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Stefano actually makes some beautiful pictures and, waiting for you to reveal yours “secrets”, I can tell you that, looking more at your images I think there is an exposure problem, as the background which is much less bright than the source, instead it appears correct as an exposure. This happens because the device used averages the brightness of the scene and calculates the relative exposure ma, in this way, consequently it overexposes a small area of greater brightness which is precisely what interests us. Therefore a first optimization consists in changing ( where possible ) the automatic exposure setting with the manual one by entering lower values, until the rest of the framed scene is fairly underexposed, quasi “darkened”.
Allora Finalmente sono riuscito a realizzare un’immagine decente però con l’inconveniente che adesso si vedono meglio i difetti e infatti guardando l’immagine A momenti mi prendeva un colpo. Ho le traveggole io oppure qui mi sa che abbiamo un piccolo problema? Le righe del Ronchi hanno un andamento diverso nella zona centrale rispetto alla restante parte dell’ottica… non voglio dire quella parola a livello scaramantico anche se credo che purtroppo vado a sbattere proprio lì; voi cosa ne pensate?
Allego anche un immagine della pece che ormai ha oltre 15 anni è fatta di pesce Cristallo mista trementina e a cera d’api non ricordo le percentuali ovviamente su una base di metallo
spessa 15 mm pesa un accidente ma è assolutamente stabile.
Great job Luigi, the image of the ronchi is ok !
Don't worry, there is no astigmatism, the center is spherical, then there is a small depression at half diameter and a decreasing peripheral area, but nothing that goes out of the ordinary, normal aspects and corrections to be made during polishing to get to the sphere.
overall the figure is good, perhaps there is a slight roughness in the peripheral part that should disappear with the end of the polishing, I continue to read you and I am very pleased to see that slowly the "family" is expanding, still not complete.
There is also a small difference in brightness between the left and right sectors which makes the opposite bands appear to be of different thickness. but this depends on the imperfect symmetry of the slit in front of the light source.
If the light source is a led, then part of the slit intercepts the brightest point of the LED, in practice the slit is not perfectly in the center of the led, but they are details, the substance does not change, it's a good job !
Sì ok In effetti la sorgente luminosa è un led. Proverò a centrarlo meglio appena avrò un po’ of time. Grazie tantissime dei consigli ma come dici di procedere… di proseguire con COC con utensile sopra? I didn't have much time to test the car this week? Un terzo del diametro avanti indietro…
I would continue with the central 1 / 3D runs up to the sphere, above or below in my opinion makes little difference. Rather, we should understand why the periphery has a tendentially different trend from the center which is instead spherical.
Almost always the cause is a suboptimal adaptation of the pitch patina, in which the center has a better contact than the periphery.
I would therefore also try to insert micro-grooves in the pitch squares, which certainly help both in the mirror-patina adaptation operations and in the effectiveness of the races.To be checked even if with the lowering of temperatures these days the patina is not too hard.
Good job Luigi! and beautiful image of the Ronchi
Also according to me it is to test the hardness of the pitch in consideration of the working environment temperature, which can create adjustment problems.
A very old pitch has potentially lost solvents in general, however, I believe only from the surface, So scratches help the compliance but also to put in place the underlying layers greatest potential.To see better and at a glance whether the adaptation has occurred over the entire surface of the pitch, Maybe you'd better do it by interposing a polyethylene sheet of kitchen.
Non-adapted areas will present the squares in part or in whole translucent, while those in contact will be full and bright color, with at most small and insignificant translucent areas not in contact, as you see in this image.
https://www.grattavetro.it/wp-content/gallery/c-pece/10-50F5-040.jpgAn adaptation that does not occur at room temperature can be helped making a bain-marie, (I once put on the tool of warm water rubber bag) but the forced temperature difference must not be elevated, because a pitch forcibly adapted and then not used in its optimal range of softening temperature (ie only maintained as such by the heat from the friction of the processing), It will create still the prevailing hardness problems, going to dig where she wants, and not following the bad habit of the wear surface, which it is what happens when there is the right balance.
So today a half’ COC polishing time 1/3 diameter with tool on top. I keep the pitch in contact with the mirror at home and therefore in a warm environment but the processing area is currently 11 degrees. I periodically check with a laser thermometer the temperature and the surface of the pitch and the mirror are regularly 20-21 gradi quindi penso che rimanga sempre ben amalgamata. Si sente anche che all’inizio sessione di lucidatura sono molto dure da scollare quindi c’è un contatto perfetto e la pece è perfettamente lucida sulla superficie ha aderenza su tutta la superficie dello specchio.
Ora però mi sembra che la zona centrale si stia abbassando un po’ troppo ho un’ accenno di bordo ribattuto che comunque c’era già prima (molto contenuto) non so se allungare leggermente la corsa delle passate, you who say?
Luigi, I believe that the problem is precisely adaptation: the half-diameter depression deepened further, while the center and the border have remained unchanged. Ronchi tells us that there is an area that is working more than the others and this with the past 1/3 D shouldn't happen.
Extending the strokes could help as the action of the tool would be extended, which now seems confined around the area a 1/2 D.
But the question in my opinion is another: if the 1 / 3D runs do not lead to the desired result, because the application of another technique should do it ?
I think it is better to find the cause that is determining this anomaly, the technique cannot be because as we know racing 1/3 D lead to the sphere, but only if all the rest of the setup is ok.The outside temperature of 11 degrees makes me think that, apart from the contact surface, the pitch is too hard to match the mirror, it is not able to deform to adapt to the evolution of the shape of the surface, moreover, in the transition from a warmer to a colder environment, there is certainly a variation in shape, perhaps imperceptible to the eye but very perceptible by cerium oxide.
therefore. La pece ha sicuramente lmitazioni dovute al fatto che è molto vecchia e che probabilmente è leggermente più dura di quello che normalmente viene consigliato. Per ovviare a ciò io la tengo sempre a contatto con lo specchio e in un ambiente molto caldo durante i periodi di pausa. C’è da dire che io uso un ritmo di lavoro piuttosto elevato (circa due passate al secondo) che quindi le parti in sfregamento tendono a surriscaldarsi e controllo ogni circa 10 minuti la temperatura della pece e e dello specchio che come ripeto viaggia tra le 19,5 ed the 20 gradi e mezzo; il resto dello specchio (la parte retrostante) è intorno ai 18 gradi e mezzo. L’ambiente di lavoro viene riscaldato poco più che altro perché il lavoro è molto pesante e suderei come un pazzo. Durante la lavorazione la pece fischia regolarmente, ed aggiungo un po’ per volta ossido di cerio con acqua. Si forma regolarmente la schiumetta e la scorrevolezza è abbastanza regolare. Il fischio è abbastanza sommesso e regolare e anche quello è segno che comunque lavora in modo ottimale. Appena terminato fino alla prossima settimana la pece viene portata in un ambiente riscaldato a contatto con lo specchio che essendo molto pesante la mantiene adattata perfettamente. Oggi pomeriggio ho proceduto a fare un’ora e mezzo di lavoro con specchio sotto ed utensile sopra movimenti decentrati col Centro in prossimità del bordo però compressione abbastanza intensa sulla mano della parte centrale dell’utensile ( quindi lato interno) mentre la mano esterna era solo di appoggio per accompagnare il risultato è quello mostrato nell’immagine.
Luigi, what you write is in my opinion a further confirmation on the problem of adaptation.
Having off-centered the tool, you went to work the areas that were previously partially reached, you have deepened the area a 3/4 of the diameter and in fact the connection with the median zone is now more continuous and uniform.I am not saying that the precautions you take are not right, I say that ( indeed Ronchi says so ) they were not sufficient to guarantee the maintenance of the pitch shape in all sessions, adaptation is necessary in each session, its verification comes from the analysis of the processing results, the only way to be sure of the good fit with the full diameter tool is when the technique ( performed correctly ) produces the expected result.
The good news is that now you don't have a sphere but a decent parable
, still missing to fix a bit’ of roughness in the center which so far has only been partially affected by the machining.
I would do some measurements with Focault, I don't think you are very far from the final parabola if the reticle you used is around the 4 lines / mm you are very close to it e, if the polishing is complete, the sphere at this point is not even needed…Sì massimo le tue considerazioni sono giuste la pece ha una densità che la rende idonea per temperature primaverili o tardo estive quindi autunnali certamente non per temperature basse come quelle di questi giorni; almeno dove vivo io fa particolarmente freddo. D’altronde non mi sono messo a ordinare Gugolz ed a rifare un nuovo utensile di pece perché il tempo mi avrebbe impegnato molto e in effetti tra tempi di consegna e la realizzazione dell’ utensile se ne sarebbero andate alcune settimane… Del resto in passato ho avuto occasione di lucidare con un utensile originario che allora era di vetro quindi già convesso con degli optipad sagomati ad ottagono ed il risultato era molto simile a quello che ho ottenuto con questa pece proprio perché non si amalgamano più di tanto sono molto rigidi e hanno un effetto come quello di una pece molto rigida, infatti cambiando tipo di manovra raramente ottenevo dei risultati differenti.
Comunque in settimana realizzo la maschera di Coudé dopodiché vado a vedere come sto messo..
Sì il reticolo ha quelle caratteristiche è quello che fabbrica LolliI made a mistake in judgment and I apologize for it… In the last image of Ronchi, to be in the “vicinity” of the parable of a 300/1700, the reticle used should have 5 lines / mm and not 4 lines / mm as I erroneously said.
In the following image you can see the display difference of the parabola of a 300/1700 with a lattice from 4 l/m ( at left hand ) and one with 5 l/m ( to right )
Beh quello di Lolli è un 4 per millimeter… io ho questo non ho chance…
Comunque in effetti ci sono abbastanza vicino. Considera che la zona centrale è venuta un po’ sfocata ma in realtà è lucidata è solo che non l’ ho pulita benissimo ed è rimasto forse un po’ di alone che ha creato quella zona diffusa quindi devo solo concentrarmi sulla zona tre quarti per abbassarla un pochino e poi direi che ci siamo
hello Luigi. The only caution I would add is a precaution to always lay a polyethylene sheet (Domopack) between pitch with cerium and encrusted mirror, and not allowed to come to direct contact.
And the more “sacred texts” They say that direct contact between silicates and oxides pitch, safe source of micro roughness, sometimes you can even see how iridescence on wet mirror and illuminated by a neon light.Moreover, even at temperatures “fresh” and prolonged contact time, pitch settles with continuity, and there is the risk of ruining the tool to only detachment, or not more rouscire to detach it and having to vex for separating objects losing the tool.
Leg, also in view of making the foucault test in a uniform temperature environment, You should try to adapt the ambient temperature to that of the pitch machining, because work in the final stage, a face of a mirror quite cooler than the, heating it in a more sensitive way only for machining on the one hand, It is an impediment that creates you sure failure in the glass removal, which means astigmatism during work due to that two sides of the mirror are more deformed than they would be to the nearest temperature to the working position, Whereas the tolerances are at stake millionths of a millimeter.
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