Re: ATM concentric hills

["Bill T." <twentiethwave@hotmail.com>]

Ryan Hess wrote:
> As a general comment, 1/4 COC TOT stroke will **kill** any TDE that your
> mirror has.  However, after an hour of this, my mirror has taken on some
> "concentric hills".  They look like they are caused by the lap, (which the
> squares are off-centered), so I should probably focus on that.  Does
anyone
> know how to get rid of this problem?  (Besided making a new lap?)  I ran
out
> of pitch, and this one is getting thin (1/7"?)  Any ideas?  Thanks,

Probably your strokes were too regular.  Does do the hill spacing correspond
to the channel spacing on your lap?  Did you rotate the tool?

One cure might be to spend some time on classic W polishing strokes,
alternating mirror and tool on top.  This stroke has the advantage of
averaging out lap induced artifacts over a wide area.

1/7" is getting pretty thin.  Unless you're close to figured, it's time for
retread.  As it thins down it will start to act like an overly hard, badly
pressed lap.  You can very temporarily gain some extra thickness by
channeling, if you're now un-channeled.

It's true -- COC, TOT can often cure a TDE.  I've even turned edges from
down to UP that way.  Go easy!  Check often!  But unless you include at
least some side to side you can also get a vicious zone just in from the
edge...and other concentric artifacts.

Bill T.