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Curt is the worst mirror maker ever!

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#76 T Madden

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Posted 15 February 2018 - 04:54 PM

Latest progress report as of 2/14/2018.

 

I did about two hours by hand with the spin polishing machine rotating about 3RPM.  90% diameter tool.  Ten minutes polishing with 1/3 to 1/2 COC strokes mostly over center.  Ten minute cold press and then repeated.  Alternated sessions with TOT and MOT.  Used 10 lb weight when tool was on top.  About 30 strokes per minute.  Did these cycles for a total of two hours.  12.4 inch diameter mirror, 125.4 inch ROC, and f/5.

 

This is a Foucaultgram slightly out beyond ROC:

 

 

This is the Ronchigram out beyond ROC to about 0.37 inches:

 

 

==========================================

 

I went back to the spin polisher.  All TOT.  Started with 20 minute warm press.  10 minute spin followed by 10 minute cold press.  Machine running at 40 RPM.  About 30 lbs weight.  Moved arm so tool center rotated over 10% to 90% of mirror radius.  Cycled back and forth by hand at 3 second period.  A slurry of CeO & water.

 

Here is the knife edge about 3/4 inch inside ROC with diffused LED light source:

 
 
Knife edge at about same point as above but with unfocused/non-lazing laser point source:
 
 
I used zoom to get a closer look at that edge above:
 
 
Foucaultgram just slightly beyond ROC.
 
 
Ronchigram out beyond ROC to about 0.37 inches:
 

 

======================================

Should I keep working to reduce that edge?  Should I work on getting it closer to a sphere?  How?

 

Curt

That looks like good progress to me!



#77 charlievictor102

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Posted 18 February 2018 - 10:40 PM

Better?

 

20180218cejpg

 

Curt

 

Update:

12.4 inch mirror, ROC = 125.4 inch, Pyrex, Ronchi 85LPI, Positioned approx 0.37 beyond ROC.


Edited by charlievictor102, Yesterday, 07:20 PM.

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#78 Pinbout

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Posted 18 February 2018 - 11:25 PM

Again... is it inside or outside 4.gif bangbang.gif fingertap.gif  foreheadslap.gif

 

lol.gif



#79 charlievictor102

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Posted 18 February 2018 - 11:27 PM

Again... is it inside or outside 4.gif bangbang.gif fingertap.gif  foreheadslap.gif

 

lol.gif

 

Sorry. Outside. 



#80 mark cowan

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Posted 18 February 2018 - 11:29 PM

Better either way.


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#81 Pinbout

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Posted 18 February 2018 - 11:46 PM

So what’s your next move?

 

do you know what your looking at and what you want to do next?



#82 charlievictor102

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Posted Yesterday, 06:38 AM

So what’s your next move?

 

do you know what your looking at and what you want to do next?

 

I’m looking for suggestions on how to proceed. 

 

Curt



#83 T Madden

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Posted Yesterday, 08:23 AM

It gets better every time! Edge zone is down a bit, 50% is up a bit, slight hole in center.  Have a look at this: http://schmidling.com/etron.gif

Whatever you are doing is working, but proceed carefully now, you are getting close to spherical. Maybe less added weight now. 



#84 Pinbout

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Posted Yesterday, 08:39 AM

It gets better every time! Edge zone is down a bit, 50% is up a bit, slight hole in center.  Have a look at this: http://schmidling.com/etron.gif

Whatever you are doing is working, but proceed carefully now, you are getting close to spherical. Maybe less added weight now. 

 

he does have a lot of ring zones but I wouldn't call it a hole, like a typical hole.

 

 

are you going to use the machine or doing it by hand?

 

I'd start parabolizing...



#85 T Madden

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Posted Yesterday, 09:01 AM

 

It gets better every time! Edge zone is down a bit, 50% is up a bit, slight hole in center.  Have a look at this: http://schmidling.com/etron.gif

Whatever you are doing is working, but proceed carefully now, you are getting close to spherical. Maybe less added weight now. 

 

he does have a lot of ring zones but I wouldn't call it a hole, like a typical hole.

 

 

are you going to use the machine or doing it by hand?

 

I'd start parabolizing...

 

Curt's not so bad now, LOL!


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#86 charlievictor102

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Posted Yesterday, 07:41 PM

Better either way.

Thanks Mark.

 

I tried long COC strokes by hand and that seem to make the edge even worse.  I'm pretty sure that I can rule out the edge not being polished out as I have got the edge better then screwed it up several times.

 

Then I got pretty good progress using your method written in this thread:

 

https://www.cloudyni...a-perfect-edge/

 

Done by machine.  89% Tool.  15% mirror diameter tool overhang.  30 lbs weight on top of tool.  Spin polishing machine at 40 RPM.  Spritz water or CeO/water every 5 minutes.  I probably did this for two hours.

 

That left a few rings but seem to work the edge into better shape (I did not post pictures of that here). 

 

I then reduced the overhang, went to 10 lbs  and ran it for 20 minutes.  That put a few more rings but reduced the ring magnitude overall (see picture in post #77.

 

I'm in the process of some mods to my tester and can't get that "drawn-inside-ROC-past-the-mirror-center-with-a-small-pinhole-test" for you.

 

Do you think the edge is good enough?  How should I proceed?

 

Curt



#87 mark cowan

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Posted Yesterday, 10:18 PM

Well huzzah for that then.  The rings won't matter at all if figuring takes very long.  If it's a slow mirror you'll need to work them out first though.

 

If you can do a Foucault with good illumination of the diffraction ring most people will be satisfied.  ;)  But in the Ronchi image it looks fine.



#88 charlievictor102

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Posted Yesterday, 11:07 PM

...If you can do a Foucault with good illumination of the diffraction ring most people will be satisfied...

 

This Foucault is of the mirror in same state as Ronchi in post #77.
 
20180219a

 

Most of those rings null out at the same ROC.

 

Is this what you meant?

 

Curt



#89 charlievictor102

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Posted Yesterday, 11:28 PM

Here is a video using the Windows 10 Camera app.  That app seems to have some exposure control.  I can't seem to be able to do that with any software I write.  Here I'm cutting into the light path with the knife edge.  Pretty close to ROC.

 

https://youtu.be/0qtGJTydkus

 

Curt



#90 Dale Eason

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Posted Yesterday, 11:32 PM

 

...If you can do a Foucault with good illumination of the diffraction ring most people will be satisfied...

 

This Foucault is of the mirror in same state as Ronchi in post #77.
 
 

 

Most of those rings null out at the same ROC.

 

Is this what you meant?

 

Curt

 

 

No, he was talking about the bright ring that forms all around a mirror with a good edge.

 

Those rings are very small defects that a good mirror maker would eliminate.  You don't have enough resolution in Foucault data reduction to see their ROC affect on the surface of the mirror most of the time.   With experience like Mark has one would know if you have enough figuring to do that would remove them.  If not you have to address them yet.  I think one working with machine knowledge would just lit the spin polish remove them.  So for them it would be no big deal.  For a beginner that is another chapter of your learning experience.

 

Dale 


Edited by Dale Eason, Yesterday, 11:33 PM.


#91 mark cowan

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Posted Yesterday, 11:39 PM

 

...If you can do a Foucault with good illumination of the diffraction ring most people will be satisfied...

 

This Foucault is of the mirror in same state as Ronchi in post #77.
 
 

 

Most of those rings null out at the same ROC.

 

Is this what you meant?

 

Curt

 

That looks fine in terms of the edge.  For an f/5 the rings will likely be long gone by the time figuring is done. 

 

But not necessarily, as Dale says.  If you can clean it up to where they don't look like they stick up or down  (i.e. no annular zones at all) it'd be best.


Edited by mark cowan, Yesterday, 11:40 PM.


#92 charlievictor102

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Posted Today, 12:00 AM

Okay.  Here is where I am:

 

Virtually no experience.  But I have that (zero) experience over about 50 years since that is when I started my first telescope in grade school.  So far unsuccessful.

 

Here are the books in my library:

  1. How to Make a Telescope, Jean Texereau, 1919.
  2. All about Telescopes, Sam Brown, 1967.
  3. Build Your Own Telescope, Richard Berry, 1994.
  4. The Dobsonian Telescope, David Kreige & Richard Berry, 1997.

I have a "Fixed Post" polishing machine.  I can adjust its speed from 3 RPM to 60 RPM.  I can run it stand alone or use it manually as required.

 

Here are the Tools at my disposal:

 

Im Such a Tool

 

They are:

  1. 11 inch, 89%
  2. 8.8 inch, 71%
  3. 4.8 inch, 39%
  4. 3.5 inch, 28%
  5. 2.8 inch, hockey puck.

Most of these are Gugolz #55.  Tool #1 is a mix of #55 and #64.  My garage is about 60 degrees F.  About 40% humidity.  I have lots of #55.

 

I can make any additional tool as necessary.  I could redo the pitch on any of these.

 

I'm looking for guidance on where to go from here.  In particular:

  1. Machine or manual?
  2. Which tool?
  3. What polishing/figuring stroke?
  4. Thin versus thick; dry versus runny CeO?
  5. How much weight?
  6. How fast?
  7. How long?
  8. Warm/Cold press, polishing session cycle timing?

Any guidance would be greatly appreciated.

 

Curt



#93 mark cowan

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Posted Today, 01:28 AM

You're not far off it.  If you can do a small manual stroke with the fixed quill (post) polisher the rings should dissipate doing what you were doing.  These pictures are from fixed position spin polishing but with asymmetric faceting (probably just razor scratches for "facets" 3 way triangles non centered).

 

To give an idea to compare with yours this is the start for figuring:

 

 

temp1.jpg

 

 

temp2.jpg

 

 

 




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