Re: ATM Why a star lap?

[Joseph Johnston <usc@sover.net>]

Hey Frank,

    Thanks. Your comments have cleared the mud as it were. It makes perfect sense and is
close to my initial thoughts. I would like to see some examples of others construction of
this tool. It sound quite simple though.

--
Joe & the four furry paws of Jenny, the wonder dog,
       in the Aurora filled skies of northwestern Vermont.
               Swanton - The Maple Syrup capitol of the WORLD...


 Ward wrote:

> Joe,
>
> There are several ways to parabolize a sphere, but all entail removing more
> glass from the center than the edge....you >deepen the center<.
>
> One of those many ways is to figure with a "Star Lap" which is no more than
> a star raised above its  surrounding pitch. It is obtained by depressing the
> rest of the pitch with triangles of aluminum foil and hot pressing.
>
> When you do a Wide W stroke with a star lap you are essentially taking off
> glass
> from the middle and 50% zones with less at the 70% and hardly any (only the
> tips
> of the star are in contact) at the 95% zone.
>
> The other use of a star lap is to figure a schmidt corrector. In that
> instance the "star"
> is formed to remove the most glass at the 86% zone with less inside and
> outside that
> area.
>
> The only fault I find with it is the time it takes to make and unmake it
> when it does the
> same job a regular  channeled lap does.
>
> Frank Ward
> Atlanta. GA