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hello Giulio,
1) – carborundum, dopo aver letto ho optato per questa sequenza 80-120-180-320-500-800 with 80 a scavare quasi tutta la freccia
2) – pianale tondo per il fusto dell’olio (devo trovare qualcuno che faccia tagli tondi da 580mm oppure faccio un quadrato e lo adatto
3) – pece ed ossidi per lucidare.
Purtroppo non ho modo di avere accesso ad un test di focault o di Ronchi, questo mi frena ma se trovo qualcosa in rete (in Italian) provo a costruire io qualcosa.
4)- Parto con passate cordali per scavare la freccia, poi una volta a misura? Specchio sotto e c.o.c. con le grane più fini fino all’eliminazione dei crateri?Ti rispondo coi numeri:
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R1): Tieni conto che con la troppa precauzione farai sicuramente una focale più lunga del desiderato, perchè con le 1/3D c.o.c. non scaverai più, o scaverai veramente pochissimo nell’uniformare la sfera, portandola fino al bordo…Ma la freccia rimarrà quasi sicuramente quella raggiunta dalle passate cordali.
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R2): In un brico center ti fai tagliare due pezzi quadri di compensato spesso 15mm, uno dei quali tre centimetri più largo del diametro esterno del fusto, e l’altro del suo diametro interno. Poi tiri le diagonali e con un chiodo, un cordino e una matita, disegni due cerchi tangenti i lati dei quadrati.Basta quindi un seghetto alternativo per tagliare seguendo il segno della matita.
Una volta tagliati i due dischi, prendi una raspa e rendi passante il disco piccolo. poi li sovrapponi e li unisci con tre viti. E il coperchio/piano di lavoro è fatto.Il mio fusto era ovalizzato e con la raspa l’ho adattato facendo poi una freccia sul fusto e sul bordo del coperchio per trovare il punto in cui …..con un pugno entra e sta al suo posto senza gioco.
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3): pece e ossidi da lucidare sono ancora lontani, ed hai tempo a procurarteli.
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4): Esattamente: Passate 1/3D c.o.c, dapprima con la grana 120 fino a scomparsa dei crateri della 80, poi con la 180 fino a scomparsa di quelli della 120… e così di seguito fino alla 800.Ti scrivi su un cartello le 4 regole delle corse 1/3D c.o.c, that are:
1 – Con specchio sopra scavi (di molto poco) the center:
2 – con specchio sotto svasi (di molto poco) il bordo;
3 – Alternando le posizioni mantieni la freccia invariata.
4 – Con le corse 1/3D c.o.c in avanti e indietro, e 1/6D o meglio 1/8D (…ma dovresti “pensare” il debordo laterale uguale a zero) ritorni (molto lentamente) verso la sferaSe fai troppe corse troppo “lunghe” (<1/3D) e/o troppo “larghe” (<1/6D), non ottieni la sfera ma neanche la parabole è sconfini nell’ellisse o nella iperbole.. e fai “game over” dovendo poi tornare alla sfera (senza danno se non del lavoro e tempo in più).
Then: Ogni tanto durante il lavoro misuri la freccia, e se si muove inverti la posizione specchio-utensile, e fai qualche seccata di recupero
Read the article at the following link with the list and the quantities that I used for my 250 (with the exception of grain 80), which do you think will serve less than 1kg:
and on the particle size of the abrasive, from one to another see:
https://www.grattavetro.it/abrasivi-per-il-grattavetro/.Abrasives I purchase them on the web in bags of 1kg “mounted LAPIDARY” in whose site type into the query box “silicon carbide” and go.
If a video is missing a grain, ask the availability by phone or email, because usually they have it.
Similarly you can do when you try ceria (it takes less than 250grammi).
thoughts:
1) Unfortunately know the necessary amount of silicon carbide can not be utility, because they are sold in bags of 1 kg, which it is a quantity gradually increased use which do, especially with the fine grains (see the quantities used for my 250 article referred to above).2) My series of abrasives is designed to halve the diameter of the grain from the previous to the next, so as to optimize the work and also be able to see agevomente with a lens, and then with a microscope, the disappearance of the previous craters. (If the grits are little different from each other, also appreciate the disappearance of precedents that indicates the changing of the grain, it becomes difficult).
3) Choose a finer grain makes you work harder, but from a practical point of view is equally well;
4) choose a less fine makes you work less but then you'll work more with that of the next step.I have hex nuts M8 13 and are fine.
I think that 30 is a good thickness. The difficulty will be to find a package so small for the amount of gypsum . Taking the bill with the specific gravity 2,6 (if it is right) I would 2,5 kg of your needs.
I, too, in the laundry I have a drum former mineral oil. As ballast I put 75 bricks (about 75kg), and I need to keep in a safe inside “the material “….which makes mess”
my other half of the sky.But look what a beautiful movie of Stephen found! I did not know the existence.
Stephen is one of our Forum, and is a good grattavetro….and also the fact that beautiful tool plaster with buried stoneware pistrelline!
And bravo Stefano!And, the chordal is passed.
The number of forward ran back; as well as the small step around the table and the slight rotation of the mirror in hand, They are free cadence. In the sense that you do random as you want.For example, I find it best to me not to count, and distract doing a continuous work, ie small passetti around continuously around the table, and continuously altreattanto to each rotate it back and forth a little the mirror in hand. You are free to choose what you like it. The important thing is to keep the random symmetric and avoid any repetition.
Plaster: I used the “GC FUJIROCK EP plaster stumps for class 4” This brought to pack label 5kg.
It was yellow coloree (5kg 35,90 euro 4 years ago), l-I cast on a 300F6 to refigure, and I was fine because I have not thought about the overheating and the mirror in normal glass 30mm has not broken (You perhaps know that it was a type of those who do not so much surricadano)?Even with the mirror still plan to dig should be fine chalk, because the tool only works in compression against the table, and with past cortade always keeps the mirror in his hand.
So the effort you do premendogli the mirror against, the tool being well supported with its back on the table, definitely does not break.
Fear is always, and I remember that I end I made the tool often 5cm, that on a diameter 300 They were even exaggerated.The bolts or stoneware piastrelline are the part of the tool wear, because the glass would immediately abraded from carborundum.
Then an armed tool steel nuts or stoneware has the desired resistance, although contour of those armor inserts there can chalk 2 Mohs.As for the resistance of the anchorage of the inserts on the tool surface, the inserts in steel nuts have a thickness greater than that of stoneware piastrelline, and a threaded hole that gypsum filling makes it impossible for the disconnect that could happen to stoneware piastrelline glued epoxi…(I do not know than those flows directly into the gypsum.
The tool with steel nuts would be particularly more lasting.
A tip is not to stop at 95% the excavation of the arrow, but to go up to 99%. That precaution too “lenght”….spessissimamente does get newbies a mirror longer than desired focal, albeit slightly).
No need to apologize to the questions you ask. And much better them!.
The French text has many drawings and sketches very well made and with captions “they show” the limits of various races.
You have correctly described how it executes the 1 / 3D c.o.c But this is not used for the excavation of the arrow, but only at all stages that follow its achievement until at least 98-99%, taking care not to protrude laterally. (Steps are: Unification of the tool bends and mirror to form the initial sphere; Puddling of the surface with grit away finer way; Polishing with pitch).
To dig the arrow until it 99%, Instead it uses the past with some chordal spent “8” (or to infinity), With the chordal the mirror is held in the hand with what will be the reflective surface facing down, and rubs its center, against the tool, along its circumference of the imaginary ropes, putting a lot of pressure with your hands.
Ok for bevels.
As you will see in the movie under the following link, in the machining tool it is used in a dental plaster with drowned of hexagonal steel nuts of dimesioni about M12 (hex 19).
In manual processing would not see contraindications, because of the arrow in the excavation it takes place the mirror in his hand and is strongly rubs against the tool which is supported flat on its entire rear surface in contact with the work table. Then, the tool plaster is stressed only in compression, as it can give its maximum resistance.
I have developed a tool for dental gypsum “naked” (without bolts), just to refigure (then with the sole use of the pitch) a mirror from 300 mm, and I do not live in esperiuenza roughing hand.
For the realization of a tool with metal nuts, you can view the following minute from Gordon Waite 6,32 on: “Making a steel grinding trool”.
Commenting on the movie I can say that the raw mirror that Gordon has worked for a 500F3,3 and was provided with the curvature of the arrow designed to soften the blank of the oven, lying above a shape that metal guess, machined with the desired spherical curvature.
Therefore, the curved surface thus is no longer to be excavated but only to unify the radius of the sphere in the local radius diversity due to the thermal process.
Instead, to achieve the tool with metal nuts copying the curvature of the blank, it is interesting to note that Gordon puts on the mirror of a transparent self-adhesive plastic sheet with the adhesive facing upwards helping to keep metal nuts arranged in a quasi-random manner. The rest is also intuitive to those who do not know English.
The only attention to be reckoned with, It is that the dental plaster has a high mechanical resistance, but in the casting starts a heating resistance proportional to that which is strongly exothermic, (perhaps even 70 ° c …because there will withstand contact with his bare hands).
Heating that lasts all 40 minutes to complete curing of the plaster. And that concentrated heat and quite sudden costituise a great danger of breaking, for one of normal glass mirror calciosodico (ie not pyrex or other type of borosilicate, by its very nature thermal shock resistant).Link to video:
…I forgot to remember
that before you start to scratch you have to make a chamfer of about 3 mm or more , on the 4 edge of glass panesMaybe you're lucky Andrea because the text is in French Texereau.
And, the past 1/3 c.o.c remains the same from the end of the roughing made with that type of chordal, until the end of polishing done with pitch.
For past 1 / 3D c.o.c (center over center, ie the center of the center) It means a movement to and fro diameter of the glass in your hand, always centered on the glass that is on the bench, and such that in your back and forth, overflows in total 1/3 the diameter.
For example: For the mirror diameter 200mm is the total ooze (200*1/3)= 66mm, ie 33mm pushing the center of the glass in your hand 33mm over the center of the glass that is on the bench, and idem pulling inietro, suparerai towards you the center of the glass on the bench 33mm, with a total stroke of 66mm which is.In general, you should be vigilant with past 1 / 3D c.o.c, not spill over in the left-right direction, more than one or two centimeters, (therefore working manually must think of a lateral swiveling out zero, however, because a little is always equally overflows).
SE is exaggerated in sideways overflowing, you do not get more a spheroid, but even it exceeds the parabolic shape, and then you have to do a lot of work to get back to that sphere which could already be produced before, minding to contain the lateral swiveling out.Of course in those movements going back for all kinds of past, cammninando must always move around the table in small steps in a sense, and simultaneously with each round of the glass back which holds, it must rotate a fraction of a turn in the opposite direction.
Which, with round table and high, It is a continuous and automatic movement of the body that personally prefer compared to what Occor done using a table that does not allow to walk around.With a work table, or a bench to John Dobson, which does not allow to walk around, We need a little complicated life counting a number of comings and goings, and then remember to turn the glass that is on the bench of an angle equivalent to that which would have been a step around the table, and turn the glass that holds to the contrary….and less pose a glass muoverne another, and unless there is a risk of a rupture accident.
The risks of the pose and take the glass out to so many times, There are, because to achieve a 200F6 on average it will take approximately one hundred thousand forward ran back that last a second, (I've got used 77 thousand to realize my 250F5, I bought already blank to the final arrow).
In all then, those one hundred thousand passed back and forth from a second term, they only 28 hours of total work exerciser. But put down a glass to turn each other once (for example) every 10 He ran forward back, It would mean making ten thousand movements “puts – tour – take” that you do not but if you walk around the table.
As regards instead the past W, they do not maintain the perpendicularity of the centers of the two glasses, but describe a displacement of one of them in the right-left direction or vice versa, to draw a hypothetical W, and therefore it is used almost only in parabolizzazione.
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Among our products there are two on the last chord / excavation of the arrow:and one on the last 1 / 3D c.o.c:
oooooh EVVIVA!
I see you going to get yourself a 200F6.5 which is ideal to begin.And if you have "extra-watched" French movie of the 200F6 https://www.grattavetro.it/tutorial-video-costruzione-di-uno-specchio-parabolico-200f6/ (which I think is much more likely than the overly simplistic John Dobson)…
And also if you're a person who wants to invent its experimental, but he prefers to achieve the goal with the greatest possible safety, thus following the path “canon” whose secular way has already traveled knowing the stages…
And finally if you are holding the text of Texereau downloaded here: http://www.astrosurf.com/texereau/chapitre.htm
..at least in 4 chapters defined as such only by the splitting of PDF documents in which the book has been split free download, and are): ….introduction; chapter 1; chapter 2 , chapter 2 bis comprising all chapters of the book until the parabolizzazione…Then you're in starting work conditions having well over 90% of possibilities to take gloriously term. Since surplus here in Grattavetro there is parallel to your work, Also our help.
Coming to your questions, ask where:
1) "It is advantageous to have two equal disks for processing"?Is’ advantageous, because, for example, John Dobson in his movie, He realizes a mirror "about" 400F6 working it with a sub-diameter tool: Utensil which by its nature does not "scratch" uniformly across the surface, and then it produces a beginner confident zonal errors affecting the quality of the mirror. Errors that can not physically intervene if you use two of the same diameter discs.
2) "With regard to the work station it is just necessary to rotate around or just only rotate the mirror / tool as it does Dobson"?
Just also only rotate the mirror and the tool, and it is a matter of taste, Floor Cleaning and anti-nuisance cervical posture: In my case, I use a drum former mineral oil with wooden lid, that it allows me to work from standing, with a natural upright posture that does not teases the cervical spine, and with a large enough work plane to allow an excellent cleaning. The book has Texereau images on page 28 on the various types of work table).
3) "Where can I find a good tutorial on the type of pass to do? I mean a kind of manual without hopping in various posts "?
A tutorial on the type of pass to do (I know) does not exist, if not looking at the various stages of processing in the French movie. But you can find all the information on the book of Texereau, because the past to work with full tool diameter are only 4 in all the work including parabolizzazione, and generally have complementary affection depending on whether the run with mirror below or with tool under.
They are:
DIGGING FOR ALL THE ARROW grained 80: Passed chordal with some variant 8 or to infinity. (chapter 16 page 30 del Texereau, con fig 18 A e B, page 31
(to make a 200F6,5 need to reach an arrow depth 1,92mm; and the parabolizzare 0,7 microns; while
to make a 200F6 would reach an arrow depth of 2,08mm and parabolizzare 0,9 microns)FOR THE UNIFICATION OF FIRST BALL: Passed 1 / 3D c.o.c (that is 1/3 diameter center of the center).
FOR REFINING THE SURFACE WITH UP TO THE GRITS 800: Passed as above 1 / 3D c.o.c.
POLISHING WITH THE PITCH AND CERIUM OXIDE: Passed as above 1 / 3D c.o.c.
FOR PARABOLIZZAZIONE: Corrections with past 1 / 4D c.o.c. Or passed to W with a width W of the variable to dig more or less in the areas to be corrected, or 1 / 3D back towards the ball.
4) "As far as the focal thought to do so 1300mm f6.5. Of course I have no way to make rhonchi, Foucault or similar ".
After the polishing, if you have not made a perfect sphere, but as often it happens, you will have an already spheroid slightly flared towards the patabola, you can put the mirror as it is, not aluminized, in the structure of the recipient telescope, to see how it presents the view of gradually bright objects, like the Moon or Jupiter, or more challenging Saturn with eye from about 9mm)…
So surely you'll see your vision you suggested / force you to build yourself a simple Foucault tester, like mine which is exactly identical to that emblem on page 59 del Texereau (chapter 30 the book but well understood in chapter 2 bis portion of the pdf downloadable), to verify progressively with the Ronchi grating, or Foucault, what fixes to apply to get the best quality you will want, before sending all'alluminatura a mirror definitely higher than commercial grade.
In that case I think it goes to taste.
For example, I would not like zero CPL, just because maybe it could make me appreciable the decrease in brightness at the edge compared to the center of wide-field eyepieces from 82 ° up.Furthermore, I would think that the difference in definition between the two obstructions is not so appreciable. So I'd stay on the second case.
Hi Andrea.
Sull'Upload (and use Atmos) Take me off guard.We ask the help of Massimo.
But I think Atmos is much better than my method “St. Thomas” based on the CAD drawing.
With a secondary 28mm diameter ports CPL 6mm, out of the optical tube at a distance from it of 63,5mm, which will be the one that should be filled by the thickness of focuser more camera.
But in that case you must also check how to use eyepieces that are more easily “short” the set of extracted focus for the camera, and it could be forced to use the extensions, or vice versa normally use the eyepieces, extract but with a greater fire barlowil required by camera.
If the measure, which goes from the base of your focuser fixed on the optical tube until the sign of the position of the sensor of the camera, It was greater than those 63.5mm, You will need to further lower the secondary to extract greater fire. But you'll need a secondary mirror a little bigger.
If you want to be very sure you get yourself a paper drawing in which check your measurements.
In practice regarding the verification you can use all your eye, you should prepare a multiplication table using another any telescope, and focusing with each of them, with and without barlow lens, an object, measured with a caliper, and recording always for each of them, with and without barlow lens, the measure that elapses between the abutment of its barrel, and a common reference, convenient and fixed taken on the used telescope.
With this table would discover what the eyepiece of your park, which requires the greater introduction into the focuser.
AND THAT will be the most critical eye for which you will need to adapt the focal extraction of the new telescope. …(Given that all the others will be in focus in the extraction, that is gradually moving away from the telescope).
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