Stai visualizzando 15 post - dal 1 a 15 (di 191 totali)
  • Autore
    Post
  • #4545
    Avatarmaurizio63
    Partecipante
      • Offline

      Hi everyone,Maurice and I have myself started to scratch a mirror 30 cm.
      How often the first experience I have doubts and reading here and in the network someone I think I
      sciolto.Per example now we're scratching with the grain 120, but I think I could work again
      with the 80 I saw that there are still about 6 tenths, I'm planning to go back to 80 until you get to 2 tenths of the arrow
      and then return to 120 but I do not know whether I do well or not.
      Who wants to give me some advice and’ well-accepted.

      maurizio

      #4546
      Massimo MarconiMassimo Marconi
      Moderatore
        • Offline

        hello Maurizio, also welcome in the Forum, Congratulations on your choice to start working a 30 cm, a mirror that will give you great satisfaction in addition to that ( without price ) He did it with your hands ! :good:

        The choice of grit step is never easy, the depth reached is very influenced by the working habits and other factors.
        To better understand and to better analyze the situation, could you tell us that focal depth and then you have to achieve and what kind of past you are using ?

        #4547
        Avatarmaurizio63
        Partecipante
          • Offline

          Ciao
          f / 5 3.75mm arrow past 1/3 center over center

          maurizio

          #4548
          Massimo MarconiMassimo Marconi
          Moderatore
            • Offline

            And the more 6 tenths still to be excavated in theory should be absorbed by the current grain and subsequent. I say in theory because in practice the past 1/3 COC performed without pressure can lead to a very slow deepening, and find yourself in the mirror almost completely frosted end, but with still a long focal.

            Is’ You can go back to 80 and the chordal, but that means redoing the entire surface regularization work ( I do not know where you stand with 120 ) because, how do you know, the chordal with 80 generates a very distant from the sphere surface.

            Without going back to 80. to force the deepening in the middle you can follow two pathways:

            – stretching up to past 1/2 or even 2/3 D COC ( always with the 120 ) and applying pressure to the center.
            You can run some sessions in this mode, with the palm of a hand holding the pressure at the center and the other hand that the mirror guide and verify after some annoyed the depth reached and stop after digging other two-three-tenths.

            – increasing the lateral swiveling out in past 1/3 COC, always with central pressure, always verifying the increase in depth .

            Both techniques can lead to deform the edge , but at this early stage is not a thing worrying because there will be all of the remaining series of abrasives to regularize the surface.

            I prefer the first route, not for some technical reason, but just because I like it here better.

            #4549
            Avatarmaurizio63
            Partecipante
              • Offline

              Thank you,
              but then again a question with 120 what I will have to stand by the arrow? 1tenth ,
              half a tenth ….or arrival at the arrow and then with the abrasive most purposes alternatingly
              mirror / tool?

              maurizio

              #4550
              Massimo MarconiMassimo Marconi
              Moderatore
                • Offline

                Reach precisely the project is a focal “fineness” that is acquired through experience. We must take into account that ,apart from a little’ of luck ( never hurts :-) ) , a certain tolerance on the final depth is physiological.
                After 120 2:00 to 3:00 tenths to be excavated are in accordance, which may prove excessive or too few, It must be assessed along the way and repeated measures, that tasteranno wrist effectiveness of your work.

                As you rightly pointed out, the alternation of the mirror / tool position will allow you to maintain unchanged the arrow, but then again, I would not give too much importance to the accuracy of the depth, three or four cm of focal more or less does not make any difference, I would focus rather on the quality of workmanship that instead can make the difference between a normal mirror and an excellent.

                #4551
                deabisdeabu
                Moderatore
                  • Offline

                  hello Maurizio, bentrovato!
                  If indeed you have not already worked a lot with 120, I counsel you to return to the chordal, possibly with 80. I left the chordal and 80 until 3 mm arrow and I can guarantee that, with the 1/3 COC without variants, It goes down very, very slowly. I think you can safely stop work with chordal a couple of tenths from the final arrow, the limit you can always put a mirror under.
                  :bye:

                  #4552
                  AvatarGiulio TiberinI
                  Moderatore
                    • Offline

                    hello Maurizio. Congratulations on your choice foolhardy to try this interesting gymnastics. Is’ a challenging job but with satisfactions that unfortunately create “addiction” ;-).

                    I would go back to grana 80, because actually 6 tenths away from the arrow are many. You could ascend up to two or three tenths with chordal races, before moving to the unification of the tool and mirror curvatures (to eliminate the disc intact the tool center and the edge intact on the mirror), always with the grain 80.

                    If I'm not wrong, 300F5 on a mirror, every tenth of mm arrow, It changes the focal length of about 5.2mm. So in the process of unification of curves pilot really comfortable with the arrow to center it very well. Because when dimezzerai grain moving from 80 (grain from 2 tenths) to the 120 (grain from 1 tenth) the arrow is very little and move much more slowly than does not move you right now.
                    If you walk the fine abrasives before he unified the two pieces, you'll be hard pressed to unify them and also to the desired focal.

                    #4560
                    Avatarmaurizio63
                    Partecipante
                      • Offline

                      Thank you all for your advice.
                      This weekend will take a decision on how to act.

                      maurizio

                      #4595
                      Avatarmaurizio63
                      Partecipante
                        • Offline

                        Hi guys,
                        I went back to 80 and I came to 1 tenth and a half of the arrow,and I'm always working
                        with 80 to make the spherical mirror. Do you have any advice for me to understand when I reached the ball?

                        #4596
                        Massimo MarconiMassimo Marconi
                        Moderatore
                          • Offline

                          hello Maurizio, I see you progress rapidly, good !
                          With races 1/3 COC regularization of the surface towards the spherical form occurs naturally.
                          Examine the edge of the mirror and try to see if it has the same degree of processing of the center or if it still seems less affected by craters 80.
                          In any case, if you're at that depth should go to 120 80 that better able to uniform the surface.

                          Henceforth the depth measurement will become increasingly more complicated,it is difficult to appreciate differences less than the tenth, should start measuring the focal directly.
                          You can do this by wetting the mirror and measuring it against the sun or following the directions of the article Deabis:

                          Determining the focal work in progress: a useful method in the phases of grinding

                          #4633
                          Avatarmaurizio63
                          Partecipante
                            • Offline

                            I switched to the grain 220 and everything is going well.
                            But I have a lot of carborundum process that I would recover if not’ too complicated,someone recovered? Can you give me some clarification on how to do and whether it makes sense?
                            thank you

                            #4634
                            AvatarGiulio TiberinI
                            Moderatore
                              • Offline

                              hello Maurizio.
                              I guess it is the grit carborundum 80 already used.

                              If so not worth it because it costs more or less 5 EUR per kg + shipment.

                              Out of curiosity I'd say also, its specific gravity 3,2 very close to 2,6 glass, would not allow a separation by decantation. And also, although they can technically use it again without harm to your future slotting a mirror, He would have a poor yield because lose abrasiveness useful to further triturating the already ground glass with which it is polluted.

                              The “makeup” is just a lot of them to really dried, rather than once in a few.
                              It takes just two teaspoons each dried on a mirror Ø300, sprinkled with a little water, if not that you take him away without leaving work.

                              On the practical side, putting more abrasive there is nothing that exponentially increase its share of grain self-destruction that is ground instead of glass.

                              #4660
                              Avatarmaurizio63
                              Partecipante
                                • Offline

                                hello Giulio,
                                thanks for the clarifications (I have many other questions but slowly…) .
                                Reading between the various forums you go from 800 to 1000 I who have the 800
                                I should switch from 600 to the 1000 It could go well?

                                #4661
                                AvatarGiulio TiberinI
                                Moderatore
                                  • Offline

                                  You do not worry it's fine!

                                  Switch from 600 to the 1000 In practice it has to follow the philosophy of the normal progressive halving the diameter of the abrasive grain. In fact, the grain 600 It has an average diameter of the abrasive grain of 16 microns; while 1000 it has to 9 microns….so almost half.

                                  By placing the grain 800 proseguiresti with an intermediate step between the 600 and 1000, that owning 800 it would be a shame not to take advantage, but not having you just have to work a little longer with 1000 to enable it to eliminate the craters left by 600, which they are slightly larger than those that would leave the 800, and nothing more.

                                  Calculates that I have never used the 1000, but I am passed to polishing with cerium oxide and pitch, after 800. And in this case it's me that I then had to work harder with pitch to polish the craters of my 800, while you'd be in polishing “plug” small craters left from the grain 1000.

                                  The problem that arises in practice is that the work to see if the craters of the previous grain disappeared both the center and the edge of the mirror (because, alas, they do not go at the same speed) It is very useful as a microscope 100 magnifications that costs less than 20 euro, but it allows you to appreciate craters otherwise invisible even with eye turned to the contrary.
                                  that microscope (I've always used) if you care to find him Googling “Microscope 100x laptop with LED lighting (2 * aa)”.

                                Stai visualizzando 15 post - dal 1 a 15 (di 191 totali)
                                • Devi essere connesso per rispondere a questo topic.