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Ciao,
so as not to miss anything I have a small hill in the center ,my usual adaptation error due ,I think in some work session that I have a little neglected…. ok it doesn't matter it starts again! I was thinking to remove this hill to work at W with the width of the stroke a 3/4 the diameter (so I read) what do you think ? There are other methods? Some advice……I rebuilt the tester from scratch.
http://s15.postimg.cc/4wtzkgkh7/IMG_20151219_075939.jpg
http://s3.postimg.cc/b54475ho3/IMG_20151219_082037.jpg
http://s18.postimg.cc/oz623fpbt/IMG_20151219_082115.jpg
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http://s28.postimg.cc/lgxu4wy7x/IMG_20151219_082331.jpgBravo Maurizio, it's much better ! you managed to improve the fit. The area with little contact has shrunk, Now a small central area is missing that still works with poor grip. If you can fix this too you will see that the knoll goes away in a few sessions. I would not change technique until you have a completely well adapted patina, also because the result would not be as expected…
Ciao,
what do you think of these? I can start parabolic?http://s4.postimg.cc/72796v2ul/IMG_20151220_105641.jpg
http://s16.postimg.cc/cm2n3kolx/IMG_20151220_111003.jpg
http://s18.postimg.cc/6c6rsls61/IMG_20151220_111253.jpg
http://s9.postimg.cc/nn70zsbnz/IMG_20151220_111442.jpgCabbages Maurizio really well done !!!
I am struggling hard to get this blessed sphere, between adaptations, pitch too hard, wrong channels and so on and so forth. ..
How you then worked to remove the mound in the center, switch to W or classic 1/3 COC ?hello Henry,
sincerely with 1/3 COC I didn't take big steps forward then looking on the net and re-reading the tutorials that are and experimenting a bit of everything I found this site
that helped me http://www.nicholoptical.co.uk/ATM.htm and take a look at how to interpret the ronchi.
However, I made passes to remove the hill > 1/2 COC almost half diameter and then I was making a central hole; then I have passed 1/4 COC and in a few sessions and checking each 2 min approx ,because’ even if it doesn't look like cerium oxide, it works quickly. But all this done by hand with a machine, I don't know how to do it.maurizio
Maurizio eye, that reading on the web is written about everything and the opposite of everything… this is not to say that the site you refer to is not reliable, but only that the best teachings are those that derive directly from one's own experience.
So I invite you to reflect by analyzing what you have done:
– you have lengthened the race to 1/2 ( I assume with pressure in the center and then find yourself with the central depression)
– you have reduced the ride to 1/4
if you did the “media” and you worked directly with 1/3 you would have had the same result.
what corrected your form was not the change of technique ( which basically remains a central race and little changes ) but only the achievement of optimal adaptation.
What is hard to accept in this “craft” is that the techniques alone are useless if all the rest of the setup is not optimal. Sometimes I have read about some who have invented the most “picturesque” geometric shapes for the passes, without worrying about adaptation, of temperature variations, the hardness of the patina, incorrect position of the hands, etc… with the result of not being able to understand why the “techniques” they didn't work.However, I congratulate you because the sphere reached is excellent, and you can certainly proceed with the parabolization, however, I urge you not to “archive” what you have done so far without in-depth reflection.
Having generated the sphere with the complete understanding of what led you to the result, it will be fundamental for any problems you will encounter during the parabolization phase, so don't miss this opportunity to build your own “database” enriched by the in-depth analysis of the path that led you to achieve this important result.
Anyhow , you are doing a good job, bravo !
To reach the sphere, I went through problems that I gradually managed to solve (pitch adaptation,raised edge, hill in the center and hole in the center,tester rebuilt with Giulio's advice),in short, I had a good experience and in any case I have thought about every problem a lot and now I have understood at least up to this point everything I am’ success and why me e’ success and how it is’ been fixed. Thank you all.
Now the parabolization chapter begins and I am re-reading all the topics on the site concerning this phase. I already have some questions but when I tackle the topic in practice, I will ask them, always hoping for your help.maurizio
Hi guys,
I have some questions for you:
1 I have to use the same layer of pitch to parabolize (no star shapes or similar)?
2 I was looking at the pictures of the RonWin20 program and I don't understand when a parabola is undercorrected or overcorrected the difference and’ so minimal,they all look the same,this is because I wanted to continue in this way: first check the dish with the ronchi and then once you have verified that e’ correct go to work with the focault what do you think?hello Maurizio.
To parabolize, the full diameter tool is used which created the sphere with the same patina of pitch. only the strokes to apply change and become W-shaped, wider where it is necessary to dig less and denser vice versa.Star tools are generally intended for large diameters, to machine work, or with sub diameter tools.
In parabolization, the tool should possibly be dragged from the edge without placing your hands on it because the material to be removed is of the order of a few microns at the beginning, which become a few nanometers (that is a thousand times less) towards the end.
Furthermore, the support of the hands results in an increase in abrasion, and therefore the addition of an unpredictable disturbance variable because it is difficult to quantify and imagine, which disturbs the predictions of the neophyte, who, on the other hand, must stay on the ball to understand what is wrong in order to program the appropriate corrections.Parabolization corrections up to a focal ratio of F5 are feasible with the full diameter tool, and generally they are performed by implementing contained overpressures at the passage of the’ tool on the salient circular ring, which therefore results to be lowered.
hello Maurizio…congratulations for the excellent sphere…
Verifying the shape of the mirror with the Ronchi alone is practically impossible, or rather with Ronchi you can check the general progress of the works and the presence or absence of gross or zonal errors. While as regards the quantitative evaluation of the surface, Foucault must necessarily be used…So basically in the parabolic phase both tests are used in tandem as the information deriving from one completes that of the other.
Right from the start, I would invite you to use both tests, even if initially when the sphere is still slightly flared, the readings with Foucault are more difficult, but this allows you to become familiar and practice with the test in view of the final phase during which the sensitivity acquired in reading the draft of the various areas becomes fundamental. The Foucault test is necessary to know the degree of deformation of the surface that we have generated with the perfect polishing, which must be well finished, to avoid the risk of encountering a lucky good dish when the necessary degree of gloss has not yet been obtained.
In other words, the first cognitive Foucault test of the shape of our pseudo sphere is performed, when you decide it's time to start parabolizing the mirror.
For setup and testing there are articles to read in this blog; but the initial technique is described in the article report of the parabolization of the mirror 250F5.
Summarizing the topic:
The first test is done “indicative” with Foucault, without using the Couder mask, , measuring the draft in the center of the mirror and then measuring it at the edge, and subtracting from the value of the edge draft that of the center.1) If you have a perfect sphere the result of the subtraction will be Zero deformation (the sphere has a single radius of curvature).
2) Instead if you get some value, you will need to compare it with the value “center minus edge” which has the reference parable, which is the one obtained with the calculation (hm ^ 2 / R of the edge minus hm ^ 2 / R of the center).
Meaning of that found value:
For example, if the reference parabola has a difference of, let's put 6mm, and your measurement gives you zero, then you have a perfect sphere.If instead the difference gives you a value between zero and 6mm, then you are already in the presence of a parable that has begun.
If the difference gives you a value higher than 6mm, then you have already passed the parabolic shape towards hyperbola (runs too long and / or too far right left). A hyperbola is impossible to correct in a parable (because you can only remove some glass from the mirror and in this case it would be necessary to add some because too much has already been removed). Then you have to go back to the sphere by working with the strokes again 1/3 c.o.c. to clear the error and go back to try again.
Hi guys,
this time no questions but only to wish HAPPY HOLIDAYS to all the Grattavetro editorial staff and to all those who like us enjoy capturing the stars.ps:I haven't captured any yet but I'm trying..
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