- This topic has 170 replies, 5 voices, and was last updated 5 years, 5 months ago by
.
-
Posts
-
We start with the creation of a primary diameter by 300mm with a focal f / 6.
I will use this thread to progress, advice, errors solution etc. then feel free to criticize, to advise, help and intervene when and as you see fit.
The blank in question is a borofloat33 produced by Schott and has a thickness of 25mm. As can be seen from the commercial name this is a borosilicate glass that compared to classic calciosodico a lesser extent alters its size when the temperature changes and this should allow me, during parabolizzazione, It can make measurements and corrections without having to wait for the biblical times of calciosodico.
To achieve a 1800mm focal I need to get a 3,125mm arrow.
Following an interesting article by Dave Grennan, passatomi by Giulio, I tried to create a tool consisting of a diamond disc from 115mm to try to get a more rapid sbozzatura. However this path for me, at least at the moment, It did not work generating only isolated lines on the blank surface, so I decided to temporarily dismiss it and go classic ceramic utensil full diameter.
I put still pictures tool created by me:
The tool diameter full that I created is made up of dental stone type IV and squares of porcelain stoneware drowned in casting. I forgot to attach the pieces with glue stick and then have a little moved but I can go well anyway. I then made a kind of channeling with the Dremel.
At this point I then well-blunted the edge of the mirror and tool, smoothing the sharp corners of the ceramic to avoid sbeccare the blank.
Now I pass the chordal grit 80 but I want to make sure that the tool is a decent back-up.Past chordal begin to bear fruit, The tool works well and the center of the mirror slowly begins to fall. If I can find a tool defect made in this way refers to the increased consumption of carborundum, working face-up, inevitably it tends to disperse in part drains.
'Ll scratch a few more hours then I'll start with the arrow measurements to assess progress.Bravo Stefano, a great start ! According to me for this job the tool full diameter is the best choice.
To limit the dispersion ( and increase effectiveness ) abrasive can reduce the amount of water, that in any case it should be very little commissioning. If you already use the abrasive almost “dry”, do not be afraid to overdo the pressure. When you hear a noise “terrible” scraping it means that you're digging well !Hi Stefano
In my opinion the tool you could leave him without the grooves at least until use of the grain 400.
In fact, with the biggest trouble you just dig without worry that much to create scratches on the surface. I used a tool similar drowning in the plaster of the pieces of glass with a thickness of 20 mm and for the excavation has gone very well. Since the grain 400 in my opinion it is good that the part plaster does not go directly in contact with the mirror as though aligned more tender principle of the glass can still create micro grooves (perhaps due to the fact that if the cleaning is not perfect when changing abrasive few grains may remain stuck in the plaster?) quite boring that would force you to go back to the previous grain. Furthermore it agrees perfectly grind the edges of each tile to prevent detaching of the micro chips that would be deleterious.
However overall the tool you've done seems well built, I believe without a doubt the best of the diamond blade that even if he ran as fast to reach the desired arrow, He would still forced to build a tool adapted to the excavation made in order to then continue with the finer grits.
In any case, I know that I follow with interest your job, because personally I am currently unable to continue the work of my 300 mm. In my garage now it is not too well and to give you an idea of why I attach a photo .......
Thanks Massimo, I started to take a little’ his hand and saw that just wait until the channels are a bit’ saturated and use little water to get the best performance. Gim, the grooves got them right away because in a couple of items to make them said to prevent mirror and tool incollassero or rubbing it becomes too “psstoso”. Honestly I do not have the experience to evaluate it from a technical point of view. The plaster at the moment it looks nice sealed, in the sense that when I clean the tool with the brush no trace remains of the grains. Most likely you just have to be careful that there are no small holes or cracks on the surface and seal them in case, but it is an issue that I will discuss later… One of the many I meet.
At the time I worked a couple of hours and how I came to 1,09mm arrow so are the target -2,04mm.
However, in any articles I had read how tiring the grattavetro! In the summer, it is devastating
I'm working on 30 and passes degrees, I stripped to the waist and with a band on the forehead, It looks like karate kid
In this heat working pitch imagine it is very complicated without an air-conditioned room. But so much when I'm at that point it will already be fresher
I'm really very happy to read your comments on the exchange of your personal experiences and thoughts, because this is the real educational usefulness of a set Forum in a specific blog !!
They are exposed and subject to comment REAL THINGS, fruit of knowledge priopria.I agree with the thought of GIM and with your Stefanosky, and I emphasize that the real fatigue is known to be precisely that of the excavation dela curve.
Once the desired arrow reached, continue the work by applying the less athletic races 1/3 Diameter c.o.c, that do not need to exert pressure(*), and are very little efficient in the excavation, but that lead to generate and to maintain the desired sphere to the desired depth of arrow, extending up to the edge of the mirror during the whole phase of the surface puddling, with abrasive grit away finer way.
(*) Recalling the known fact that with the races 1/3 D c.o.c, We have three possible actions:
1) With the mirror in his hand and the tool on the bench It deepens the center of the mirror, leaving untouched the surface to be 0,7 D to the edge; while conversely:
2) With the tool in his hand and the mirror on the bench working only the edge leaving the center intact.
3) Alternating between the two positions driving, and “ball”, corrects, and it maintains the arrow and desired sphere constant.A certain pressure can be exercised only in cases 1) e 2) to recover mutually the ball a little arrow (cone action 1), or excessive arrow (with the action 2). while maintaining a reached arrow does not require pressure but only dragging (and patience) to generate the desired sphere… the more the pressure-free and accurate drag applied through the edge of the bustling glass, with the progress of finer grits…(In fact, by applying pressure to one you run the risk of making “game over”, flaring too much or too early in the ball parable or worse in hyperbole, and having to work for a long time racing 1 / 3D c.o.c without pressure to resume the initial sphere).
In summer the pitch black #55 e #64 ..se ne va da sola “about his business”, as it is seen in the tool of the image posted by GIM.
Scratch Scratch I realized that, in my case, the most profitable procedure is slightly wetting the tool and distribute the abrasive on its most outer band. On the glass nothing, ne ne abrasive water… In this way the carborundum used goes to work exclusively in the area of interest along the entire circumference of work while distributing the abrasive on the glass this was mostly dispersed in the first quarter of a turn making it less effective than the rest of the work.
If in the meantime the abrasive tool along the circumference dries a little too just a sprinkling of light water and again.
The arrow now measures 1,84mm 1,28mm then missing from the theoretical target, actually I go down a little bit more to be able to work primarily with the tool over so as to use less abrasive… let's continue. 
Sorry Stefano I have a question to ask.
In your last speech I read that you lack even the excavation 1mm par reach the desired arrow, so I suppose you're using carborundum grit 60 or at the 120.
Now what I do not understand is that in the picture you've posted, unless I do not have hallucinations, you can clearly see the reflection of the ruler that you place on the glass in the works, as well as the depth of the excavation. Now I saw that I came to use the grain 1200 that gave me a fine satin finish but without even the shadow of a reflection, explain to me how you did it? What escapes me? Well you see the reflection because the mirror was slightly wet, otherwise the satin finish would not reflective since I'm using 80-grit… So everything normal
https://www.youtube.com/watch?v=_gd-is8DBUQ
With past chordal I reached the required arrow, and tomorrow I will begin the phase of regularization of the sphere using past 1/3D CoC, past that accompany me also in the subsequent processing phases with abrasive via finer via.
With the Dremel in the meantime I redid the channels along the outer end of the tool since the past chordal it had gradually decreased the depth up to delete them at several points. This fact caused a worse performance than the abrasive and a shorter duration of “annoyed” works “kneaded” much earlier and it forced to clean more often utensil and glass. Reopened channels everything is back to spin smoothly Hi Stefano…
the progress Congratulations…
you see that you have taken us out and that you are very safe when handling…I see myself in this video…
It will follow with interest future developments…good job…ciaoI'm using the past 1 / 3D is but I have a doubt… I read that some start with chordal with a lateral offset of 40% until the 25% arrow, then to 30% until the 50% arrow, then to 20% deviation of up to 75% the arrow and when you get to the desired arrow start with 1 / 3D coc. I, as you, I kept the percentage of deviation always around 40% until the arrow, only after they started with 1 / 3D. Now I am clear with a border of about 15mm not work that should gradually dwindle with 1 / 3D. What are the differences between these two techniques? Someone has tried both?
I take this opportunity to expose another doubt… As you can see from the picture the two highlighted areas from the beginning have almost never been touched, unlike other areas of the border, even if a small part, They were affected by the work as much as to become satin. of a homogeneous glass processing Safe, what this difference may be attributable? Mirror not perfectly paved originally? Continuing to work it is something that will fall into place if? Trying the arrow by placing the bar on the parts marked this turns out to be less than about 1 tenth compared to the same measurement made on the other two zones. In fact Measurement 3.05 mm instead of 3,15 the other measurement.
Hi Stefano.
What you get with a chordal passed like the one that appears from the video can deepen very quickly the center. Unfortunately, that kind of past does not provide some good ball. If you own one spherometer measuring the radius of curvature at the center and near the edges. You will notice immediately that the center of the measured radius is shorter than the edges. Moving from the periphery toward the center gradually you reach the desired arrow would allow him to have a more regular ball immediately. In my opinion anyway to bring everything back in the right track just continue to "scrape" with the canonical past 1/3 CoC remembering to often exchange the tool position and the mirror so as not to exceed the desired arrow. Sconsigliatissimo, always in my way of seeing, switch to finer grits before the spherometer indicating a good evenness of the surface, allungheresti only the processing times. This should also allow you to eliminate irregularities at the edges.
Hello everybody
- You must be logged in to reply to this topic.