Building a Cassegrain

[Lelio]

I would not be unwelcome, but with the grain 40 enough 8 Hand hours without rotating plate to dig 6 mm, and then subsequently 1 Now for grain in the best hypothesis and a pair in the worst. Working in manual must be smart, or you'll kill fatigue.
One trick is to make a plywood diameter mirror disk if you work on it full diameter with a border to contain it, practically a lid to which are added two handles to be able to challenge. On top of this “tool” leans a nice weight to the gym at least 5 kg…… or a car battery, back and forth without pressing, and with a good grip. Too bad I do not have the tool would otherwise put the photos that are more explanatory.

[Lelio]

Gemini Excuse me if I was a bit brutal, but I just had a discussion with my partner and you do not have any guilt, but I have heard criticisms and proposals similar to yours, plans for the future mirror with absolutely legitimate reasons but I am a visualist and I do not care the scientific aspect but enjoy nature, the moment, the moment, how to observe the sky is a personal matter. For me it is rapidity of assembly, be up and running quickly and not waste time in set up the telescope complex to fully observe the sky in the few perfect moments, dob forever.
No photo, to those who have to show photos when you just bring your eye? Those looking for asteroids, comets or extrasolar planets are a very small group of people who make a second absolutely boring work, hours of pictures and monitoring the work done with painstaking precision. To me there, Instead there to see something nice to my children and grandchildren, convey the wonder of enjoying nature in general and specifically of the sky. The wonder that for thousands of years has led generations of astronomers to observe the sky.

[Massimo Marconi]

haha Lelio It seems a bit’ “Taliban”, a fundamentalist of the visual ! It is fine, for charity, I have visualist , however I believe that photography is an important scientific research tool, and is not, absolutely not “boring” and that the small group of people is due to the fact that for photographing takes a lot more skill and preparation “simple” to observe.

However, everyone is free to think as he wishes, God forbid…

As for Geminimac ( Luca ), we warned some’ all the difficulties she had to face, but apparently this guy when he gets something in his head…

What is important is that one is aware of what that must be met so, a dedication to Luca with my best wishes:

[geminimac]

Kill as many negative opinions…if I had known before I never published my idea…I had only to follow the forum in silence as a good spectator least I would not have gone through a mad visionary🙃😐😑😔😕

@Lelio
As I have explained in previous dialogues with Julius Maximus and Mirko I want to be my experience that is not to impress strength and finish well ... "I would like to” and I say I'd like to finish what I started…I hope so because I'm not used to put people…if this is successful I will be definitely satisfied 200% but since I have a good chance of failing in the end I will have lost only a little’ time for a hobby began recently and 200 euro spent on the purchase of raw materials(glass and abrasive)…you know that the time for grattavetro is not a problem ... the important thing for me is get to the end, finish what you started!

As for the five-mirror system it is not safe to 100% who fail to complete, Massimo probably like I had mentioned earlier in the end we'll have to remove someone for optical management problems ... I'll see him after! For now my only problem is to finish the primary glass then pass to other ... considering I'm doing in his spare time ... I'm not killing fatigue, the rotary table I built precisely to avoid this ...

@Maximum

Thanks for your good wishes ... I need it!!

Mission Impossible!!

[Lelio]

OK Luca did not understand your approach. then good luck to your project even if they do not agree, this serves a school to confront different opinions.
I see the projects of any type only if feasible and above all economic and in terms of costs of intellectual and physical efforts.
But do not take my criticism as negative, it is not I raised doubts I have externalized you a little violently I admit.
Also I respond to Massimo Marconi, My location “Taliban” It is because I've seen too many young people who allow themselves to be fascinated by the beautiful results that can be obtained and then affacendati stallholders bustle around expensive recovery systems, but once you obtained those beautiful photographs and displayed like trophies to relatives, friends and lose interest in the message boards, some after a few months, and telescopes take the dust or are sold.
They spent a lot of money but they have not developed an interest in astronomy. For this reason I am and remain Dobsonian with a map in hand and I'm more interested to convey this sense of wonder rather than technical and scientific information, what comes next when it is supported by a real passion, it is love that drives people to face any challenge.
The most famous astronomers and known are prepared but also love their work, and this is not taught in school, but in the field and people like me go for dark meadows know what I mean.

[Massimo Marconi]

Lelio,what you say is unfortunately true… I think it's something that is not just about astronomy, but it is quite widespread among the younger generation in every field, the want everything immediately without the necessary preparatory studies and practical commitment to get results in a gradual manner , coming here also with knowledge and passion. Too often we think that “to be” that's enough “spend”.

[Lelio]

I guess that your last speech, Maximum, It is not reported to Luca, seems to me the classic white fly!
commits, risks, he studied and worked as a musso, forgive the expression dialect, and it is on its way to becoming a great grattavetro.
But maybe you have not correctly interpreted my post that, far from criticizing the younger generation was an admission of responsibility and guilt that instead we NOI old.
We, we were not able to pass on our knowledge, we do not have involved young people, we have allowed the manufacturers fuorviassero the meaning of’ amateur astronomy, and we have not done anything to get things back on track, which is not only sell.
This forum sheltering in part the things, at least tries! But we are too few in fact very few, so much so that some of our people “ri” all started from scratch because they have not found any that send information directly.
I think so because extremist? I do not think so.

[Massimo Marconi]

Of course it was not reported to Luca ! he is building with his hands the telescope and is engaging in something extremely difficult, whatever happens his work will be a person intellectually richer and more prepared, no one is buying an APO AND SUPER HD XD equipped with a dozen eye wide panoramic 16:9 theater effect and then sell everything after a year of inactivity, to buy some more exotic theme song.

For the rest, I agree with you, I was referring to a widespread attitude, surely a consequence of the causes that you say.

[geminimac]

After about three weeks we take stock of the situation…
After totaled 20 hours of work I am about 1,5 mm from the final arrow…I dropped the grain 40 to proceed with the 60….I thought about doing 5 tenths then move on to 80 and then the subsequent.
I tried to give the mirror a similar shape as possible to a sphere and as a first draft seems ok…obviously more accurately I will verify the shape just performed the first ronchi (I think the grain 150 It is sufficient for a possible reading of the just rhonchi?!?:unsure: )
Any advice is welcome!!

[Massimo Marconi]

Unfortunately not, to make the Ronchi Test is necessary that the surface is at least partially polished, otherwise there is no reflection. Even wetting the mirror you can not run the test.

[geminimac]

Well….It will mean that wait that the surface is quite smooth and then mention a first test ronchi…

Thank you!!

[Giulio TiberinI]

I do not know your method of working, but I can confirm that you'll find yourself with certainty to have a spherical fugura very well approximated (even without doing any proper test because it made it impossible for the impossible reflectance of the rough surface even when wet, but security is made possible precisely by this supplementary processing technique), if no roughing sub-diameter tools use, and hold the equivalent of straight races that sfeghino the mirror center against the tool edge, always turning in the hands of a round glass fraction that are moving, and at the same time turning step-by-step around the work table in the opposite direction to the manual rotation.
The same optimal result it can have bearing in mind all these devices to simulate them in your way of working indifferently by hand or machine.

At most, , the depth of the arrow in the center, you only have to change the type of abrasive and racing with those with the ooze 1/3 diameter (that is 1/6 forward and 1/6 and forth) to extend the abrasion of your ball to the edge of the mirror.

From that moment on, the aim of the work will only sharpen the surface with abrasive grit away finer way, maintaining stops the arrow knowing that with the mirror above the center approfondisci, while with the pecchio apptofondisci under the edge, and of course keep the unchanged alternating arrow.

[geminimac]

Unfortunately in my case I'm using just the sub-diameter tools…then I will surely have some surprises to be corrected… we will soon see

Ma 5 tenths with 60 suffice to fix the scratches of grit 40?!

Thanks Giulio

[Giulio TiberinI]

The average grain size 40 They are tabulated in 412 micron = 4,12 tenths, and for the 60 I'm 262 microns; the 80 and from 196 microns (2 tenths scarce). SEE TABLE scale granulometriva nall'interno Article https://www.grattavetro.it/abrasivi-per-il-grattavetro/

The size of a number of craters can also be greater than the grain size, but if you go down 5 tenths should eliminate almost all according to theoretical dimensiioni. will remain somewhat higher chipping here and there, and then it will agree to look through a lens, mark its position on the back of the mirror with a permanent marker, and then insist until you candellata, before switching to a more fine-grained, because the work of elimination only become more and more difficult and time.

[geminimac]

Perfect…good advice
The table you posted I will definitely comfortable…I have available a 10x lens that should be enough to identify the most profound signs

Thank you

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