more than anything else to begin to realize the dynamics at play, and the effects of various settings on the processing. But even as you say then, real mastery and proper management of the machine, the only acquire with the actual use of the same…
