Post by Chicago Astronomer - Astro Joe on Apr 5, 2013 13:36:51 GMT -6
Replacing the 90mm Finder Scope Bases on the C11
04 April 2013
(Simple Corrector Plate removal becomes a complicated Mod project)
This is really two stories in one - one project that should have been a straight forward job and a couple of hours tops. The other, something I encountered that stopped me in my tracks in starting that simple job. I always anticipate complications, but not like this.
From day one, these generic bases that holds up the 90mm Meade finder scope and rides on top on the C11 - have been substandard....
Full story here:
astronomer.proboards.com/index.cgi?board=Equipment&action=display&thread=2963&page=1
Wobbly and sloppy, the refractor once fell out of the base, crashing to the ground and causing minor damage to the Dew Shield...
Master Crafter and fellow Astronomer Rick came to my rescue and made me neat bases for the brackets he made me earlier. Now, a matched set awaited to be mated, but this needed the C11 to be taken apart to install. 2012 was a tragic year for the Chicago Astronomer...and I needed the C11 whole for the Chicago Astronomer and Chicago Park District Star parties we worked. By the time the season was over, it was just too cold - and the workshop is not heated...
April is a good time to install this bases....and besides, the C11 needed a good cleaning after serving our fans last year...
Yep, the corrector needs some heavy cleaning.
Chicago Astronomer Forum member Mo, (Andy) suggests that the secondary housing be checked for eccentricity...
In actuality, the housing is ever so slightly off. I'll correct it when I re-assemble.
We have gone through this process of dis-assembly before without a hitch..
The Corrector Plate retaining ring gets removed quickly, but....when I attempt to remove the corrector plate...it does not budge. I apply some force....nothing. I tug on the secondary housing some more - stuck on tight.
What the hell!
During the previous dis-assemblies, the corrector plate came off without struggle. Nothing has changed since. Too clean of a plate....heat/cold...new paint vapors???
I examine the circumference of the plate...and all looks ok...
I can easily move the spacers around the edge of the plate...but the hunk of glass just won't move! I use popsicle sticks to wedge and pry around the edge of the plate...
I tap all around the edge with the sticks...and nothing.
Damn.
I resort to giving the secondary one more strong tug....
...and the secondary came apart!
The cork laying in between the plate and the front cell has bonded tight. Well, at least now, I can use the opening as a place to grab and pull.
Nothing.
I use my closed hand and rap from the inside out...got to loosen now.
Nothing.
?
I need to break this Satan seal somehow...so I grab my 91% Alcohol and apply two cap fulls via a Q-tip around the edge...
I can see the alcohol work its way under the plate and saturating the cork. I tug and nothing. I apply another cap full and wait a bit. I gently tug at the plate and I can see the vacuum created, sucking in the alcohol where it's needed. Much more play now, but still won't release.
After about 10 minutes, I give the plate small repeated tugs....and I hear it before I see movement. What ever held this plate tight - got beat down and finally released...
The back side of the cork was attached to the cell housing with double sided tape...and this is what finally let go...not the bond to the plate!
Daang!
I do not know what happened here and why it grabbed on tight, but I will have to remove the stuck on cork and replace it with new. This took much longer than I anticipated and it was already 11:00 pm. As I need to awake by 5:30 am...I was beat. I'll pick up tomorrow evening and left the tube on the workbench.
But wait....
But, with all that shaking, tapping and alcohol - the primary got dirty...a lot.
It just doesn't stop...
The alcohol left some splatter on the primary and I needed to get it off quick before it sets. Using the cleaning solution I made and have been using, I use a great many cotton puffs and lift the crud off...leaving a pretty decently clean mirror.
(Yea yea...we all hear about how "you got to leave the mirror alone for Christ sakes!". But if done carefully and smartly, all is good - but we will see.)
Setting the primary and corrector plate in clean new pizza boxes, I decide I might as well install a bracket base and have some sense of accomplishment this evening...
Out come the old raggedly bases....and in with the new...
Master Crafter/Astronomer Rick milled these bases and dovetails to tight tolerances - with with the circumference bend of the OTA too. With the Metal cleaner/conditioner to remove oxidation and give the parts a great luster...the two pieces slide against each other like buttered teflon... ;D
Back to this project tomorrow for part two.....