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How Clean does Secondary Holder Need to Be?

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#1 Scott Regener

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Posted 18 April 2019 - 10:55 AM

I've got my new secondary mirror all ready to go for my Orion XT10i Dobsonian. I pried the old one off the holder (which was a job - how in the world can that tape fail?) I have aquarium silicone caulk for doing the 3-point attachment of the new mirror to the holder. But there's still a lot of sticky residue from the old foam tape. I've attacked it with Goo Gone and rubbing alcohol and it's still there. Not horrible, but not clean. How clean do I need to get this before doing the attachment? Any advice on a better way to get the remnants off? I'm almost thinking sandpaper, it's sooooo difficult.



#2 KerryR

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Posted 18 April 2019 - 11:11 AM

For a fail safe bond, it'd be probably be best to get the old stuff off- obviously, it sucks when the secondary falls on to the primary. I suspect the issue is a super-thin layer of plastic that's between the remaining foam the glue that holds the stuff down- it makes it so that solvents can't contact the glue. Try scraping with a razor blade and heat (most foam tape failures occur in hot conditions, like the back seat of a car on a sunny day, so I'd expect this to help). You could also use a sand paper and solvent combo- put the paper down on a flat surface, pour on a little solvent, hold the beveled mirror holder surface flat on top of that, and rub/sand. Once the surface is free of all goo/solvent residue, clean the surface thoroughly, finish with an alcohol wipe or two just before gluing (obviously, be sure the surface is completely dry.)

 


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#3 TOMDEY

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Posted 18 April 2019 - 11:52 AM

Xylene (Xylol), Carbon Tetrachloride, Acetone...

 

The Xylene, available at hardware or paint store, is generally great on contact cement and such.    Tom



#4 ngc7319_20

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Posted 18 April 2019 - 12:42 PM

I like WD40...  Dont think its carcinogenic...


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#5 KerryR

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Posted 18 April 2019 - 01:33 PM

I like WD40...  Dont think its carcinogenic...

I forgot about WD40! I've had great luck with that with sticky stuff! Worth a try, and won't disolve paint or plastic, as some solvent might.



#6 daquad

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Posted 19 April 2019 - 02:24 PM

Acetone will dissolve plastics, so that may work as TOMDEY has suggested.  If that fails, lacquer thinner should do it.  It dissolves the surgical gloves I wear if I get any on them.



#7 Vic Menard

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Posted 19 April 2019 - 02:49 PM

Xylene (Xylol), Carbon Tetrachloride, Acetone...

 

The Xylene, available at hardware or paint store, is generally great on contact cement and such.    Tom

Is Xylene a petrochemical? Carbon Tet?

The only reason I ask is Mike Lockwood has noted that certain petrochemical solvents/cleaners can penetrate mirror coatings and make the glass substrate impossible to recoat (requiring repolishing to remove the contaminant). Reference http://www.loptics.c...mirrorcare.html

 

I don't think there are any issues with Acetone or alcohols...   



#8 Vic Menard

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Posted 19 April 2019 - 02:56 PM

WD40 is also (less than 25-percent) petroleum base oil  https://en.wikipedia...rg/wiki/WD-40. 

 

Edit: Obviously, these petrochemical products can be used on the unaluminized back of a first surface mirror. But great care should be taken to ensure that the front surface, or even the edge of the front surface, is not contaminated in the cleaning process. I've had good results with a sharp blade and acetone when removing adhesive residues from glass and metal surfaces. 

 

You can also rotate the 3 contact points 60-degrees and be guaranteed "fresh" surfaces to glue the two parts together. I also recommend a safety tether that is glued to the back of the mirror and to the secondary holder, just as a "secondary" means of attachment (the pun is unintended).


Edited by Vic Menard, 19 April 2019 - 03:09 PM.


#9 TOMDEY

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Posted 19 April 2019 - 04:59 PM

Xylene (Xylol), Carbon Tetrachloride, Acetone...

The Xylene, available at hardware or paint store, is generally great on contact cement and such.    Tom

Is Xylene a petrochemical? Carbon Tet?

The only reason I ask is Mike Lockwood has noted that certain petrochemical solvents/cleaners can penetrate mirror coatings and make the glass substrate impossible to recoat (requiring repolishing to remove the contaminant). Reference http://www.loptics.c...mirrorcare.html

I don't think there are any issues with Acetone or alcohols...   

Meeehhh... could be! On the other hand...

 

MIRROR-ABUSE EXPERIMENT: >>>

 

Well, being my usual curious. buffoonish, risk-taker self, I intentionally took every chemical solvent in the stable to a perfectly nice 75-cm Primary Mirror that needed recoating. I splashed on every can and bottle of stuff from the hardware store and chem lab that I could sneak off with. Although I claimed to have used them all, I actually did not splash on these three >>>... I may be stupid, but not that stupid... yet. Then, just to be safe, I took an exploratory sniff of each and flushed them down the bathroom sink. Note: Potassium Cyanide does not smell like burnt almonds. Rather, it has just what I can describe as a "chemical smell" no other way to describe it. When I noticed that I was actually getting a good whiff of it, I put on the lid and went out on the veranda for several gulps of fresh air. [Honest, that's a true story from my days and nights in Panama!] Suffered no ill effects... guess it just wasn't enough to kill me. And the earth was spared the loss, for then.

 

Anyway, the upshot was that I then took the mirror in for recoating. Came out beauteous and stuck it back in the telescope, working just fine. The substrate is Corning Pyrex. Maybe other glasses wouldn't have tolerated that abuse as gracefully.

 

This, and other anecdotes, are brought to you by the letter Alpha.    Tom

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#10 TG

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Posted 20 April 2019 - 01:36 PM

Xylene (Xylol), Carbon Tetrachloride, Acetone...

The Xylene, available at hardware or paint store, is generally great on contact cement and such. Tom


Carbon tetrachloride is not a nice chemical

https://en.m.wikiped...n_tetrachloride
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#11 TOMDEY

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Posted 20 April 2019 - 03:20 PM

Carbon tetrachloride is not a nice chemical

https://en.m.wikiped...n_tetrachloride

Yep...?! And I used to intimate with such chemicals up to my elbows, when I was a kid! No rubber gloves, no breathing avoidance... Heck, I actually thought it had a charming bouquet, so would sniff it every time I opened the pint bottle. My sister thought my bottle of mercury was toxic... so she poured it down the bathroom sink... right where we routinely washed our faces and brushed our teeth. Me thinking... "that's never going past the trap... for a long long time..." But said nothing, else get slapped.

 

Then we'd go over to the switching station and play chicken with the railroad cars. The guards would often chase us away. Eventually one kid got killed; I wasn't there that day and sorta avoided the place after that. They said he "fell from a railroad car" but I always thought they were just being kind, to the family. More likely he was showing off and guessed wrong... Nother guy, cause of death was "a fishing accident" which seemed strangely undetailed and generic. And that guy too, was a notorious risk-taker. To the point that we... liked and admired him, but also considered him rather nuts, candidate for a short existence, bowing out ~doing what he loved~ Never heard any details, regarding that premature demise!

 

That was pretty much the safe ghetto families of the 1950s. And what has made me the manly man that I grew into!

 

Well... it's a beautiful sunny late afternoon! Just finished supper and will go out for a relaxing hike thru the woods. Planning on Ehhh... three miles in and three miles out. Nice and minimalist, no phone, no ID, no camera, nobody else, nice and remote... just me and nature.    Tom


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#12 Jon Isaacs

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Posted 20 April 2019 - 04:37 PM

Yep...?! And I used to intimate with such chemicals up to my elbows, when I was a kid!

 

 

I have been intimate with a number of toxic chemicals in my life time.  Tetrachloroethylene was one.  A broken gallon jug in a small compartment in the stern of a ship probably has taken a year or two off my life expectancy.

 

Chemicals like Xylene (Xylol), Carbon Tetrachloride etc should only be used after reading the appropriate MSDS, carbon tet is a liver toxin.  

 

https://en.wikipedia...n_tetrachloride

 

WD-40 is a what I would try.  It also removes pine pitch from your hands.

 

Jon


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#13 Earthbound1

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Posted 08 June 2019 - 01:05 AM

I'm definitely in Tom and Jon's "club"... I used to play with a jar full of mercury... Took some to school, grew crystals of potassium ferrocyanide, been elbow deep in LOTS of solvents like MEK, benzene and methylene chloride... Can't count the times I washed stuff in gasoline with bare hands to degrease 'em... Feeling great at only 52 though... Anyway I still, especially now, play with acetone which for $1.65 you can get a bottle of 100% from Dollar General beside the nail polish remover as it IS a great solvent and a primer for PVC that's way cheaper than that purple stuff... I like WD-40 and P.B. Blaster too... Anyway, yep I'm lucky to still be alive! Nevermind the weapons of mass destruction me and my friends built in our pre-teens and teenage years that would earn you a one way ticket to Guantanamo Bay today...

Edited by Earthbound1, 08 June 2019 - 01:10 AM.



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