[ATM] Snap, crackle, pop, this is the pits

["Chris Dalla Piazza" <dalchri@hotmail.com>]

I am working on the last 9 micron grade of aluminum oxide with my BK7 lenses
and keep on getting one or two pits.  These vary from small specks that
appear dark backlit and grind out after 4 wets to larger ones that are just
big enough to sparkle when backlit.

 

I've tried two different sources for grit and about every other wet, I still
start out with a few grains that are above average.  You can hear them snap
a few times before they are thrown out to the side or grind down.  Sometimes
they are enough to bind and stop the motion of the lenses.  I'm pretty sure
it is the grit because I've tried a few test wets without grit and don't
hear the popping.

 

That said, I finished a Pyrex mirror fine with the same grit so I am
thinking that the BK7 is just soft enough to be sensitive to this problem.

 

I know, a few pits don't mean much, I just want to be really aggressive with
this problem because it will result in 4 optical surfaces with the same
problem.

 

I am trying to mitigate the problem by starting out with a wide circular
stroke to encourage the larger particles to rub themselves out to the sides
of the lenses quickly.

 

I am just curious, anyone else have this problem?  Any suggestions?

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