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Good evening
I see there are already some discussions on this,but I don't like to get among others,so I'm starting a new one. The main questions are 2 (just to get started
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As the first scratch I wanted to start with a very common glass,I found a glass factory that can cut the 19mm for me,to make a 250 or 300 in diameter it could go? Talking to the glassmaker he told me that one of his colleagues has the oven to glue them together and therefore double the thickness,have you ever tried?
Thanks in advance.hello Fabrizio.
And, with the 19mm glass today it is possible to reach the diameter 300 making a good cell verified with GuiPlop.As for the fusion of two disks to double their thickness, it is definitely practicable, (for some time now, Hubble Optics has provided mirrors made up of two disks anchored to each other by the general ramollimento in the oven against many columns of identical glass), but there was no experimentation, therefore it is difficult to say whether the resulting mirror can fall victim to internal tensions due to the welding process, such as to deform it at the moment of its weakening of a face due to the excavation on it of the curvature.
You should know how annealing and stress relieving treatments for glass work; and have the courage to try.
But the risk is there because the tolerances of making a mirror are the same 68,75 millionths of a millimeter, and an equally small deformation is perhaps possible…But it could turn the mirror into an expensive paperweight.
Ok understood
Now I do it like this,I get cut 2 300mm of thickness 19mm and in the meantime I'll see if I start to understand something,already compared to mine 155 this summer will give me much more satisfaction. Later, if the passion continues and above all I succeed in the work, we will face more important dimensions and we will see how to do it.To make you cut the two glass disks, keep in mind that 5mm should usually be added to the nominal diameter of the mirror (example 300+5), which are intended for the circumferential chamfer, which must be kept in mind for the duration of the processing, in order to avoid chipping at the edge.
Good evening,
ordered the glasses and the Carborundum from 60 to the 1000.
I took two 310 glasses, but also a big bag of plaster for molds,What do you recommend for me as a beginner,Making a tool or working with two glasses?Absolutely work with the two glasses. (My thought is that, for what a 19mm calcium-sodium glass costs, especially for a neophyte it is not convenient to look for other solutions that would be very experimental and quite meaningless). THE FIRST TIME IS BETTER TO GO STRAIGHT TO THE MIDDLE, that the road is still unknown.
I totally agree with Giulio, furthermore, the two glasses offer more control over the regularity of the surface being worked on right from the early stages, polishing is achieved with a good perception of the quality of the sphere simply by observing the uniformity of the distribution of air bubbles in the abrasive mixture between the glasses.
Perfect thanks,Today I got the glass and yesterday I received the Carborundum bags,Now I have to order the cerium oxide,I agree Matteo,how much do I take? I read that I should need about 600 grams for the 310 mirror. Somewhere I read that I could replace it with aluminum oxide,you confirm me?
Aluminum oxide has good polishing power, however it is difficult to find it with controlled grain size, ( and when it is found the price increases ) which means that between normal granules of average size of two microns suitable for polishing glass, there is a significant percentage of larger granules which generate lines and grooves on the surface which are then impossible to remove except by grinding and carborundum.
Furthermore, aluminum oxide is a not very tough material, if you observe the granules under the microscope you can see that they are made up of cutting and sharp edges but that only after a few passes they round off and lose their abrasive and polishing capacity. Therefore we are forced to have a greater replacement and use compared to cerium oxide.I believe for one 300 Suffice cerium oxide for less than half a kilo….(maybe even alone 250 grammes)
A “span”, a flat kitchen spoon is used, diluted in a little water just enough to make it creamy and spread on a mirror or utensil with a brush.
Usually enough for a work evening (and sometimes it moves forward, and is reusable the next day, only if it does not lose its smoothness. This is recommended to make the dilution in a formerly homogenized baby glass jar, hermetically closed at the end of the work). Otherwise wash and throw away the residue to avoid encrustations which cause the particle size to vary..The cerium oxide, unlike carborundum, it becomes embedded in the pitch, and therefore only one fraction is lost. That's why it lasts a long time.
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