Re: ATM Softening pitch

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

Try using the pitch the way it came first.  I've never had to thin any pitch
although there has been some burgundy pitch that I've wanted th thicken a
bit because the stuff was so soft in the warm temps that I was working in.
Ground mirrors can't be tested as they have no flat surfaces to reflect the
light back to the tester.  You need to have a fully polished surface in
order to get the proper reflections.  Any pits in the surface tend to make
strong diffraction edges and the more you have, the worse it is to see what
the surface really is.  You can test the mirror at the 5 micron level to
obtain a rough (within about 1" or so) focal length on the test stand if you
water the mirror surface so that the water surface is the reflecting
surface.
When melting pitch, I use boiling water to do the job.  Pitch will adhere to
a surface while under water so that isn't a problem.  The use of hot water
keeps the pitch from changing its hardness as it doesn't get hot enough to
really exhale the volitile parts.
In addition, rather than going to materials that don't stick to the pitch,
use mold release agents to keep the pitch from adhering to the things you
don't want it to adhere to.  I tend to use hand or dish detergent for a mold
release a lot as it also provides a nice lubricant that is often needed in
the beginning of the polishing process and is easily washed off of the lap
and mirror.  In addition, any vegatable oil does an excellent job of this
chore.  I've even used 10-30W automobile oil for this purpose but don't
recommend that unless you are ready to clean it off of the lap as it seemed
to keep things from starting to work.
For making the grooves in the lap, I tend to prefer the John Dobson method
of a stiff stick that you press into the lap while it is hot if I don't use
a mold (silicone rubber with holes in it) between the lap and the mirror.
I've never tried polishing out a tile tool (curve is the wrong way for a
start) but I'd suspect that the grain of the ceramic will keep a good
surface from being generated.
Hope this answers everything.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net