[ATM] The ultrathin projects

[vorblesnak@peak.org]

It is quite nice to have been absolutely swamped and suddenly find myself
with some clear time.  Yesterday I laid out the garden, hauled garbage,
patched the wood pecker damage and then found enough time to cast a tool
for the full size lap for the ultrathin glass.

I put a duct tape dam around the perimeter of the 15.5 and mixed up some
RapidSet concrete patch.  It dries hard and finished in one hour.  I
poured in about half of the mix and then laid a piece of 1/2 inch hardware
cloth on the surface, then poured in the rest of the mix.  The resulting
tool is about one inch thick and perfectly smooth on the top.

Today I melted all the odd remnants of pitch I had around the place.  I
blended in about 1/3 of a cup of turpentine, about 100ml, to soften the
pitch.  I did a drop test into cold water to test the hardness and found I
had a pitch that I could press channels into while cold.  That is mighty
soft,  but it is what I wanted.  I can press in the channels and then let
the weight of the mirror bring the surface into contact.  I will probably
only get a few minutes of polishing time before the channels close, but
hopefully the glass will not be warped by pressure.

Here is a link to some pictures of the process...

http://www.atmlist.net/contrib/vorblesnak-at-peak-dot-org/Full%20Size%20Tool/

I will start with the 15.5.  It is mounted to a backboard with silicone
RTV rubber.  The backboard it 3/4 inch thick medium density partical
board.  I will leave the glass on the board and work it that way.

I will work the 16 inch by hand while wearing gloves.  This will test if
that much insulation is enough to prevent the glass expanding from the
heat of my hands.

The pie plates will be finished on a small polishing machine I built.  All
will be worked with full size tools, very soft pitch

The weather is cool and rainy, perfect for this type of pitch.  I suspect
there is a few hours of polishing to bring the surface of the glass into
figure.  I will post more as I have news to offer.

David Davis
Toledo, OR 97391


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