[ATM] The 15.5 Ultrathin Project, some lap notes

[vorblesnak@peak.org]

I stripped the old 12 inch lap, and melted the pitch with some new stuff. 
I poured this onto a piece of paper and faceted it so I could break out
squares of pitch.  No pictures, sorry.  I took the grinding tool and using
a torch and an old chisel, I stripped the glass squares and epoxy off. 
Now I cleaned the took well and then drizzled very hot pirtch onto the
tool and pressed the squares on, gluing them into place with the hot
pitch.  Here is a picture of the raw tool and lap after I was done ..

http://www.atmlist.net/contrib/vorblesnak-at-peak-dot-org/15.5%20Lap/New%20and%20Chunky.jpg

Now to tuning the lap.  I got out an my wash tub and filled the bottom
with about 6 inches of hot water from the tap.  Three spacers on the
batton and set the tool / lap on the spacers, submerging the lap in the
hot water.  The spacers, old jar lids, are there so I can get my fingers
under the tool and lift it out.  I checked the pitch for softness every
now and then and when it was soft I pulled it out and pressed it with the
mirror to shape it.  I prepped the mirror with soap the first press as I
knew it would go back into the water at least a couple of more times.  The
last press and tuning was done with cerium oxide on the mirror to charge
the lap.  Here is apicture of the lap in the "tuner" ...

http://www.atmlist.net/contrib/vorblesnak-at-peak-dot-org/15.5%20Lap/Tuning%20the%20Lap.jpg

Finally, a tuned lap.  Good contact, good drag while polishing.  I am
concerned about glass flex while polishing so I am using a 20 pound ring
weight to press the glass to the pitch while I polish.  I just move it
back and forth on the lap.  I suspect this will take longer to polish out
but hopefully  I will not induce any astigmatism.  Another possible source
of astigmatism could be the heat of my hands on the glass.  I move the
glass with the ring weight and it is resting on a piece of foam shelf
liner, so hopefully I am not inducing any odd shaped heat zones into the
glass.  Thin stuff.  Here is a picture of the tuned lap with some cerium
on it ..

http://www.atmlist.net/contrib/vorblesnak-at-peak-dot-org/15.5%20Lap/Tuned%20and%20Frosty.jpg

I will try and get a picture of the glass on the lap with the ring weight
on it.  Also, I have not forgotten my promise of some ronchi pictures.

David Davis
Toledo, OR 97391

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