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Curt is the worst mirror maker ever!

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124 replies to this topic

#1 charlievictor102

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Posted 07 February 2018 - 08:01 PM

So I messed up my 12.5 inch mirror yet again.  Horrible turned-down-edge.  I'm going back to the spin polisher which has been pretty effective in bringing it back to a sphere before.  After I bringing it back, I'm hoping to use the "Wisdom of the Masses" here and seek suggestions on how I should go about parabolizing it.

 

In the meantime, here is a video of my setup:

 

https://youtu.be/L8rwStxM_HQ

 

 

Curt


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#2 Pinbout

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Posted 07 February 2018 - 08:10 PM

I wanted to see the Ronchi / foucaultgrams

 

rulez.gif


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#3 charlievictor102

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Posted 07 February 2018 - 08:12 PM

I wanted to see the Ronchi / foucaultgrams

 

rulez.gif

Oh.  Will do.



#4 Pinbout

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Posted 07 February 2018 - 08:20 PM

Couldnt be worse than

 

med_gallery_106859_4364_1407449854_26407


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#5 charlievictor102

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Posted 07 February 2018 - 08:22 PM

Couldnt be worse than

 

 

No.  It has never been that bad. bow.gif

 

Curt



#6 Mitrovarr

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Posted 07 February 2018 - 08:50 PM

Couldnt be worse than

 

med_gallery_106859_4364_1407449854_26407

Ronchigram or Winamp visualization? lol.gif


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#7 starcanoe

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Posted 07 February 2018 - 09:22 PM

Coulter? Curt?

 

They both start with C......just saying....

 

If only your last name started with a Z....


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#8 Pinbout

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Posted 07 February 2018 - 09:32 PM

 

Couldnt be worse than

 

med_gallery_106859_4364_1407449854_26407

Ronchigram or Winamp visualization? lol.gif

 

Double pass autocollimation so it looks 2x’s as bad

 

and if you count there’s 3 major ring zones and it does null

 

4hours later of wide zigzag

but it’s on the wrong side of a sphere

 

gallery_106859_4364_1407452290_28934.jpg


Edited by Pinbout, 07 February 2018 - 09:38 PM.


#9 charlievictor102

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Posted 07 February 2018 - 09:56 PM

So this is the TDE before I went back to spin polishing.  This is about 1 inch inside of ROC.  Knife edge from the right.

 

20180207 TDE1

 

Here is after 45 minutes spin polishing:

 

20180207 TDE2

 

TDE better?  Should I continue?

I will worry about the raised center a little later.

 

Curt



#10 mark cowan

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Posted 07 February 2018 - 10:06 PM

Ronchi


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#11 Chuck Hards

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Posted 07 February 2018 - 10:26 PM

That looks exactly like my daughter's cat Zoe's markings, in polar projection.  I've never seen a mirror that... strange.

 

 

Couldnt be worse than

 

med_gallery_106859_4364_1407449854_26407


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#12 Pinbout

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Posted 07 February 2018 - 10:32 PM

 

That looks exactly like my daughter's cat Zoe's markings, in polar projection.  I've never seen a mirror that... strange.

 

 

Couldnt be worse than

 

med_gallery_106859_4364_1407449854_26407

 

Thank you


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#13 Chuck Hards

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Posted 07 February 2018 - 10:36 PM

I really am impressed!  That's just a remarkable pattern.  Is there a story behind it?  Or just a surprise?  I've had horrible ones.  More than I care to remember.



#14 Pinbout

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Posted 07 February 2018 - 10:42 PM

I made 2 8” f3.5’s 5/8” thk plate glass. 

The ring zones are polishing pads on penny tool spin polished for an hour

 

similar to this but this is roc not dpac

 

gallery_106859_4364_1407450101_26666.jpg



#15 phonehome

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Posted 07 February 2018 - 10:53 PM


med_gallery_106859_4364_1407449854_26407

 

Sure it's not a Rorschach test we're looking at?

 

PH


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#16 charlievictor102

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Posted 07 February 2018 - 11:00 PM

Ronchi

Well...okay.  If I must.

 

This is after about 20 minutes more spin polishing than my last post.

 

The mirror diameter is 12.4 inches.

The Radius of Curvature is 125.3 inches.

The Ronchi grating is 85 LPI.

The Ronch grating spans the diffused LED light source.

 

My X-Y stage is kind of limited in the direction toward the mirror: max 0.407 inches.

 

Close to the center null as I could get:

 

20190207 Ronchi 000

 

Then out to 0.123 inches:

 

20190207 Ronchi 123

 

Then out to 0.246 inches:

 

20190207 Ronchi 246

 

Then out to 0.370 inches:

 

20190207 Ronchi 370

 

So any other info I should provide?

 

Curt


Edited by charlievictor102, 07 February 2018 - 11:01 PM.


#17 Pinbout

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Posted 07 February 2018 - 11:07 PM

You have to fix the edge then reduce the hill



#18 charlievictor102

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Posted 07 February 2018 - 11:26 PM

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?

 

That is why I thought that the knife edge inside ROC, cut about 25% into the image, was a better tell. 

 

I plan to continue machine spin polishing tomorrow. I’m seeing pretty good progress with the TDE doing that. 

 

Curt



#19 mark cowan

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Posted 07 February 2018 - 11:41 PM

Not in this case, the TDE is, uhm, striking.  It will take a while spin polishing to clean the edge up but it will do it.  


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#20 Mark Harry

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Posted 08 February 2018 - 05:18 AM

+1
M.



#21 pjmulka

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Posted 08 February 2018 - 08:31 AM

So this is the TDE before I went back to spin polishing. This is about 1 inch inside of ROC. Knife edge from the right.



Here is after 45 minutes spin polishing:



TDE better? Should I continue?
I will worry about the raised center a little later.

Curt

Reference the shadowgrams in post # 9. I don't know why it didn't bring them along when I quoted that post.

 

Sorry to the OP not trying to hijack your thread just trying to learn from it.

Could someone point out the TDE please. I'm not sure what to look for in those photos.

Also they both look completely identical to me...what am I missing? Is it the lack of a outer ring?


Edited by pjmulka, 08 February 2018 - 08:36 AM.


#22 PrestonE

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Posted 08 February 2018 - 08:59 AM

Hola Charlie,

 

One problem that I see in your video...

 

Your weight is not centered and that will cause uneven wear and possibly

affect the TDE...

 

Center you weights over the tool and then attack the next plan.

 

Nice machine, by the way.

 

Best Regards,

 

Preston


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#23 gregj888

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Posted 08 February 2018 - 11:13 AM

Someone smarter than I am will have to add to this, but I question whether you have a turned edge.  How far does the lap extend over the edge of the mirror and is it big enough for initial polishing?

 

I was so worried about a turned edge early on, I under work the edge on my 20".  Foucault looked good but something strange in the ronchi.  Zambuto even looked at it at the Bellingham conference.  We finely figured out I had a tight step 1/4"-1/2" in from the edge.  ROC was correct at the edge and the next zone in, but they two zones were not on the same plane.  After that I've been pretty convinced may "turned edges" are "under worked edges" ... still flat, but much easier to correct.  A Bath interferometer should tell the difference, Ronchi give a hint but Foucault measurements may not (shadow should).

 

To me the shadows in message 16 support this.

 

Someone with experience spin polishing, please comment...


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#24 charlievictor102

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Posted 08 February 2018 - 11:36 AM

 

So this is the TDE before I went back to spin polishing. This is about 1 inch inside of ROC. Knife edge from the right.



Here is after 45 minutes spin polishing:



TDE better? Should I continue?
I will worry about the raised center a little later.

Curt

Reference the shadowgrams in post # 9. I don't know why it didn't bring them along when I quoted that post.

 

Sorry to the OP not trying to hijack your thread just trying to learn from it.

Could someone point out the TDE please. I'm not sure what to look for in those photos.

Also they both look completely identical to me...what am I missing? Is it the lack of a outer ring?

 

I’m probably not the one to answer since I have very little experience but these foucaultgrams were taken with the knife edge considerably inside the radius of curvature. I then cut into the returned beam about 25% across the mirror. If the mirror was perfectly spherical I think that vertical transition line would be straight. But notice how it bends at the top. More so in the first picture than the second. That shows the TDE. 

 

Curt



#25 charlievictor102

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Posted 08 February 2018 - 11:41 AM

Hola Charlie,

 

One problem that I see in your video...

 

Your weight is not centered and that will cause uneven wear and possibly

affect the TDE...

 

Center you weights over the tool and then attack the next plan.

 

Nice machine, by the way.

 

Best Regards,

 

Preston

Thanks for the feedback.

 

Agreed that the weight is not centered. I forgot to put the rubber pads between the weights. They walked a bit in the video. 

 

I copied the machine from watching the Gorden Waite videos. 

 

Curt




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