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Hi Massimo, welcome !
Congratulations, beautiful and interesting your creations, it will be a pleasure to read you
!Ma no, the size of the blocks do not count, must not be the same, if anything should not be more “low” or more “alti” with respect to the contact surface.
Average to run a good polishing how long it usually takes?
it is better if I tell you
hi Luca, from a photo it is almost impossible to tell if the fit is good, It considers that a contact difference veneer / mirror of a tenth of a millimeter Center / Border is not a good fit. A couple of ways to check:
A- It should be noted the consumption of squares ( the surface becomes white in contact with cerium ), If after a session consumption is uniform and the color tends to lighten over the surface then it is ok, otherwise you can see which are the areas that are not in contact because they maintain the original color.B- if the mirror is polished and transparent on the back, you can try to put the mirror above and below the tool, after putting the mixture of water + cerium with a brush on squares. The squares in contact do not create air bubbles if not to the same edges quadrotto, while those that are little in contact, forming a central air bubble that moves when you move the mirror ( as the air bubbles of the levels ).
to answer your questions:
1-Not essential but help distribute the abrasive evenly, avoid overheating of the patina during races, help to improve the smoothness of reducing the friction and therefore the force required to move the tool on the mirror.
2-Too much water reduces the effectiveness, also too abrasive… The density of the mixture must be similar to a very fluid cream. The right mix is easily, it is prepared separately in a jar, if it is too dense water is added, if it adds little abrasive. Using a brush and put it on the glass or on the coating, It must be similar to the mixture of the colors with water “watercolor”.
3-only in some particular cases and when there is a need for processing that requires it, normally it is sufficient the weight of the tool. Rather, You must be careful not to put pressure on the board during the races. If you just need a little’ additional pressure, then it must always be applied to the center and with moderation.Chapters that if you do not know French, You could translate into Italian using "Google Translation", choosing the language French origin, to be translated in the Italian, and then clicking on "Document", to indicate one at a time PDF chapters downloaded in French.
Or, more simply, you can find the same things here on Grattavetro, with translation of texts and videos from French by Giulio Tiberini
(Julius has written so many technical books and popular, and not only here on Grattavetro, it becomes difficult to remember them all even for the author…
)Luca sorry, I had missed the grid, right Giulio… in fact it is too small and also the grooves must be more wide and deep to allow the patina to yield and conform to the shape, otherwise as I said before, It remains rigid even with application of a high weight, sorry…
And, the color of the patina now I like,
It should be fine and I agree with Mirco, I would try with hot water. If the consistency / hardness is correct cold patina does not deform even if we go up on with both feet ( I did it several times ) But just heat it up a bit and you can not have a good fit. What happened to you it is normal, to the point that I, even more I try to give it the shape immediately after the merger casting, especially on a tool 30-40 cm.
Is’ hard to catch the right moment and most of the time is wasted effort because the patina temperature quickly cools on contact zones, and then you can not make them give in to what it takes, so then the real patina adaptation / mirror you get the warm patina .
Once you reach a Remix soddifacente, there is no need to add more even if it is melted again.
Besides the oil, as Mirco says, the network and also the mirror can be wet with soapy water to prevent any bonding.Thanks Luca
The temperature you will have in your work environment is optimal, I believe you can try with quantities 65-35 for pitch and beeswax, always with the minimum quantities of turpentine and linseed oil.
However, I would do a test before casting the casting on the tool.
The “nail test” it is very immediate, it can also be done on a small sample of the casting without necessarily having to build the tool first.
Just be able to leave the nail groove on the patina, doing a little’ pressure for a few seconds.
The furrow generated must be seen but at the same time the surface of the patina must not be deformed or yielded under pressure.
If in addition to the nail imprint, there is a failure is obviously too soft, the amount of turpentine should be reduced and secondly, that of beeswax ( or add more rosin )
If you break your nail, but not even talking about the furrow then turpentine is added and there was bees.Linseed oil increases and uniforms smoothness over the entire patina without limiting too much the friction that is necessary, but it should be used with caution.
hi Luca, welcome back ! I don't know what to say about abrasive paper instead of silicon carbide, I have never used it but the perplexities that Giulio said a few posts ago are a bit’ mine too…
For the patina of pitch instead, I believe you will immediately notice the lack of beeswax as the friction that will develop in contact with the glass will in all probability be excessive.
The right mix of components is a delicate recipe, which works in a certain temperature range.But I understand you, I've always had a bit of an approach too’ “subversive”, not to say ” Taliban” to consolidated working techniques, in some cases it led me to guess new ways which then proved effective, but in most situations, I would have been better off listening to the texts we all know
So my advice is to try ( in winter ) a patina with bees (35-40 %), rosins (60-65%) , turpentine (little, less than a spoon ) and also linseed oil ( a poor cap of the package ), you will see that it works much better and faster !
hello Mirco, I saw that discussion… what a pity, sorry even now, It was really a great job !
About Plop, what do not understand is what thickness should be considered for the calculation. Pretending that the meniscus is a blank plan, to have almost uniform thickness should set a radius of a few dozen meters. Otherwise, inserting the real radius + thickness, Plop “thinks” I have left only 1,5 millimeters thick at the center … Thanks Giulio
But I think that the cell will magazine, perhaps it serves the aluminum of suitable thickness in place of wood, especially on the bars that support the triangles, otherwise you can not load weight on the tool during machining because flex at the ends, slightly but for the moment should "light" to go without relying too much on the tool… I do not know, it is better to give more thickness to multilayer or go directly on aluminum ?The meniscus is still out of the oven quite battered
( optically speaking ) , I do not deny that before starting I thought "how nice it starts directly to regularize the ball with patina and cerium" 
but the illusion is very little time.
Astigmatisms and many areas outside figure with a "p / v" estimated slightly lower than the millimeter.
But, I enjoyed it possible to "map" the mirror during processing with 80, at some points when the tool is "impuntava" in the moment that touched the highest areas and in other slipped away…
This was the situation in the first passes with 80, so I had to first return to the figure symmetry, working on the center median zones, trying not to change the overall depth if not strictly necessary.
Now the mirror is spherical ( relatively all'abrasivo 80 ) with a good symmetry up to 4 cm from the edge. At this point you can extend the processing to get to regularize the border, and then around the meniscus.
When the meniscus, I would say that in any mechanical disc of any printed material or limp to "bowl" mentenendo the same original uniform thickness, stiffens.
But in fact! It is what I think so too… Here it would like Mirco that gives us a nice calculation on the deformation of a meniscus, so let's see if we're right and how much
Giulio, Waiting to understand how to design / build what you suggest
, I built a cell "on the fly", very safe, just enough to rest the meniscus will start to see what and how you will be working. As I thought after a glance, just mirroring myself on the glass, despite the softening of the mold, the surface is far from being a sphere. At first it seems a ball, perhaps as a "piece of furniture" could also go through spherical, but for what you need us we are far.
I wanted to build me a suitable tool, but by chance I saw that I had the tool of 300 mm has almost the same curvature of the meniscus. By supporting the tool on the meniscus the edge remains raised approximately 1 mm.
But even the meniscus gave the impression of having a more pronounced curvature in the middle and not at the edge, as if the central zone had managed to fall by gravity to the mold during the softening, better than he had the edge.So I thought the ball was still standardized starting dall'abrasivo 80, better with a tool a bit 'more "curved", so that the various zonal curvature of the meniscus would soon be standardized with that tool, which would be completed starting from the center and not from the edges, without, however, altering the overall arrow ( almost ).
In the picture, the "improvised and temporary cell", of simple multi anyway after hearing that he thought Plop. To the right of the surface after 2 dried with 80.
It is seen in fact that a crown of about 4 centimeters to the edge, It remained lucid because it is not achieved by processing. The center is "touched" by the tool while the median-outer zone is the one that has longer need to be processed and that further undergoes the action of the tool.
After three sessions, the tool is adapted to the meniscus for a little more than half of the diameter, but the progression seems to be fast enough. In fact, from the first to the sixth dried, the contact surface between the two panes is passed from 50-60 mm to initial 160 mm dell’ultima.Thanks Mirco, In fact, the first problem is one of those where your opinion and that of Giulio might be enlightening.
Put simply: where we caspita support him the mirror for processing ?”
Said in a less simple: the cell “standard”, that designed with Plop, It may be valid also for a curved support surface ? with which criteria can be evaluated where and how to intervene to modify / optimize a standard cell to host a mirror meniscus ( moreover thin ) ?
I also thought of making a plaster base, obtaining the mold directly on the meniscus, but this, assuming it is effective, only the problem of shift at the end of machining cell. So while I started to build a normal cell, as if it were the mirror plane, then.. let's see what happens, something we invent And, as he said Giulio is a diagram with fire Nasmith, usually applied to Cassegrain configurations that allow the secondary obstructions smaller and more compact overall size.
In this case, the value of the obstruction is given by the position of the secondary plan that, however, it should take into account two other aspects to determine the actual size of the obstruction and the secondary same:
1-CPL, ie the full light field, namely the area on the focal plane around the axis completely optical “illuminated” by reflection. Being a photographic tool, CPL will presumably have the dimensions of the sensor that will be used, to avoid “vignettature” moving away from the optical axis.
For example, for a CPL 15 mm in the secondary drawing, in that position, You must have a diameter of 186 mm
2- HOOD: unfortunately a configuration which positions a tertiary that “look” directly toward the object framed, in the same way the primary, It brings light and unwanted reflections directly into the visual field, thus it must be provided for a hood system for all the mirrors that allow the reflections only for the primary optical beam. This will result in a further increase in actual obstruction.Hello and welcome ! Surely the problem of the plane of the mirror construction is quite complex, to the point that I do not see the convenience to perform a similar processing except for pure purpose “didactic”, ie to evolve and refine his knowledge in the construction of optical reflection.
Paradoxically, working planar mirror can be even more difficult than parabolic, area measurements should be made for interferometry, and it takes a proven technique of working.
I believe that as long as you remain on non-excessive measures, should buy it for two reasons:1-The economic cost is definitely lower than the constructive effort of “do-it-yourself”
2-Buy ( at least ) a plane mirror secured on the surface correction, means having a “caliber” to be able to independently carry out other flat mirrors that will be tested on the same gauge until it reaches the same optical correction.And if the decision is, however, to still groped, you can talk, we are here for !
I also rifletterei on configuration with three mirrors, which inevitably leads to not simple collimation problems. ( I know something…
)
Moreover, To lower the height of the eyepiece in a Newton, Also personally I would estimate the configuration “low riding”, with only two mirrors, as well described in a draft Giulio.Sincere congratulations, un lavoro eccellente! se Riesci a fare un rochi dell’intera superficie possiamo valuare anche la qualita’ riduardo rugosita’ e stato generale della superficie, potendo escludere cosi’ anche eventuali problemi non visibili al foucault come errori locali ed anche capire l’entita’ del possibile bordo ribattuto.