From: "Russell Jocoy" 
To: tac{at}i1.net, ATM{at}shore.net
Reply-To: "Russell Jocoy" 


>From: "Bob Walker" 
>Reply-To: "Bob Walker" 
>To: "ATM Group" 
>Subject: ATM Silicone: A Cautionary Tale
>Date: Tue, 19 Aug 2003 21:49:36 -0500
>
>
>I tried a new method of strain testing on my brand-new secondary.  Dropped
>it 4' onto concrete.  The resulting chips out of the edge are perfectly
>semicircular, so no strain, right?  The reason for the drop might prove
>instructive.  Most of you probably know that silicone glue ages once the
>tube is opened, and after a long enough time it won't harden, even though
>it
>remains flowable in the tube.  When it reaches this stage, it usually has a
>semi-granular texture, sort of like tapioca pudding.  What I just found out
>the hard way is that it can look quite normal and still refuse to harden.
>So, the moral of this story is, when gluing something really important,
>like
>a mirror to its cell, don't use an old tube of silicone.  Splurge.  Blow
>three bucks on a new tube.
>All in all, a cheap lesson.  At least it didn't fall six feet onto my
>primary!  ...speaking of which,  my first scope project, underway for over
>a
>year now, is in usable form, though not finished.  An uncoated 16" f/5.4
>mirror works just fine for viewing Mars.  I can see more detail than with
>my
>8" SCT even with the chipped secondary and collimation only a vague
>theoretical concept.  Much refinement to follow!
>
>  *  Best regards, Bob
>*
>          *           *   *
>
>             *         *
>
>

("atm{at}shore.net")

Bob,  I will agree with your statements. Never ever use old silicone
adhesive. Heat and evaporation,
though evaporation does not seem possible inside a plastic tube, will
change the properties of this
fantastic mixture. I have left silicone "caulk" or adhesive in
there tubes for over a year and they will
solidify in high temp areas. I have cut the tubes open to find a perfectly
solid piece of silicon rubber
that can be sliced like a pepperoni. I take these cylinders and bounce them
off my driveway like
super balls. They will bounce very high, I have also used them to stick on
the end of drum sticks
to create a tympany sound on a drum set.  What does this have to do with
what we were talking
about,...nothing just don't use silicone over three months old. Like you
said Bob break out the
wallet and spring for $5.00 or so....unless you are trying to make new
motor mounts for your
Honda.           Russ Jocoy
("atm{at}shore.net")

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