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


>From: "Dave McCarter" 
>
>> Make sure you channel that thing before you proceed. The vacuum is
>probably
>> coming from having channels too shallow.
>
>The vacuum that people feel as they fine grind, also called
>"grabbing", is due to the two surfaces being non-spherical. The tool
>and mirror are forced apart by the two hills riding up each other and
>pulling the faces apart. This results because of inadequate fine
>grinding, and not turning the tool with respect to the mirror often
>enough. During fine grinding I use an almost continuous small rotation
>of the tool opposite in direction to the direction in which I move
>around the table. This ensures that the surfaces become truly
>spherical, eliminating "grab".
>
>A raised tile at the edge will increase grinding at the edge and
>create a "mother of all turned edges" that you won't discover until
>you find you can't polish out the edge. Not something you want to try
>to remove by polishing. Check tile tools for loose tiles at every tool
>wash up between grits.
>
>A raised tile in the center will seriously mess up the mirror and
>should be reason enough to remake the tool and go back to 120 grit,
>IMHO. Not an option I would wish on my worst foe!

Or, just pop the tile out and continue with what you are doing. A center
tile missing will have more effect than an edge tile missing but even at
fine grinding, it will have a small effect that can be polished out. A
raised tile is another issue. These are always bad.

>
>Dave

 Also, the issue mentioned Michael Burr. One should get used to
following the rule of having "the edge of the tool touch first and
last". I've even seen a mirror chipped with a lap that was removed
incorrectly! This needs to be a habbit that starts at rough grinding and
follows all the way through. Later
Dwight

--- BBBS/NT v4.00 MP