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Re: [atm_free] Re: Soft Pitch

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  • Asad Scientist
    I ve spent at least 10 hours on polishing. The surface still shows a very dim reflection in Laser Test. Before test, I ensure that the mirror is clean from
    Message 1 of 27 , Jan 1, 2012
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      I've spent at least 10 hours on polishing. The surface still shows a very dim reflection in Laser Test. Before test, I ensure that the mirror is clean from dust or any other impurity. The polishing agent(CeO) solution is thick enough. I think that it is due to thick CeO solution that the mirror is not completely polishing. All the mirror has the same DIM reflection except outer 0.25" edge radius. Kindly guide me in this matter. How thin / thick should be the solution of Cerium Oxide so that it may polish in a fine way. The pits are too small to observe under a high power magnifier, however, Laser test has shown that the I need to do more work on polishing. The pitch lap is free from dust particles / impurity. Mirror has also been washed by soap. So, if there is anything left that play role in polishing, that is CeO solution. I am not sure about any dust particles or impurity in that polishing agent solution.


      Asad
    • Mark Whitaker
      You described the solution similar to skim milk in one of your earlier posts.  This should be about right.  Some folks prefer it even thinner for a
      Message 2 of 27 , Jan 1, 2012
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        You described the solution similar to "skim milk" in one of your earlier posts.  This should be about right.  Some folks prefer it even thinner for a smoother surface.

        If you only have 10 hours on an 8" mirror, then I wouldn't be concerned.  In fact, I would encourage you do to another 5 hours minimum.

        Mark


        From: Asad Scientist <asadscientist@...>
        To: atm_free@yahoogroups.com
        Sent: Sunday, January 1, 2012 11:00 AM
        Subject: Re: [atm_free] Re: Soft Pitch

         
        I've spent at least 10 hours on polishing. The surface still shows a very dim reflection in Laser Test. Before test, I ensure that the mirror is clean from dust or any other impurity. The polishing agent(CeO) solution is thick enough. I think that it is due to thick CeO solution that the mirror is not completely polishing. All the mirror has the same DIM reflection except outer 0.25" edge radius. Kindly guide me in this matter. How thin / thick should be the solution of Cerium Oxide so that it may polish in a fine way. The pits are too small to observe under a high power magnifier, however, Laser test has shown that the I need to do more work on polishing. The pitch lap is free from dust particles / impurity. Mirror has also been washed by soap. So, if there is anything left that play role in polishing, that is CeO solution. I am not sure about any dust particles or impurity in that polishing agent solution.


        Asad


      • Mark Christensen
        Asad, The mirror is plate glass, correct? 10 hours of work seems like a lot of time for it not be be completed when polishing with CeO. In 10 hours a Pyrex
        Message 3 of 27 , Jan 2, 2012
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          Asad,
           
          The mirror is plate glass, correct?
           
          10 hours of work seems like a lot of time for it not
          be be completed when polishing with CeO.
           
          In 10 hours a Pyrex mirror would polish out, in my
          experience.
           
          Perhaps the lap problem you described and fixed earlier
          made the (alas, many) hours of work ineffective.
           
          If it doesn't (as Mark W suggests) polish out in five
          more hours with your new lap I think there may have
          been problem with completing the fine grinding, as
          painful as that is to contemplate.
           
          Mark Christensen
        • Asad Scientist
          If you think that fine grinding is not finished properly, then should I move back to fine grinding?
          Message 4 of 27 , Jan 2, 2012
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            If you think that fine grinding is not finished properly, then should I move back to fine grinding?
          • Mark Whitaker
            You are the only person who can make that call since only you can see the surface.  I personally don t like the laser test as a definitive test. Use a 10x
            Message 5 of 27 , Jan 2, 2012
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              You are the only person who can make that call since only you can see the surface.  I personally don't like the laser test as a definitive test.

              Use a 10x magnifier and make some Sharpie ink dots on the surface of the mirror.  Do this for a representative area of the mirror.  Use the ink dots on the surface to help focus the magnifier.  Try to get an oblique reflection near the dot and look at the illuminated surface for pits.  Or look at the surface near the dots while illuminating from the back.  If you see only a few small, scattered pits, then you are probably done.  If you see a veil of pits, than keep on polishing.

              The time it takes to get a complete polish can be greatly affected by the effort spent smoothing and the quality of the final grades of abrasive used.  I have never given any of my mirrors less than 15 hours and I usually give the 20 to 24 hours.  But I use a machine so its easy for me to do that.  If you polish long enough and still can't seem to reduce the pits to a satisfactory level, then you have a tough decision to make.  A small number of pits, even a veil of small pits, will not significantly effect normal observing, so it becomes a personal decision of what you are willing to accept.  There is always the "next" mirror.

              Mark





              From: Asad Scientist <asadscientist@...>
              To: atm_free@yahoogroups.com
              Sent: Monday, January 2, 2012 11:47 AM
              Subject: Re: [atm_free] Re: Soft Pitch

               
              If you think that fine grinding is not finished properly, then should I move back to fine grinding?


            • Jerry
              Hello Asad, I prefer a LED flashlight for inspecting the polish. I poke a 3 mm hole in aluminum foil and tape it to the front of the flashlight. This gives
              Message 6 of 27 , Jan 2, 2012
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                Hello Asad,

                 

                I prefer a LED flashlight for inspecting the polish.  I poke a 3 mm hole in aluminum foil and tape it to the front of the flashlight.  This gives me a sufficiently small and bright beam.  

                 

                When you shine the light on the mirror surface,  it is almost certain you will see some scatter reflection even from a fully polished surface.   It is extremely difficult (impossible?) to clean the glass of all traces of chemical films and dust. 

                Areas that are slow to polish will usually show as zones (all the way around the mirror at some distance or distances from the mirror’s center).  And it is the nature of the process that the polishing action will probably be fastest at the mirror’s center and slowest at the edge.  As you sweep the flashlight beam slowly radially from the center to the edge you look for is differences in the amount of reflected light from the mirror’s surface.  The difference is film and dust only, or film and dust plus poor polish.  When you can see no difference in reflection intensity as you sweep along radials from center to edge, polish is complete.

                 

                I think what you have described so far is all within what I would consider to be normal progress.  The edge is last to polish… polish until the edge looks as clear as all the other zones.

                Here is how I speed up polish for edge.

                http://ww4rf.net/atm/  

                The video shows a 4” being worked,  but the concept works well for 8” mirrors too.

                10 hours is not so much time for polishing.   An 8” could be polished in that time,  but inefficiencies caused by the hard pitch, and maybe some other things,  might make 20 or more hours more reasonable.

                Keep on stroking.

                If you work TOT remember to take precautions against work-stand flexure induced astigmatism.

                Jerry

                 

                From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of Asad Scientist
                Sent: Sunday, January 01, 2012 12:01 PM
                To: atm_free@yahoogroups.com
                Subject: Re: [atm_free] Re: Soft Pitch

                 



                I've spent at least 10 hours on polishing. The surface still shows a very dim reflection in Laser Test. Before test, I ensure that the mirror is clean from dust or any other impurity. The polishing agent(CeO) solution is thick enough. I think that it is due to thick CeO solution that the mirror is not completely polishing. All the mirror has the same DIM reflection except outer 0.25" edge radius. Kindly guide me in this matter. How thin / thick should be the solution of Cerium Oxide so that it may polish in a fine way. The pits are too small to observe under a high power magnifier, however, Laser test has shown that the I need to do more work on polishing. The pitch lap is free from dust particles / impurity. Mirror has also been washed by soap. So, if there is anything left that play role in polishing, that is CeO solution. I am not sure about any dust particles or impurity in that polishing agent solution.

                 

                 

                Asad




              • Asad Scientist
                Hi everyone, Mirror s surface is same from centre to edges. Total hours spent on polishing are 16 hours. Now I m able to say that mirror has been polished.
                Message 7 of 27 , Jan 3, 2012
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                  Hi everyone,

                  Mirror's surface is same from centre to edges. Total hours spent on polishing are 16 hours. Now I'm able to say that mirror has been polished. I've tested is using LED test.

                  The existing figure of the mirror Inside the ROC is given is this video I've just uploaded :




                  Kindly watch it. I think mirror's portion has long focal length than the outer portion. And there is a small depression just in the centre of mirror too.
                • Jerry
                  Hello Asad, How does the pitch lap look now? Can you send a picture? From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of Asad
                  Message 8 of 27 , Jan 3, 2012
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                    Hello Asad,

                     

                    How does the pitch lap look now?  Can you send a picture?

                     

                    From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of Asad Scientist
                    Sent: Tuesday, January 03, 2012 6:41 AM
                    To: atm_free@yahoogroups.com
                    Subject: Re: [atm_free] Re: Soft Pitch

                     



                    Hi everyone,

                     

                    Mirror's surface is same from centre to edges. Total hours spent on polishing are 16 hours. Now I'm able to say that mirror has been polished. I've tested is using LED test.

                     

                    The existing figure of the mirror Inside the ROC is given is this video I've just uploaded :

                     

                     

                     

                     

                    Kindly watch it. I think mirror's portion has long focal length than the outer portion. And there is a small depression just in the centre of mirror too.




                  • Mark Whitaker
                    If the KE is coming in from the right then it looks like you have an oblate spheroid with the outer zone rolled sharply down and possibly extreme edge turned
                    Message 9 of 27 , Jan 3, 2012
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                      If the KE is coming in from the right then it looks like you have an oblate spheroid with the outer zone rolled sharply down and possibly extreme edge turned down.
                      If you are happy with the polish, it is time to start figuring.  You need a tester that can accurately measure the shadows longitudinally and you'll need to prepare a Couder mask.  Download a copy of FigureXP if you don't already have it.  You can get the link to the software and plans for a serviceable tester from Stellafane.org.

                      In the meantime, you need to do more polishing.  It appears that the shadows break strongly in the outer zone.  At this point, I would worry less about the slight artifact in the center or the oblate spheroid and focus on the outer zone and the edge.  To start, do another hour, TOT, using a "w" stroke and a full size lap.  Make sure you have good lap contact and the overhang should be about 1.3" at the ends of the stroke and the "w" should be constrained to about .7" at the sides of the stroke.  Working TOT mainly wears the outer zones of the mirror.

                      Mark


                      From: Asad Scientist <asadscientist@...>
                      To: atm_free@yahoogroups.com
                      Sent: Tuesday, January 3, 2012 5:40 AM
                      Subject: Re: [atm_free] Re: Soft Pitch

                       
                      Hi everyone,

                      Mirror's surface is same from centre to edges. Total hours spent on polishing are 16 hours. Now I'm able to say that mirror has been polished. I've tested is using LED test.

                      The existing figure of the mirror Inside the ROC is given is this video I've just uploaded :




                      Kindly watch it. I think mirror's portion has long focal length than the outer portion. And there is a small depression just in the centre of mirror too.


                    • Asad Scientist
                      The picture of pitch lap is attached. And the K E is from right side.
                      Message 10 of 27 , Jan 3, 2012
                      The picture of pitch lap is attached. And the K E is from right side.
                    • Jerry
                      Hello Asad, The mirror’s profile would look something like that shown in the attachment. Oblate with a turn down edge. The shadows with the present knife
                      Message 11 of 27 , Jan 4, 2012
                      • 1 Attachment
                      • 59 KB

                      Hello Asad,

                       

                      The mirror’s profile would look something like that shown in the attachment.  Oblate with a turn down edge.

                      The shadows with the present knife position shadows show the central area inside the raised outer zone as a hill,  but the knife could be moved farther from the mirror to show that area flat.  Next time you test, adjust the knife to show that area flat.  There are some shallow ring zones in there,  but otherwise it is flat.   Or you could Ronchi test to see if I am right about that.  

                      The central hole is not deep and could be removed quickly,  or even ignored because it will be hidden by the secondary.  But don’t worry about this now.  It will probably disappear without effort.

                      The turn down edge is about ½ inch wide.  The width of the TDE makes me think the diameter of your lap is 7”.   I see that you have not beveled the lap.  That is good,   but is the lap the same diameter as the mirror?   

                       

                      The TOT fast edge polish stroke shown in the video link is also useful for removing the high outer zone and turn down edge.

                      http://ww4rf.net/atm/  

                      There is a MOT method that works much the same.   The mirror is offset  ~ 15 to 25 mm to the left and applying pressure with the right hand on the right side mirror and stroking with a straight stroke of about ¼ or 1/3 D in length.

                       

                      I prefer using mostly TOT to fix the outer zone and edge.

                       

                      I usually use a mix different size W’s MOT and TOT with the fast edge polish stroke shown in the video.  I will do 1 or 2 trips around the mirror with one stroke and then switch to a different size. And I will work MOT and TOT.

                       

                      A work session might be something like this:

                       

                      2 times around TOT edge stroke (as shown in the video).

                      1 time around  TOT medium W.

                      1 time around  TOT small  W.

                      1 time around  TOT large W.

                       

                      1 time around  MOT medium W.

                      1 time around  MOT small  W.

                       

                      1 time around TOT COC 1/3 D

                      1 time around  TOT large W.

                       

                      Small W is about  ¼ D to 1/3 D.

                      Medium W is about 1/2D.

                      Large W is about 2/3 to ¾ D.

                       

                      Depending on how long you want to work,  you might do this sequence one or more times.   For this first session 45 minutes to 1 hour of work will be ok.

                       

                      For me each step is about 25 or 30 degrees as work my way around the barrel.  That makes about 12 to 14 steps for a full turn around the mirror (TOT).  In your grinding video you turn the board with bottom disk about 70 or 80 degrees at a time.  If you use the same procedure working with the lap,  it will take you about 3 full rotations to do what I do in 1 trip around the barrel.

                       

                      Here is a link to a video showing a TOT “Big W stroke” TOT.

                      http://www.youtube.com/watch?v=IVUuUWbyyFs&feature=mfu_in_order&list=UL

                       

                      It would be good if you posted a YouTube video of your polishing methods.

                       

                      Alternating TOT and MOT with various strokes will probably smooth the curve very well as it removes the high outer zone and TDE. 

                       

                      You should be in familiar territory now.  This is much the same shape you had when you started figuring your 6” f:11.   You can use what you learned on that one and learn some new stuff too.  Learn as many lessons as you can while you do a better job on this one.  the more you learn on this one the easier the 14” will be when you make that one.

                       

                      Jerry

                       

                      From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of Asad Scientist
                      Sent: Wednesday, January 04, 2012 1:07 AM
                      To: atm_free@yahoogroups.com
                      Subject: Re: [atm_free] Re: Soft Pitch [2 Attachments]

                       

                      [Attachment(s) from Asad Scientist included below]

                      The picture of pitch lap is attached. And the K E is from right side.

                      Attachment(s) from Asad Scientist

                      2 of 2 Photo(s)

                    • Mark Whitaker
                      Yes, if you are using a smaller lap, you are going to have problems.  Assuming a full size lap, the outer zone looks more like a raised ring.  This can be
                      Message 12 of 27 , Jan 4, 2012
                      • 0 Attachment
                        Yes, if you are using a smaller lap, you are going to have problems.  Assuming a full size lap, the outer zone looks more like a raised ring.  This can be caused by a glazed facet.  It is not a bad idea to occasionally brush the lap with a brass or stainless steel wire brush.  Don't use a common steel bristle brush as you don't want to contaminate the lap with rust particles.  But your lap looks fairly uniform.

                        Working TOT does work preferentially wear the outer zones increasing their radius.  That will bring the mirror more in line with the longer radius of the inner portion.

                        You just need to get the mirror corrected to a uniform figure of revolution with no zones and overall correction less than the desired parabola.  A clean oblate or prolate ellipsoid can be parabolized from the outset.  However, I encourage less experienced mirror makers to produce a sphere mainly as a confidence builder.  Once you get to the point where a clean sphere with little effort, you are well on your way to producing quality aspheres.

                        Mark


                        From: Jerry <wa4guu@...>
                        To: atm_free@yahoogroups.com
                        Sent: Wednesday, January 4, 2012 9:18 AM
                        Subject: [atm_free] Re: Soft Pitch [1 Attachment]

                         
                        Hello Asad,
                         
                        The mirror’s profile would look something like that shown in the attachment.  Oblate with a turn down edge.
                        The shadows with the present knife position shadows show the central area inside the raised outer zone as a hill,  but the knife could be moved farther from the mirror to show that area flat.  Next time you test, adjust the knife to show that area flat.  There are some shallow ring zones in there,  but otherwise it is flat.   Or you could Ronchi test to see if I am right about that.  
                        The central hole is not deep and could be removed quickly,  or even ignored because it will be hidden by the secondary.  But don’t worry about this now.  It will probably disappear without effort.
                        The turn down edge is about ½ inch wide.  The width of the TDE makes me think the diameter of your lap is 7”.   I see that you have not beveled the lap.  That is good,   but is the lap the same diameter as the mirror?   
                         
                        The TOT fast edge polish stroke shown in the video link is also useful for removing the high outer zone and turn down edge.
                        http://ww4rf.net/atm/  
                        There is a MOT method that works much the same.   The mirror is offset  ~ 15 to 25 mm to the left and applying pressure with the right hand on the right side mirror and stroking with a straight stroke of about ¼ or 1/3 D in length.
                         
                        I prefer using mostly TOT to fix the outer zone and edge.
                         
                        I usually use a mix different size W’s MOT and TOT with the fast edge polish stroke shown in the video.  I will do 1 or 2 trips around the mirror with one stroke and then switch to a different size. And I will work MOT and TOT.
                         
                        A work session might be something like this:
                         
                        2 times around TOT edge stroke (as shown in the video).
                        1 time around  TOT medium W.
                        1 time around  TOT small  W.
                        1 time around  TOT large W.
                         
                        1 time around  MOT medium W.
                        1 time around  MOT small  W.
                         
                        1 time around TOT COC 1/3 D
                        1 time around  TOT large W.
                         
                        Small W is about  ¼ D to 1/3 D.
                        Medium W is about 1/2D.
                        Large W is about 2/3 to ¾ D.
                         
                        Depending on how long you want to work,  you might do this sequence one or more times.   For this first session 45 minutes to 1 hour of work will be ok.
                         
                        For me each step is about 25 or 30 degrees as work my way around the barrel.  That makes about 12 to 14 steps for a full turn around the mirror (TOT).  In your grinding video you turn the board with bottom disk about 70 or 80 degrees at a time.  If you use the same procedure working with the lap,  it will take you about 3 full rotations to do what I do in 1 trip around the barrel.
                         
                        Here is a link to a video showing a TOT “Big W stroke” TOT.
                        http://www.youtube.com/watch?v=IVUuUWbyyFs&feature=mfu_in_order&list=UL
                         
                        It would be good if you posted a YouTube video of your polishing methods.
                         
                        Alternating TOT and MOT with various strokes will probably smooth the curve very well as it removes the high outer zone and TDE. 
                         
                        You should be in familiar territory now.  This is much the same shape you had when you started figuring your 6” f:11.   You can use what you learned on that one and learn some new stuff too.  Learn as many lessons as you can while you do a better job on this one.  the more you learn on this one the easier the 14” will be when you make that one.
                         
                        Jerry
                         
                        From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of Asad Scientist
                        Sent: Wednesday, January 04, 2012 1:07 AM
                        To: atm_free@yahoogroups.com
                        Subject: Re: [atm_free] Re: Soft Pitch [2 Attachments]
                         
                        [Attachment(s) from Asad Scientist included below]

                        The picture of pitch lap is attached. And the K E is from right side.
                        Attachment(s) from Asad Scientist
                        2 of 2 Photo(s)


                      • Ali Khan
                        Is there a better way to put pitch hardness in numbers? Suppose we have a 10mm dia steel rod of say 100g mass. How deep an indent is expected in say one hour?
                        Message 13 of 27 , Jan 4, 2012
                        • 0 Attachment
                          Is there a better way to put pitch hardness in numbers? Suppose we have a 10mm dia steel rod of say 100g mass. How deep an indent is expected in say one hour? That sort of thing.

                          --- In atm_free@yahoogroups.com, Mark Whitaker <tnut55@...> wrote:
                          >
                          > Yes, if you are using a smaller lap, you are going to have problems.  Assuming a full size lap, the outer zone looks more like a raised ring.  This can be caused by a glazed facet.  It is not a bad idea to occasionally brush the lap with a brass or stainless steel wire brush.  Don't use a common steel bristle brush as you don't want to contaminate the lap with rust particles.  But your lap looks fairly uniform.
                          >
                          > Working TOT does work preferentially wear the outer zones increasing their radius.  That will bring the mirror more in line with the longer radius of the inner portion.
                          >
                          > You just need to get the mirror corrected to a uniform figure of revolution with no zones and overall correction less than the desired parabola.  A clean oblate or prolate ellipsoid can be parabolized from the outset.  However, I encourage less experienced mirror makers to produce a sphere mainly as a confidence builder.  Once you get to the point where a clean sphere with little effort, you are well on your way to producing quality aspheres.
                          >
                          > Mark
                          >
                          >
                          >
                          > ________________________________
                          > From: Jerry <wa4guu@...>
                          > To: atm_free@yahoogroups.com
                          > Sent: Wednesday, January 4, 2012 9:18 AM
                          > Subject: [atm_free] Re: Soft Pitch [1 Attachment]
                          >
                          >
                          >  
                          > [Attachment(s) from Jerry included below]
                          > Hello Asad,
                          >  
                          > The mirror’s profile would look something like that shown in the attachment.  Oblate with a turn down edge.
                          > The shadows with the present knife position shadows show the central area inside the raised outer zone as a hill,  but the knife could be moved farther from the mirror to show that area flat.  Next time you test, adjust the knife to show that area flat.  There are some shallow ring zones in there,  but otherwise it is flat.   Or you could Ronchi test to see if I am right about that.  
                          > The central hole is not deep and could be removed quickly,  or even ignored because it will be hidden by the secondary.  But don’t worry about this now.  It will probably disappear without effort.
                          > The turn down edge is about ½ inch wide.  The width of the TDE makes me think the diameter of your lap is 7”.   I see that you have not beveled the lap.  That is good,   but is the lap the same diameter as the mirror?   
                          >  
                          > The TOT fast edge polish stroke shown in the video link is also useful for removing the high outer zone and turn down edge.
                          > http://ww4rf.net/atm/  
                          > There is a MOT method that works much the same.   The mirror is offset  ~ 15 to 25 mm to the left and applying pressure with the right hand on the right side mirror and stroking with a straight stroke of about ¼ or 1/3 D in length.
                          >  
                          > I prefer using mostly TOT to fix the outer zone and edge.
                          >  
                          > I usually use a mix different size W’s MOT and TOT with the fast edge polish stroke shown in the video.  I will do 1 or 2 trips around the mirror with one stroke and then switch to a different size. And I will work MOT and TOT.
                          >  
                          > A work session might be something like this:
                          >  
                          > 2 times around TOT edge stroke (as shown in the video).
                          > 1 time around  TOT medium W.
                          > 1 time around  TOT small  W.
                          > 1 time around  TOT large W.
                          >  
                          > 1 time around  MOT medium W.
                          > 1 time around  MOT small  W.
                          >  
                          > 1 time around TOT COC 1/3 D
                          > 1 time around  TOT large W.
                          >  
                          > Small W is about  ¼ D to 1/3 D.
                          > Medium W is about 1/2D.
                          > Large W is about 2/3 to ¾ D.
                          >  
                          > Depending on how long you want to work,  you might do this sequence one or more times.   For this first session 45 minutes to 1 hour of work will be ok.
                          >  
                          > For me each step is about 25 or 30 degrees as work my way around the barrel.  That makes about 12 to 14 steps for a full turn around the mirror (TOT).  In your grinding video you turn the board with bottom disk about 70 or 80 degrees at a time.  If you use the same procedure working with the lap,  it will take you about 3 full rotations to do what I do in 1 trip around the barrel.
                          >  
                          > Here is a link to a video showing a TOT “Big W stroke” TOT.
                          > http://www.youtube.com/watch?v=IVUuUWbyyFs&feature=mfu_in_order&list=UL
                          >  
                          > It would be good if you posted a YouTube video of your polishing methods.
                          >  
                          > Alternating TOT and MOT with various strokes will probably smooth the curve very well as it removes the high outer zone and TDE. 
                          >  
                          > You should be in familiar territory now.  This is much the same shape you had when you started figuring your 6” f:11.   You can use what you learned on that one and learn some new stuff too.  Learn as many lessons as you can while you do a better job on this one.  the more you learn on this one the easier the 14” will be when you make that one.
                          >  
                          > Jerry
                          >  
                          > From:atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of Asad Scientist
                          > Sent: Wednesday, January 04, 2012 1:07 AM
                          > To: atm_free@yahoogroups.com
                          > Subject: Re: [atm_free] Re: Soft Pitch [2 Attachments]
                          >  
                          > [Attachment(s) from Asad Scientist included below]
                          >
                          > The picture of pitch lap is attached. And the K E is from right side.
                          > Attachment(s) from Asad Scientist
                          > 2 of 2 Photo(s)
                          > DSCN0270.jpg
                          > DSCN0271.jpg
                          >
                        • Jerry
                          Hello Ali, I think the most common pitch tester design used by amateurs would be as described appendix J of the 2nd edition of How to Make a Telescope by
                          Message 14 of 27 , Jan 5, 2012
                          • 0 Attachment
                            Hello Ali,

                            I think the most common pitch tester design used by amateurs would be as described appendix J of the 2nd edition of "How to Make a Telescope" by Jean Texereau.
                            This design uses a 1 kg weight to press a rod into the pitch. The tip of the rod is tapered 14 degrees and the point is flattened to 1 mm diameter.
                            Penetration of the rod into the pitch is measured after 5 minutes.
                            The range of desirable penetration rates is described in the appendix as:
                            Penetration of less than 0.02" indicates pitch is too hard.
                            Penetration of more than 0.24" indicates pitch is too soft.
                            Penetration of 0.07" is the sweet spot.

                            A tester is shown here. Scroll down about 3/4 of the page.
                            http://stellafane.org/tm/atm/polish/lap-stuff.html

                            I like the mechanical features of this one.
                            http://www.turbofast.com.au/astrotel/pitchtester.html

                            This tester uses a 6mm ball for the penetrator and 500 gram weight.
                            http://www.zygo.com/library/papers/proc_3782_72.pdf


                            Jerry




                            > -----Original Message-----
                            > From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com]
                            > On Behalf Of Ali Khan
                            > Sent: Thursday, January 05, 2012 1:27 AM
                            > To: atm_free@yahoogroups.com
                            > Subject: [atm_free] Re: Soft Pitch
                            >
                            > Is there a better way to put pitch hardness in numbers? Suppose we have a
                            > 10mm dia steel rod of say 100g mass. How deep an indent is expected in say
                            > one hour? That sort of thing.
                          • Asad Scientist
                            Jerry, Thank you very much for explanation.The Pitch Lap has 8.25 diameter and the mirror has 8.5 diameter. So I don t think this an adequate difference that
                            Message 15 of 27 , Jan 5, 2012
                            • 0 Attachment
                              Jerry, Thank you very much for explanation.The Pitch Lap has 8.25" diameter and the mirror has 8.5" diameter. So I don't think this an adequate difference that can cause mirror troubles. 

                              I have something to ask:

                              How much left and right should I move the mirror (during MOT) or Pitch lap (during TOT) while using small, medium and large 'W' strokes? 



                              Asad
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