Parabolizzazione mirror 300F3,8 (part 2 of 4)

Re: Parabolizzazione mirror 300 F 3.8

It is well to remember that the most difficult part of the Foucault test is just the start with the certainty of having identified the focal point of the area 1, in which unfortunately the shadows vary from infinitesimal amount over several revolutions of the micrometer, making it highly uncertain individual assessment.

In fact, the progression of the shadow in the focal point of any area, It should not come either from right, nor from left, but from a hypothetical circumference, closing in gray as a kind of camera diaphragm.

The trouble is that if that first difficult measure appears incorrect, drag the software in an incorrect assessment of the quality of the parable, because that in all other areas of the tolerances are gradually much more restricted compared to the area 1.

There are some ways to kick start. I (Perhaps I have already spoken) I use my own method (not infallible), which consists in going with the tester's cursor position in a well intrafocale, I see the shadow of the knife entering frankly right, with a certain progression of the shadow as the blade enters the beam of light. then I take note of the reading of the micrometer.
Then I move in the opposite symmetrical position extrafocal, until I find the point at which I judge the same progression darkening, obviously with the shadow, however, coming from the left.
I also read here micrometer, and then find the middle point subtracting from this value the previous reading, and dividing the result by two.
then it moves the meter reading on the blade until the calculated value micromento.
That position is more likely to be that of the local fire 1.

Re: Parabolizzazione mirror 300 F 3.8

It Giuliot, You had already decritto this methodology for the identification of the area 1, method I decided to apply to measurements:

I must say that the webcam is a great help, because when you are in doubt between two values ​​close ( almost always ) you can take pictures and compare them also with any photo software by measuring the difference of the gradients in the two sectors in the shade, all without leaving the station.

I attempted corrections, there is some mistake that I make but I can not figure out what.

I'll explain:

This is the Ronchi compared with simulation:

Click on the link to enlarge

http://s26.postimg.cc/srwxmyb6h/Picture_941.jpg

Click on the link to enlarge

http://s26.postimg.cc/vna0ttf6h/unnamed.jpg

As can be seen the difference is obvious, especially for the depth of the center with respect to the peripheral zone

These related measures with Foucault
zone 1: 0.10
zone 2: 2.10
zone 3: 4.20
zone 4: 6.90
zone 5: 8.80

report:

Click on the link to enlarge

http://s26.postimg.cc/o9umuuv4p/image.jpg

Click on the link to enlarge

http://s26.postimg.cc/cjgpdh2c9/image.jpg

He Foucault test , among other things, tells me that after these corrections are almost at the limit for the overall draw values, measures of which I'm pretty sure ( with the precision limited to 1/10 ) having them re-checked several times .

The two tests do not seem to get along, if I were to follow the directions of deepening the center Ronchi definitely go out with the draw values, unless ( What more likely ) not're doing something wrong…

Re: Parabolizzazione mirror 300 F 3.8

Ciao massimar I see you're working hard. You mcrometro mounted on the longitudinal movement of the Foucault ?

Re: Parabolizzazione mirror 300 F 3.8

Ciao astrotecnico, it's true I'm working hard using every minute of free time and, as you expect, parabolizzare a short focal length is not simple ( at least for me ).
I have not yet installed the micrometer, I'm using the native dial meter that would allow measures 0,05 mm , the problem is that I have not yet developed adequate sensitivity for this precision, for now my level of measurement accuracy is in the order of 0,15 mm, level below which the doubts are more certainties. Certainly I am going forward be able to refine the accuracy of readings.

In addition, the sub-diameter has the disadvantage of being much slower than the full-diameter, and to be “healthy carrier” as well as zonal errors also roughness which then must be connected and standardized, however, it allows a more targeted intervention without excessively annoy the adjacent areas.

Luckily, in addition to your guide, there is the constant and inexhaustible support Giuliot It can also unlock the hidden secrets of these techniques, without which it would have been a mission impossible.

Right now I'm trying to shorten the fire area 4, which is the most out of tolerance, then to increase the curvature in that sector without changing the area 3 , how you will ? we will make it ? mah… :hmmm: I know that the next operation will be the return to the sphere No. 1 :)

Re: Parabolizzazione mirror 300 F 3.8

With 0,15 mm readability only are you confused ideas. It is necessary that you manage to get ahead. Or use for now only Ronchi.

Re: Parabolizzazione mirror 300 F 3.8

I still need some’ training, I'm sure the accuracy of readings increases with practice, I tried yesterday and insisted readings to 1/10 and I am pretty happy, ( only quality readings, some of the test results’ less :) )

Re: Parabolizzazione mirror 300 F 3.8

therefore, coming to your mirror, try not to go to the ball and see if we can fix.
Notwithstanding that, however, we somehow need with better accuracy readings. The problems you experienced on subdiametro are absolutely common. Nothing new, then consulates. Is’ so. And then F3.77 is duretta …
But let's understand a few things:
– With that you're working subdiametro ?
– Hand guess ?
– On the turntable with motor or by hand ?
Then we decide now with what we test while you make the sistematine, admitted that succeed !

Re: Parabolizzazione mirror 300 F 3.8

Thank you astrotecnico, It is the kind of help that I hoped, it is difficult to decide what to do, It is likely to do the wrong thing …

here is the data:

subdiametro in 125 mm ( 42%) ( with a pitch patina “lucky” that fits perfectly )
absolutely handwork !
rotation operator ( that is me :) ) constant around the table

the problem is that the last test I made other corrections, rather prolonged, I believe they have worsened the situation.
Tonight I will attempt the test measures 0,05 mm as accurate as possible, then the public the results.

Re: Parabolizzazione mirror 300 F 3.8

Your diagnosis on too draw between internal and external (with the measurements you have listed) it is apt.
I, from the top of my little EXPERIENCE, in the case of your measurements, I would definitely come back to the ball, because with that data (and with reference to my spreadsheet for one Ø300 mirror with focal 1120mm and mask to areas from 67-94-116-134-150mm) have an edge retorted in area 4 e pure 5. And with that ball and chain I would not be able to recover anything.

This suspicion is confirmed by the fact that I can even simulate different values ​​as a result of appropriate corrections hypothetical ... But with the edge retorted none of these can lead to a better lambda 2…If I'm not back in a backward.

Note then that with those data, the single zone 1 its rays converge in the diffraction mark Airy, while the other areas do not satisfy the criterion Couder on the transverse aberration to fire (therefore not fully participating in the formation of the image, and thereby providing a poor contrast thereto).

I in your place then I would do so:
– At first I go back TO the ball "digging" a little predominantly Area 2 (which it is "short", and draw 2.1 expected to rise to 2,8)... in the strong hope that also the adjacent area 3, soar from draft value 4.2 that near 4.65, not to mention the next zone 4 that would be ideal if it came down to draw value 6.8 (but since it can not just go down, unless you return back again towards the ball, might as well stay 6,9 with little damage of a lambda 5,7)…but the zone 1 and 5 NOT must move absolutely.

With those hypothetical values ​​draw (0.1 2.8 4.65 6.8 8.8) simulated on my spreadsheet; values ​​which, moreover, from a practical standpoint, however, are difficult to obtain (if no proceeding in small steps and consequent controls), You would have completely overturned the omelette. Getting back a horizontal edge, together with the fulfillment of the criteria Couder, and to a lambda 6.3 (obtained by setting one focal deviation with the value 2000 to improve the P / V ratio)….. which would lead you to spend 130 € aluminizing "enhanced" ...... .With a see you next "scraped". ;)

Of course these are my thoughts “land land” and freewheeling, dictated by what we have so far managed to learn, knowing that “from saying to doing”…….

Re: Parabolizzazione mirror 300 F 3.8

Thank you Giuliot, a very useful explanation of possible strategy, unfortunately after the latest fixes the situation has worsened and I think will agree to return to the ball…

A little bad, I had some claim to realize the parabola f 3.77 at first try, it was just luck, and relying only on luck we learn very little.

I can say that in this first round I field tested the action of various techniques with sub-diameter, I understand many of the mistakes ( not everybody ) and I feel much more aware of what you will have to make the next attempt.

However some success has been achieved, for example, I am very satisfied with the absence of surface roughness, I realized how “attack” and then uniform the surface even with the sub-diameter , which until recently it was in the top ten of the first places ” how the hell do you ? “

In the image of the last Ronchi you can clearly see the surface “smooth”:

Click on the link to enlarge

http://s26.postimg.cc/o4173rnrt/987.jpg

These are relative measures :

1.15
2.80
5.45
8.25
10.8

I had tried to bring the ball towards the intermediate zones trying not to touch the extreme zone, with past between the center and edge in order to dig deeper on the intermediate zone:

Click on the link to enlarge

http://s26.postimg.cc/aoe6ebfa1/411.jpg

I insisted too long sessions with dramatically changing the shape.
As can be understood from measures… I missed the train, I better wait for the next one :)
They are beyond the parable, beyond the point of no return, astrotecnico He was told to wait to return to the ball, but he had not yet seen these results.

Re: Parabolizzazione mirror 300 F 3.8

The problem is that for working with subdiametro it takes several, based on the extension of the area to be treated. You also get to use the tools to be a couple of centimeters or less in diameter. However, with those six measures unfortunately already out and recovery is arduous. So you have to go to the ball. I see no easy solution other.
As another thing I can tell you with subdiametro working well to machine, also maybe just having the plate of the rotating support. Turning around the mirror is easy to make mistakes. Moreover, fundamental, with subdiametro need to do frequent checks.

Re: Parabolizzazione mirror 300 F 3.8

Well, It returns to the sphere, What I had already started during the weekend, this time calmly following the “key points” of deabis, first of all: if you do not have fun, stop !
I tried to paste the full diameter patina ( that had come off completely remained intact ) with an intermediate pitch between casting and tool patina.

The operation appeared successful, apparently , but when using I realized that did not reach a uniform adaptation, patina seemed “hold” adaptation and deformed between sessions.

after a few sessions this was the tragic result :spaf: :

Click on the link to enlarge

http://s26.postimg.cc/5ccrg9r89/Picture_953.jpg

then I went back to the sub-diameter, despite the many disadvantages , There I am fine, better than with the full.
Given the type of “damage” I applied this type of sweeps 12 sessions 20 minutes, checking often,

Click on the link to enlarge

http://s26.postimg.cc/9ziti1el5/corr1.jpg

this is the sequence of each Ronchi 4 sessions:

Click on the link to enlarge

http://s26.postimg.cc/tvesxkvmh/ron_3.jpg

I have yet to give a sprucing up to the edge and then start the new parabola, in the meantime also prepare another sub-diameter ( 30% ? )

In this regard I have some questions about Foucault:
– if you use a mask with the area 1 central split, that magnitude must have this division ?
– how it changes the numerical set-up of the effective radii of the zones , should be indicated for the first zone the inner radius and outer as for subsequent ?
– It can be used the mask in this way ?

Click on the link to enlarge

http://s26.postimg.cc/dmyko3ms9/couder3.jpg

I wonder why I have seen that by the mask leaving free the upper and lower areas of the mirror during the test, you see the shadow feed profile which helps in the evaluation.

Re: Parabolizzazione mirror 300 F 3.8

Quote:

massimar (write 721102) … if you use a mask with the area 1 central split, that magnitude must have this division ? – how it changes the numerical set-up of the effective radii of the zones , should be indicated for the first zone the inner radius and outer as for subsequent ? – It can be used the mask in this way ?

1) You can certainly use the mask with the Division using the fact that usually the software that calculates, take account of the central hole that could have the mirror…and if you have the hole but pretend it, everything is equally well. ( And the software does not upset the progress of the shrinking of the areas to the edge of the mirror).

2) In the calculation of the mask it counts the centreline of the areas that go to draw, ie the distance from the mirror center of the area under examination.

Re: Parabolizzazione mirror 300 F 3.8

Quote:

Giuliot (write 721158) 2) In the calculation of the mask it counts the centreline of the areas that go to draw, ie the distance from the mirror center of the area under examination.

Giuliot, that's what I did not understand, the area is divided 1 It changes the centerline with respect to the same whole area “perforated”, so I have to change the value that the software sets the default for this area ( inner radius = 0 ) ?

Re: Parabolizzazione mirror 300 F 3.8

Quote:

massimar (write 721102) Well, It returns to the sphere, What I had already started during the weekend, this time calmly following the “key points” of deabis, first of all: if you do not have fun, stop !

Wolf in the tale!
And what do you think: who is not taking notes? :D

However confirm: slow and inexorable, Also Deabis proceeds, FUN, towards perfect sphere on which to build a dignified parable (but in this I will have my teacher in the flesh…….stay tuned………..:ok::D..).

Re: Parabolizzazione mirror 300 F 3.8

Quote:

deabis (write 721166) Also Deabis proceeds, FUN, towards perfect sphere on which to build a dignified parable….

no doubt :ok:

The only caution is that if you also take notes from my post, it would be better to write on, I’ title, “notes from massimar, or: everything you should not do “ , otherwise the dignity of the parable see it at risk… :D

Re: Parabolizzazione mirror 300 F 3.8

I believe that your current “difficult circumstances” is due to the transition to work with tools subdiametro (experience inter alia useful in perspective of a job on diameters > 12″). In fact, I'm curious to see if they meet similar difficulties, seen that I will use until the end of tools with a diameter equal to the mirror.
I rejoice in the fact that we are putting together a nice little’ useful experience to those who in the future will undertake’ this road…..:ok:

Re: Parabolizzazione mirror 300 F 3.8

Quote:

massimar (write 721163) Giuliot, that's what I did not understand, the area is divided 1 It changes the centerline with respect to the same whole area “perforated”, so I have to change the value that the software sets the default for this area ( inner radius = 0 ) ?

Simply for each window to do outer radius minus inner radius and divide by 2, and add the result to the inner radius.
This mode is still valid.
The software you use to realizzRe the mascbera should take this into account, asking if the inner radius of the area 1 should be zero (for a mirror hole in the center), or the diameter of the hole of the glass ( real or hypothetical) that the mirror could have.

Re: Parabolizzazione mirror 300 F 3.8

Thanks Giulio :ok:, Now I understand ! I verified, the software asks you to set the values ​​of the area 1 exactly as you said, while for the subsequent zones it can only be changed the value of the outer radius.

Re: Parabolizzazione mirror 300 F 3.8

massimar, in principle, to work a 300 of sub-diameter tools it takes at least three: a 125, a 62 it's a 31 millimeters. The basic concept of working with sub-diameter is to consider the surface divided into a series of concentric annuli,which are then ultimately the eddy zones, within which work. The annuli therefore should be brought within tolerance within the ML diagram. Also consider that if the side jobs, how are you doing, excavations practically a groove on the surface. But when work on the radius before you act little or nothing. So the depth of the furrow can adjust it by working more or less sideways, besides regulating the past. Moreover, to regularize the surface, devi “screstare” generated crowns. I hope I explained and not have you confused ideas ……

Re: Parabolizzazione mirror 300 F 3.8

astrotecnico, you explained very well, as always, not only do you have me confused ideas, but in a few lines you have answered a series of questions I had in mind, thanks because finding explanations ( exact ) they enter into the merits of this type of processing is also rare and difficult sailing overseas! :ok:

Re: Parabolizzazione mirror 300 F 3.8

I would say that with the ball we:

Click on the link to enlarge

http://s26.postimg.cc/p1qwycqop/RON_3.jpg

surely you can do better, the sub-diameter still has the potential to be expressed , there is a hint of depth in the central area, but I think as a starting basis for the parable ( 2° round ) will be fine, che ne dite, I can go ?

Another difference I noticed with the sub-D. It is that there is a configuration “stable”, there is the analogue of 1/3 COC full-D. which leads to a stable sphere. Once you achieved a result, if one insists with the same pass it goes beyond the figure reached, to new and unpredictable ( quasi ) deformations… I'm wrong ?

Re: Parabolizzazione mirror 300 F 3.8

hello massimar, good heavens, just a beautiful ball !!!
For me, you can safely stop here and suffer with parabolizazzione 2nd round…:ok:

Re: Parabolizzazione mirror 300 F 3.8

The ball is fine. It would obviously be better to have the central defect but for now leave him alone, otherwise you run the risk of starting again from scratch. If you still want to remove it, you have to use a very small patina acting on a limited area. With regard to the action of sub-diameter, as I have always supported, They should be used very carefully because insisting too can generate quite easily zonal errors.

massimar 19-04-14 15:36 Re: Parabolizzazione mirror 300 F 3.8 updating: astrotecnico had said to make two other sub-diameter respectively 20% e al 10%. ( circa ), not knowing how to do, I realized one entrusting, as a good ex-musician, the established technique of improvisation , so do not take inspiration from everything that follows, at least until someone less improviser and more prepared than me or validate these procedures cestinerà. holder / tool used: a beautiful glass mini-ashtray diam. 70 mm ( fuchsia ) paid 1 euro from Marinofamercato . The high sides and the thick glass ( 6 mm ) allow an easy handling at a safe distance from the mirror surface, and it is also indicated as an object of decor , dinners and birthdays with friends. :) Click on the link to enlarge http://s26.postimg.cc/rxrflaujd/small1.jpg He remained so to try this “technological marvel” on the field, So I've done two sessions 10 minutes trying to dig out the center using these past:

Click on the link to enlarge

http://s26.postimg.cc/481zwlw61/stroke3.jpg

after that, for joining the excavated area with the rest of the surface I did a session 30 min with a classical past W for parabolizzazione. (with the sub-diam from 125 mm )

This is the result:

Click on the link to enlarge

http://s26.postimg.cc/juxunpzbt/ron4.jpg

I thought that such a small tool, did not lead to visible results only after extended use, instead it is clearly seen the effect that the center has not yet been connected from the sub-larger diameter.

The question is: I can continue to use this tool ( when you will actually need ) or where to be redone with other methods or materials ?

p.s. Obviously I did this test after it Bart works astrotecnico , They had said that the ball was going well, then digging the center does not do is start to move towards the parable,

Re: Parabolizzazione mirror 300 F 3.8

Write Write …….”…..po-to what we're fuc-sia give an e-u-ro………” Write Write….:D:D

Re: Parabolizzazione mirror 300 F 3.8

The tool is fine: It should not be too formalized its construction. Consider that most of the ones I use are made of wood, then …….
However, the sub-small diameter must be used not getting too close to the center because if you “eat” quickly. Usually you come to a couple of centimeters, not more than. Obviously, if you want to correct the center you have to go to that area, But do not use COC races (relative to the width of the area where you want action) which remove too much material.
Regarding the foma of racing, for sub-diameter used to correct, alternately using a epicloidale is that a zig zag. In any case do not use a tool so small to set the parabolizzazione. Tenderesti create zonal errors. The parabolizzazione must be done with the sub-diameter to 50%. Then touch up areas, to bring them in tolerance, you can do with your ashtray :) If there are errors zonal even smaller amplitude then you can use a 30 millimeters. The area of ​​the adjustment technique is that of pressure to the edge del'utensile. Do not press too much because, I repeat, the sub-diameter material will wear away very quickly and surely you noticed using for just 20 Your minutes 70. It takes nothing to dig pits ! Check often the results by short working sessions. It also regulates the removal of material by acting more or less from the side with the tool. Last thing does not go with the tool overhang too much otherwise cause edge ribattutto.
The parabolizzazione a 3.8 as your require a basic operation and various tweaks. Is’ absolutely normal.

Re: Parabolizzazione mirror 300 F 3.8

Astrotecnico, thank you ! jam packed with content (to study carefully ) , this time with a single action you managed to answer a dozen questions I had whisk head, unbelievable !

Quote:

deabis (write 721641) Write Write …….”…..po-to what we're fuc-sia give an e-u-ro………” Write Write….:D:D

deabis you laugh ? it's beautiful…. :) yes I know, It is all envy for my gem :in:

Re: Parabolizzazione mirror 300 F 3.8

Actually I was taking notes :D:ok:

Re: Parabolizzazione mirror 300 F 3.8

it's true ! :spaf:, that was it “Write Write “, but you know, each artist is sword defends his work, it's this one, well let's face it, without false modesty… It is a work of art !!! :D

Re: Parabolizzazione mirror 300 F 3.8

hello massimar, I would say the exact amount of rosin, cera, trmentina and oil that you used to make the casting and the temperature at which jobs…which it has now been over a year since the utima I did and I do not remember the amount that I used…

Re: Parabolizzazione mirror 300 F 3.8

Although it is still early, interested me too. I work in 15\18 °

Re: Parabolizzazione mirror 300 F 3.8

Ciao Bart, ciao deabis, the “recipe” right to pitch, as you probably know better than I., It is never easy. I can say that the last one I made with which I have the full diameter ( which then is detached ) and the ashtray :) It is good enough:
66% rosins, 33% cera d'fire, three teaspoons of turpentine coffee for a total consists of about 750 gr.
With the mixture so made that I saw under 16-17 degrees of ambient temperature working evil, both for scrolling but especially for the adaptation that becomes very difficult.

the absolute best I've used is the one I have on the sub-diameter 125 mm, but it was just a fluke, because I thought I would use the sub-diameter only as evidence and then I put down in the pot doses eye, and I have no idea of ​​the proportions used, maybe there was a little’ more beeswax and turpentine, but I could not swear..

Re: Parabolizzazione mirror 300 F 3.8

Wow 33% cera d'fire? in what I did yesterday I put it yes and no 10 %…In fact, it seems a bit too hard…:spaf:
I realized that the preparation of the casting is quite a delicate step decisive for the success of the work, and is also the passage that unless you can explain well…In fact even in the various posts he always says to do the test nail or the like and evaluate the penetration…Here the problem !! I never had the chance to do this test on a flow that I know for sure be good so I can not compare to the tests that I do…It would be nice if someone with experience give us the exact recipe to a certain temperature (then % for each ingredient) in such a way as to be able to make a sample, and we can do so the test of’ nail…
It would thus be able to understand many things and you would have a sample “standard” on which we can exchange opinions…

Re: Parabolizzazione mirror 300 F 3.8

Quote:

bart (write 721763) It would be nice if someone with experience give us the exact recipe to a certain temperature …

Bart I'd like it too, but I believe that if nobody has given us this exact formula, most likely because there is no exact formula.
I mean that the factors that may affect the compound are many and it would not be convenient to control them all to achieve the ideal conditions for a specific recipe.

In fact, the aspect that has been more highlighted for the preparation of the pitch ( in addition to the tutorial there are some post depth of Giuliot Also in this topic ) it is precisely on the methods for testing the mettle right.

Astrotecnico on more than one occasion he said that he usually starts with a 10%-15% beeswax and increasing if necessary. This makes me realize three things:

1-the exact formula is not otherwise see because even astrotecnico should have made incremental step and get to the right mixture through checks.

2-the 10% It is probably the minimum threshold below which should not fall.

3-the fact that he spoke not of an upper limit means that the freedom of maneuver is wide to fit precisely to the most diverse conditions.

Then Bart, rassegnamoci, the right formula succeed we will have to invent us , whenever ! :D

Re: Parabolizzazione mirror 300 F 3.8

Then, talking more than doses quantity, with 750 g between wax and rosin comes out from a full tool diameter and it progresses?

Re: Parabolizzazione mirror 300 F 3.8

deabis: The amount is always referred to the diameter you have to play…I for 400 I need 1.5 Kg e.g.…Anyway to get an idea than just re, enough that calculations by volume of the casting (in cm3) and multiply by 1.06 which it is approximately the density of the rosin…you'll get the weight in grams of the total that will help…

Re: Parabolizzazione mirror 300 F 3.8

Indeed with 750 gr. the patina a bit is coming’ “low”, He did not reach the cm thick, one put forward was very little, however sufficient for the limited quantities required by the ashtray.

Re: Parabolizzazione mirror 300 F 3.8

A prescription
And some comments:

Recipe:
A recipe I have it and I step being taken from this book:

Click on the link to enlarge

http://s1.postimg.cc/4y32yt8y3/real…_telescope.jpg

This would be a mixture used by Jean Texereau the laboratory of the Paris Optical, they are used the following ingredients:
– 1kg of already used pitch (that is already loaded abrasive polishing)
– 2kg of rosin (to melt in the previous pitch melted casserole)
– 345 cc of castor oil.
On the tool obtained with this mixture, a 25°C, the imprint of a marble from 8mm, pushed by the weight of 200g 30 seconds, measuring 1.1mm in depth.
To increase the plasticity, It adds another example castor oil carrying to the total volume to 414cc, obtaining a deep imprint 2.1mm (ie a mm longer than before).

Note the quantity is not difficult to derive the proportions to be verified in practice.

Here the wax does not appear, and even turpentine that are still two components responsible for softening.

Comments:
Speaking of optical pitch and of its hardness, that is solved in a different softening temperature, actually it is not easy to find information.
In fact, It come to think that in the pitch being a derivative vegetable, it can be of consistency and quality for variable force with the regions of provenance; seasons and trees around ... and as it is the good wine.

A reference of "hardness" – from that "Thomas" which is in all of us engineers – I think needs to be done by comparison with the imprint left on our pitch based on rosin, in reference to an equal footprint imprinted on a pitch purchased bread, and therefore already graduated at a commercial level for a certain softening temperature (for example Gugolz tabellata here):

Click on the link to enlarge

http://s29.postimg.cc/onxmjk6g3/Pece_Gugolz.jpg

Warning error of exchange of the two print data, for which in the table 55 would melt before soften :eek:)

Today Gugolz, apparently, You can buy in Europe (31 euro to the cylindrical bread from a kg) SOLO googlando "Astronomical Optics Moindrot Sebastien".

The extent of the nail imprint ... for us "modern" is as empirical. But it is often replaced with the more technological the imprint of the ball by ball bearings 8mm, powered by a weight of 200g 30 ..Cioè seconds ... without an engineering "split hairs in four" trespassing in the building of a specific durometer.

Something interesting on the net is derived equally from here:

http://strock.pi.r2.3.14159.free.fr/…/Viscosit.html

And also to the following link:
https://www.salemdist.com/precision/…CH_ACCULAP.pdf

http://archive-org.com/page/661298/2…p / acculap.html

Re: Parabolizzazione mirror 300 F 3.8

Massimar: I completely understand your point of view…I am also convinced that there is no perfect formula that always goes well, but if someone put the amount which used to obtain a good casting for a given temperature, I know that if the rifacessi mettessi me at my home and at the same temperature would get a patina that at least comes close to how it should be a good and would make me account of the texture that has…I refer to your case: if the parties 10-15 % that is suggested, I expect that the final casting can have a little different percentages, but do not differ much from those suggested…I do not I never expected you'd pushed up to 33%, more than double that suggested…