RE: [ATM] More Mirror Disasters! Pitch movement

["Thomas" <tomjan@ozemail.com.au>]

Gary, 

This advice is only pertinent to the final figuring stage, as the amount
of "wear" of the lap in this final stage is quite small. 

Besides most of the pitch lost from a lap isn't lost in a manor similar
grinding glass, it's lost through trimming the lap, where the surface
layer remains relatively unchanged, but the material supporting it moves
outward from the centre of each facet/tile. Therefore if there is a
piece of micro grit say 1mm below the surface and 5mm from one edge of
the facet it will move towards the edge of the facet, but it's relative
position to the working surface of the facet will not change much.
Eventually it will reach the edge and be trimmed with the excess pitch.
This is why laps get thinner with use.

Clear skies,
Thomas Janstrom
http://www.tjanstrom.com
http://www.norsewines.com.au
"Your nobody until you've been ignored by your seventh cranio-facial
nerve."


-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf
Of Gary Fuchs
Sent: Wednesday, 8 June 2005 9:45 AM
To: atm@atmlist.net
Subject: Re: [ATM] More Mirror Disasters!


I don't mean any disrespect, but it doesn't sound right to bury 
something that might scratch in the pitch. At some point, if your 
polishing/figuring continues, that contaminant is going to become 
exposed - isn't it? Shouldn't you rather remove the contaminant, or 
remake the lap with clean pitch?

Gary Fuchs



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