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My Other Telescope is an 8.4 Meter - Part III: Polishing

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#1 Gork

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Posted 08 May 2019 - 11:25 AM

I've started writing about this aspect of fabricating the world's largest monolithic mirrors a number of times. Each time I get to about ten pages before I realize how truly complex this phase of fabrication is. So, I am going to assume, for the sake of this account, that everything works as planned and there are no side tracks. That won't be true, but if I tell the real story, I'll never get done.

Click here to view the article

#2 kwlf

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Posted 08 May 2019 - 01:34 PM

I just wanted to say how much I've enjoyed this series of articles. I've been visiting the site nearly daily looking for the next installment. Many thanks.


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#3 Gork

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Posted 08 May 2019 - 02:13 PM

Thanks for your message.  I've really enjoyed writing these articles.  It not only brings back old memories but it makes me realize how complex the process really was and how much fun we had.  I envy the folks working there now and I hope they have some sense about what they are accomplishing.


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#4 RickV

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Posted 08 May 2019 - 05:34 PM

This is fantastic reading... hanging on every sentence.  Super High-Tech but where the human element is so important.  No place here for bureaucratic bunglers!

 

Best,

Rick



#5 Gork

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Posted 08 May 2019 - 06:03 PM

Thanks Rick.  It was an exciting job that I miss greatly.  It was a highly technical job, and politics just would not survive.



#6 wyzguy

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Posted 08 May 2019 - 09:08 PM

You've captured your years at the lab quite well Pat.  Maybe there's a writer in you after all!  I see multiple mirrors in some of the images.  I may have missed you referencing it that but how many were going at the same time?



#7 Gork

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Posted 09 May 2019 - 01:07 AM

Remember those old plastic puzzles that had little squares that you would move around that had one empty space?  The Mirror Lab was just like that.  There were times when we had only one mirror in the que, and there were others when we had up to four or five.  Moving them around to make room for processing was a real challenge.  There was no way to store a mirror outside the Lab, so we had to make room inside.  Not all of our mirrors were obtained by buyers as finished mirrors.  For instance, we had one 6.5 meter mirror that was purchased by a foreign government as a cast-only mirror.  They apparently thought they could process the mirror blank.  Since we had contracts for finished mirrors, that one tended to get pushed back in the Casting que.  We were working on finishing the LBT#2 mirror when we got an order from an American corporation for a 6.5 meter mirror that had specifications beyond what we had ever done for an astronomical mirror.  At about the same time we got an order for the GMT center mirror and the LSST primary and secondary mirrors.  For awhile, we were spending almost as much time moving mirrors around as we were processing!  My memory is a bit hazy, but I think the most we ever had processing at one time was five.  That included the Integration Lab which was about the same size as both Casting and Polishing.  That would put one mirror being integrated to its cell, three in the Polishing Lab, and one being cast.  We also had to cast and polish a 5 meter mirror that was ultimately hung face-down up in the test tower that would be used for testing the off-axis mirrors for GMT.  We were all a bit nervous about working ninety feet below a suspended 5 meter mirror!  They finally installed a steel roll-out safety door beneath the mirror that remained closed except during testing.  These mirrors were massive enough that the structural integrity of them could only be calculated.  No actual testing was ever done for obvious reasons.  The safety shield was as much for genuine safety as it was to provide a work environment that we Techs could live with.  It really would take a book to fully describe how that Mirror Lab functions.  Busy days!


Edited by Gork, 09 May 2019 - 07:39 AM.

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#8 macdonjh

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Posted 10 May 2019 - 12:16 PM

I made a mirror like that in my garage once.  But it took several years to get it right.  The Stewart process is better, I think.



#9 macdonjh

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Posted 10 May 2019 - 12:24 PM

Oh, wait, unit error.  My mirror was 8.4 in in diameter, not 8.4 m.  Oops.

 

Hydrofluoric acid is nasty stuff.  It is also used in one process in oil refineries (alkylation, a process to convert low-weight hydrocarbons into higher-weight hydrocarbons for high octane gasoline).  I didn't work in the alkylation unit often, but when I did I had to wear a full PVC suit, gloves and boots, goggles and face shield.  And that was in an area where the bad stuff is supposed to stay in the pipes, we never handled the acid directly.  First aid is now calcium gluconate, but I understand even that can't help if somebody is exposed to too much HF.


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#10 ninelives

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Posted 10 May 2019 - 03:09 PM

Great installment, keep them coming!



#11 Gork

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Posted 11 May 2019 - 04:03 PM

Thanks for all the comments and suggestions.  I'm working on the last installment now.  I need to get back over to the Lab for some more pictures of the Integration process.

Pat


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#12 Gustoresto

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Posted 15 May 2019 - 11:23 AM

Howinhell do ya grab an 8.4m hunk of glass w a steel band around it to flip it? What kept it from slipping out of the band and pray tell how was the assy. grabbed to flip it??   Scary



#13 stubeeef

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Posted Yesterday, 06:27 AM

Cloudy Nights’ version of a hit series, I have been thoroughly enjoying reading each one multiple times. 



#14 Sporocyte

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Posted Today, 06:13 PM

...

Hydrofluoric acid is nasty stuff.  It is also used in one process in oil refineries (alkylation, a process to convert low-weight hydrocarbons into higher-weight hydrocarbons for high octane gasoline). ...

Placid in BR?




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