Re: ATM Which Carbo to start with

[Aplanatic@aol.com]

Stathis Kafalis writes:

> I will purchase a pregenerated 24" f/4.2 Pyrex blank from Newport Glass 
Works 
> and intend to grind it with an 18" plaster/tile tool.
>  
>  Do I have to start with grid #80 to make a good mirror/ tool match, or 
will 
> the pregenerated figure will be accurate enough to start with let's say 
grid #
> 180?
>  
>  Can anybody share experience in this?

Hi Stathis:

If you make the tile and plaster tool correctly (where the tiles 
start out in reasonably close contact to the mirror's surface), you 
can use #220 or even #320 to set in the tiles as long as the tiles 
are not more than about 35 mm in size.  If after a half an hour of 
grinding it looks like the tool will take a long time to come into 
contact, switch to #120.  At this stage it's OK if ~15% of the tiles 
are not in good contact as long as the offending tiles are more or 
less uniformly distributed over the face of the tool.  Best of luck.

Dave Rowe.