ATM plaster, glue and glass

[astillma@nit.AirTouch.COM (Anthony Stillman)]

Richard Schwartz


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You wrote:

I am the guy who asked about the software.  I have been trying to use IRT 
(Interactive Ray Tracer).  It has optimization and all that good stuff, but
if you as much as sneeze, you will have to reboot  your computer!  Too bad;
it could teach us a lot about telescope design.

My application is to model that folded gregorian design that was touted here
a week ago.  I believe that there will be severe problems with coma and
astigmatism because of the need for an off-axis ellipsoidm, but I want to
check it out before ragging on the inventor.

You also wrote:

When you mix your plaster, you also mix in white glue?  In what proportions?
 I like the idea of mixing something into the plaster; that way it can never
peel off.  But how do  you get the white glue deep inside the tool to dry
out and harden?  Does the heat from the microwave degrade that stuff?

In recent experiments with dental stone, I discovered the ideal sealant that
pitch will stick to perfectly. It is @
a89^ ,   To get it to penetrate into the dental stone you just dilute it in
.&% f!1a**).   And you let it bake overnight in the oven at about 200
degrees F to dry it out.   I wonder if my discovery might work on ordinary
plaster.

Have you considered molding the tiles into the plaster?  That is what I am
doing; I don't use any epoxy or other glue to hold them on.  I have never
lost a tile because of this.  I use 1" square unglazed urinal tiles from
home depot, and I don't even urinate on them!

One thing you best not even waste brain waves on: urethane or polyurethane. 
The slightest nick in the coating allows water to penetrate, and soon the
urethane is peeling off.
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With regard to IRT.  I agree, it carshes if you breath, and even the Valcun nerve pinch 
(ctrl-alt-del) won't bring the computer back, I actually have to push reset.  Which has 
had the effect of making me clean up the pile in front of my computer enough to reach the 
reset botton.  IRT does have some benifits, so I still use the demo copy on occasion, but 
no way would I spend $495 for this piece of ^&*#(%.

VOB on the other had, while it still crashes, is a dream to work with.  I love it, and I 
will buy a full version.  I recommend others do also.  Good code needs to be supported so 
that there is more of it.

Plaster and glue.  I experimeted with the glue thing several times before getting it 
right.  I bought two of thoes big bottles of white glue from Home Despot and tried a 
quarter then one half with small batches (enough for an 8"-10" a couple inches thick)  
The second batch worked well, but not due to the amount of glue, rather because I added 
the glue after adding and mixing in the water.  The first actual tool I made with glue 
was for a 12.5".  It was about 13" in diameter and 2+ inches thick.  For this I used a 
hole bottle (I had plaster left over) It was too much glue, got too sticky and was hard 
to clean up, but it still worked.  I didn't use the microwave to cure this tool, just 
left it in the oven for a week.  I have a gas oven so with the pilot light its always 
about 100 degrees (F)

Other glue and stuff.  I have tried urethane, both water and non-water based, for 
coatings.  You are right, they are awful.  I even tried using water based urethane in 
plaster of Paris, but I made the mistake of not first mixing in water.  Since I already 
new the process involved in converting powered gypsum to crystalized gypsum, I should 
have know better than expect it to work. Hey, everyone makes mistakes.  I may try this 
again, someday. 

I have never tried casting in tile as you explained.  I did however onece, (this is 20 
years ago now) fire a porcelain tool with a hex tile impression pressed in.  Worked 
pretty well. The clay curved in firing, but then so did the mirror, also made of 
porcelian.  I only now again have access to the equipment need to work with high fire 
clays.  Maybe I'll try it again, right after I finish that...

Last, its so close to Riverside I can taste it, I agree that the cross Gregorian may have 
problems with abberations.  I've been assurred not, buuuutttt... Anyway please don't let 
my nature preclude anyone form tring it.  After all I still have problems dealing with 
the twin paradox.

Riverside, Riverside, Riverside, Riverside....

Anthony

PS    I'm sorry about the lack of <CR> <LF>.  I'll write something to add
them.  I'll even distribute source.