From: "Dwight K. Elvey" 
To: atm{at}shore.net
Reply-To: "Dwight K. Elvey" 


Hi
 I recommend making a cement or plaster base for your
polishing tool. You can use your mirror to match the curve. Put some
plastic wrap between the surface of the mirror and the cement or plaster.
Use masking or duct tape to make the rest of the mold. Make the surface of
the tool as flat as you can. Coat the tool with epoxy before pouring the
pitch.
Dwight


>From: "Kartik Patel" 
>
>Hello, all
>
>This is an update on the 10" (well, 9.5", actually) mirror I am in the
>process of making, and a query.
>
>The grinding process is over. The last stage (1200 mesh SiC) was
>completed some time ago. The focal length is 57", corresponding to
>f/6, which was the aim. The tool was made of  ordinary cement with
>glass tiles; the channels between the tiles were filled with candle
>wax. The wax was remelted and refilled between stages, and completely
>replaced before starting the 600 grit stage.
>
>There are no visible scratches or pits on the blank and so, hopefully,
>it can proceed to the polishing stage.
>
>Having not made a base for the polishing lap, I am toying with the
>idea of using a circular piece of plywood, cut to the size of the
>blank, as a base instead of cement or plaster. Since the central
>portion won't be elevated, the plywood being plane all over, I am
>thinking of placing a two millimetre thick circular piece in the
>centre, having a radius of two inches or so. The pitch will be poured
>over this and pressed with the blank in the usual way.
>
>I remember reading (perhaps on the list?) that this procedure can be
>used to make a base for the polising lap. Or should I go the usual way
>and cast a plaster or cement base?
>
>Sincerely,
>Kartik Patel,
>http://www.geocities.com/letapk/index.html
>kpatel{at}hotpop.com
>
>
>
>
>
>

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