RE: ATM What's Best Material to Create a Tool?

[Bob Prabowo <BOB@bahana.co.id>]

Hi Mark,

        but I would like to know what is the best material and does it
need to be      heated or cooled and for how long and do I need to seal
it after I placed       the tiles in the material to set?

Some of us would ask you to define "best". The best material for me is
white cement. I use white cement because it can be found easily in any
hardware stores. So my definition of "best" is "availability". I think
you should not worry about the kind of material you use. Judging from
the variety of material people used, I think it doesn't really matter
what material your tool is made of, just make sure that it's strong and
won't deform later.

After casting it, I left my tool untouched for two days. BTW, before
pouring the wahtever-it-is-you-use on the mirror, don't forget to  cover
the mirror with plastic. Guess who forgot to do it. 
After the tool is completly cured, I glued the tiles on it, and applied
thin coat of yellow glue on the back and on the sides of the tool. Left
it untouched for a day to let the glue cure.

         Also what would be an ideal size for the tool? 
Different person will tell you different size. Some use subdiameter
tool, and some use full size tool. I use full size tool both for my 5.6"
(of course) and 13". 

        should any overlapping tiles be trimmed so as not to overlap the
tool. 
If you mean that the tiles on the edge should be cut (trimmed), yes.

        Will I need 2 tools? One for grinding and another for the pitch
lap later       on?
Yes, you're right. You can cast both of the tools now or you can cast
the second tool later. If you decided to cast the polishing tool later I
suggest you make it after grit #220 or after the mirror is close to the
desired depth. Just don't wait until you reach really fine grit. I
casted my polishing tool after I reached 9 micron ( I forgot to make it
earlier) and I must confess that I was affraid that the mirror might get
scratches. I had to do it with extra care and really carefully which I'm
not good at. 

As for thin mirror, you should check Mel's web site, he's the expert and
he has an article on large thin mirror grinding.
Good luck,

Bob P. Sumitro
Jakarta, Indonesia

visit my still-under-construction astronomy and telescope making page:
http://www.geocities.com/CapeCanaveral/Hall/2670/