Re: [ATM] First Pitch Lap - any tips?

["Bob May" <bobmay@nethere.com>]

First and formost tip - don't worry too much about the shape of the lap.  If
you are getting the blocks all touching the mirror, you are fine, even if
only 1/2 of the block is touching.  Even if the lap is only 90% of the
diameter of the mirror and is oddly shaped.  If the pitch is soft enough, it
will quickly make a very nice lap.  Big bubbles in the blocks are just fine
as these also end up as little resovoirs of CeO for the polishing action.
Next, the lap should always give a very viscous feel to the contact between
the lap and the mirror.  If you can slide the mirror over the lap with
little force, nothing is happening to polish the mirror. Slip and grab is
usually an indication that the lap and mirror aren't in good compliance with
each other and a bit of warming of the lap should cure that quickly.
I'll use a pan of hot water to do a flash heat of the surface of the lap
(only a few seconds of the lap surface in the water)  to bring that last
little bit of shape to a lap while a longer dip will get the heat deeper and
take care of bigger problems with surface contact.
A drop of detergent into the CeO/water mixture will help with making the
water from really evaporating and locking the lap and mirror together.
Hair netting or other fine (3/8" to 1/16" netting) will do a good job of
microfacetting the surface of the lap after it is basically in the proper
shape.  Do make sure that you don't let the pitch get too far into the
netting or you will have problems pulling it off.  Better to have to warm
the lap again to get the tops of the microfacets in contact.
Do try to get the appearance of the lap even - if you microfacet, the whole
surface should be microfacetted otherwise the action will change in
different regions.
Finally, if you are unsure of whether the lap is good, try it and see what
it does!  For initial polishing, anything that scrapes the mirror will help
along the way as you will get the surface polished and as you work, the lap
will start to look better to you as more of it will become into compliance
with the surface of the mirror as the blocks gradually sink.  Spend your
time futzing with the mirror on the lap pushing the lap into compliance at
the first part of the polishing rather than the lap itself and you will be a
lot happier.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net


_______________________________________________
ATM mailing list http://www.atmlist.net/