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Curt is the worst mirror maker ever!

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#101 Pinbout

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Posted 22 February 2018 - 11:38 PM

that's good enough



#102 charlievictor102

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Posted 22 February 2018 - 11:39 PM

Thanks Danny.  Pouring the pitch now.

 

Curt



#103 Pinbout

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Posted 22 February 2018 - 11:49 PM

I can smell it from here



#104 dave brock

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Posted 23 February 2018 - 07:20 PM

I'm a bit late to this thread but for the benefit of any new mirror makers looking:-

 

Regarding the Ronchi images in posts #16 and #44

Some of my apparent TDE in the Ronchi diagram is because I have multiple Ronchi lines in front of the light source. The superimposed, multiple images make it appear to bend at the upper right.  Is that correct?

 

 

The Ronchi diffraction at the edge causes overlapping images but with a good edge you should see that the lines do not bend in any of the overlapping images. The lines run off the edge of the inside image cleanly and then there is a sideways shift of the lines in the middle of the overlapping images but they still run off clean in a more or less vertical direction. With a TDE the lines bend before the edge of the inside image and continue in a sideways direction in the middle image.

First two with no TDE, third with TDE.

 

IMG_1914.jpg

IMG_1912 half.jpg

sml_gallery_284567_8868_18400.jpg

 

 

Dave

 


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#105 charlievictor102

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Posted 26 February 2018 - 12:18 PM

So I made the new (thicker) full-size tool.  I did an hour spin polishing with 15% overhang.  Got the ring defects as expected.  Did about an hour by hand of COC, 1/3 strokes, alternate TOT (10 lbs), MOT (no weight), pedestal at about 3 RPM, and warm&cold presses with the same weight as polishing.

 

This is the 12.4 inch, f/5, about 0.4 inches beyond ROC:

201802125 2a

 

This is about 0.4 inside of ROC:

201802125 2b

 

I'm liking the smoothness.  I didn't seem to roll the edge like I did before.

 

But I don't like the TDE.  I'm going back to the 15% overhang spin polishing which really helped the TDE before.  I will keep you posted.

 

Curt



#106 Pinbout

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Posted 26 February 2018 - 12:35 PM

And your still oblate



#107 Astro Daddy

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Posted 27 February 2018 - 06:56 AM

And your still oblate

Just trying to learn how to interpret the Ronchi grams. The reason you are saying it is still oblate is because there is a slight curving of the lines towards the center of the mirror? And the turned down edge is because the end of the lines also turn towards the center of the mirror?
John

#108 Pinbout

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Posted 27 February 2018 - 01:11 PM

 

And your still oblate

Just trying to learn how to interpret the Ronchi grams. The reason you are saying it is still oblate is because there is a slight curving of the lines towards the center of the mirror? And the turned down edge is because the end of the lines also turn towards the center of the mirror?
John

 

one important description your missing on your observations is, "outside RoC" otherwise everything you describe is correct.

 

and he should always post inside RoC 1st...confusing to have outside first.



#109 charlievictor102

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Posted 27 February 2018 - 11:37 PM

I went back to machine spin polishing the center.  Then a bunch of COC, 1/3 strokes by hand.

 

This is the 12.4 inch, f/5, 85 LPI, about 0.4 inches inside ROC:

201802127 3a

 

This is about 0.4 outside of ROC:

201802127 3b

 

Raw Foucault very close to ROC.

201802127 3d

 

Very close to ROC with 20 second video filter:

201802127 3c

 

 

About the same as before.  This is about as good as I can do.

 

Curt


Edited by charlievictor102, 27 February 2018 - 11:38 PM.


#110 Dale Eason

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Posted 28 February 2018 - 12:27 AM

That is looking pretty nice.  The next step an experienced person would do would be to take the ronchi closer to ROC on each side so that it shows only about 3 lines.  That is far more sensitive and allows one a better analysis.

 

Dale


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#111 hamishbarker

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Posted 28 February 2018 - 05:39 AM

Couldnt be worse than

 

med_gallery_106859_4364_1407449854_26407

I feel dizzy...



#112 Pinbout

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Posted 28 February 2018 - 07:03 AM

 

Couldnt be worse than

 

med_gallery_106859_4364_1407449854_26407

I feel dizzy...

 

really? that's what you got to shoot your shot? fingertap.gif

 

lol.gif



#113 Pinbout

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Posted 28 February 2018 - 07:05 AM

That is looking pretty nice.  The next step an experienced person would do would be to take the ronchi closer to ROC on each side so that it shows only about 3 lines.  That is far more sensitive and allows one a better analysis.

 

Dale

at this point  5 lines is fine especially for...f5?

more important is to keep using the same amount of lines which you seem to  do well.

 

when you get really really close you can switch to using 2 or 3 lines

 

at least your not oblate and going in the right direction.

 

keep parabolizing


Edited by Pinbout, 28 February 2018 - 07:10 AM.


#114 Pinbout

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Posted 28 February 2018 - 08:51 AM

look even with 5 lines can see the hole that your developing...you need it to parabolize so I wouldn't worry about it.

 

you need to make it deeper and push it out to the edge.

 

and the edge, I wouldn't worry about that either till you get a better shaped negative conic

 

point being 5 lines is plenty sensitive enough for doing what your doing now.

 

hole.JPG



#115 charlievictor102

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Posted 28 February 2018 - 03:21 PM

Just so you know, there was a lot of activity between my Post #106 and Post #109.  I dug out the middle and tried to push it out to the edge.

 

All Ronchi 85LPI, 12.4 inch mirror, f/5, inside ROC about 0.4 inches.

 

This is repeat of Post #106 when I diverted to work on the TDE:

201802125 2b

 

After spin polishing with fixed post and 15% overhang:

201802126 2b

 

Some more polishing with the new eccentric added to the post:

201802126 3b

 

Now with a lot of by hand COC:

201802126 4b

 

Then a repeat of my Post #109:

201802127 3a

 

Curt



#116 Pinbout

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Posted 28 February 2018 - 04:23 PM

all you had to do is blend in the kink

 

should of stayed.JPG


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#117 Mark Harry

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Posted 28 February 2018 - 05:05 PM

Yeah, well he's following your suggestions, huh? The edge wasn't really fixed correctly. Curt did pretty well. But you suggested that was GOOD ENOUGH. 
It wasn't in retrospect. You should have suggested backtracking a bit.
All I'm gonna say.
M.



#118 Pinbout

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Posted 28 February 2018 - 05:48 PM

No he’s not following my suggestions

 

so If your implying I’m leading him down the wrong path, you are showing you can’t even follow the thread.

 

his edge is about a 1/4~ turned. He can fix it after he gets past a sphere, no big deal.

 

why fix it while your still oblate? It will turn again going thru a sphere to a neg. conic.


Edited by Pinbout, 28 February 2018 - 05:54 PM.


#119 MKV

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Posted 28 February 2018 - 09:27 PM

I don't know, the whole thing is going around in circles (no pun intended). The mirror looked pretty good in #109 except for the turned edge. Fixing the edge (short strokes TOT) will make it slightly oblate, and from there it can be parabolized. He should use his hands, subdiameter tool and elliptical blending strokes barely reaching the edge -- and work with hands rather than spin polishing, imo.


Edited by MKV, 01 March 2018 - 01:21 AM.


#120 Pinbout

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Posted 28 February 2018 - 09:31 PM

I never fix an edge if I’m oblate

 

i always make sure the mirror is a sphere or elliptical 

 

It’s so easy to turn the edge going from oblate to another conic



#121 charlievictor102

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Posted 28 February 2018 - 10:32 PM

Danny is correct.  I have not been following his recommendations.  He has been encouraging me to abandon the TDE and start to parabolize.  Virtually everything I have read has said that this is a bad idea.  The 2 or 3 times I've come close to a decent figure and then tried to correct the TDE have not been very successful.  I have been, in fact, "backtracking" to correct the TDE.  I posted #115 because I got the impression that Danny thought I went from post #106 to #109 with a little polishing.  I did not intend to cause a flame war.

 

Curt


Edited by charlievictor102, 28 February 2018 - 10:35 PM.


#122 Mark Harry

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Posted 01 March 2018 - 09:01 AM

Well, I assumed just that. Sorry if I caused any trouble. But I don't agree that the TDE is 1/4 wave, likely more than that, from the Ronchigrams.
The only time I accept a TDE, is when if it's mild enough, and within the tolerance envelope. Quantification is necessary, and Ronchi won't do that. In other words, if the edge and zone just inside that are either going to be within tolerance or not. If you want to do what Dan recommends, the quantification has to be correct.
   ( I agree with Mladen, this is 5 pages and counting.)
*********
  "If your implying I’m leading him down the wrong path, you are showing you can’t even follow the thread...."

What's this got to do with it? Necessary?
*********
Curt, is the last image in #115 where it's at now?



#123 Pinbout

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Posted 01 March 2018 - 09:25 AM

 

But I don't agree that the TDE is 1/4 wave, likely more than that, from the Ronchigrams.

that's really funny from someone who admits he never uses ronchigrams.



#124 MKV

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Posted 01 March 2018 - 01:33 PM

 

 

But I don't agree that the TDE is 1/4 wave, likely more than that, from the Ronchigrams.

that's really funny from someone who admits he never uses ronchigrams.

 

How does one establish that TDE in a Ronchigram is 1/4 wave, and not 1/5 or 1/8 wave for that matter?! 



#125 MKV

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Posted 01 March 2018 - 01:40 PM

I never fix an edge if I’m oblate

I don't understand why. is there any science behind that statment? Ed Jones has a video on Youtube showing how he parabolized a 12 inch f/7 mirror and fixed the edge, from oblate, in about 3/4 of an hour...to  a 1/10 wave PV 'dynamite'  paraboloid.

 

https://www.youtube....h?v=A7XtObXzutk

 

Hopefully the OP can take some hints from that video and finish his mirror in an afternoon...




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