Re: ATM - The Right Stuff

[Dominic-Luc Webb molmed <Dominic.Luc-Webb@molmed.ki.se>]

On Wed, 18 Jul 2001, Richard wrote:

> When making tile tools and pitch lap foundations of dental stone, I have
> been using saran wrap to cover the bottom of the mold and permit easy
> separation.    This is OK for shallow curves like telescope mirrors, but
> when the curve gets deep, the saran wrap wrinkles and those wrinkles get
> molded into the surface of the casting.

Hi Richard & others,

I guess you and some others in here saw my concrete tool.
The mirror was a 7.25" F/1.5. I used rice paper between
the surfaces. On the one hand, there were some wrinkles
that ended up as creases in the tool. On the other hand,
the were almost completely removed by course grinding.
The creases did not give any problem that I am aware of.
A more serious problem was scratches unrelated to the
creases during fine grinding. Down to 600 grit, the
concrete worked great, but when I got to 9 micron, I
kept getting scratches and went back to 600 to remove
them. I took a breather and put the project aside for
a couple months. Anyway, I don't see the wrinkles
being much of a problem. Do you?

Dominic