Re: ATM OK OK glass IS a solid just like my...

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

Lots of questions!
As to the grating, it needs to be square with the mirror to a fair degree
otherwise it will be indicating things that aren't true.  I've got a
handheld design on my website for a reference to what's going on if you want
to look at it.
As to a Foucault tester, you'd be supprised at how rough a tester can look
and still work well.  I've built them from scrap lumber, etc. and the most
important thing is that the KE smoothly move across the light's return and
that you can measure the travel in the mirror's direction by .001" or so.
The mistake a lot of people have made (I made it with my first tester) is
that you need to know where the KE is in crosstravel.  The other thing is
that people often fail to get the motions to be smooth.  When you can get
the crosstravel movement to the point where you can smoothly control the
brightness of the image then you are there.
As to other parts of the tester, I'd suggest that you find a security camera
or even use a small camcorder and have it sit behind the KE so that you
don't have to get your face down there.  The lens needs to be right behind
the KE and is focused on the mirror, not the KE (remember that your eye is
looking at the mirror, the camera operates just like your eye!).  This will
also mean that you may want to put together a finder LED for the tester
which is nothing more than a very bright LED which, when reflected back,
goes to a spot predetermined to put the KE LED into the middle of the lens
when you turn that LED on.  Also, you will want to be able to control the KE
LED's brightness so that you can set it at the point where the camera starts
to control the brightness of the incoming light - get too much light in and
the camera will start causing problems with the image.
For the Pitch Lap, the Dobson method is quite delightful and I'm doing it
about as fast as his method with mine.
Dobson heats the pitch up in a bucket and then pours it over the tool and
puts the well CeO, water and detergent mix coated mirror on top until it
cools a bit.  He then presses into the lap with a stick the grooves desired
and then presses some more.  Eventually, the lap is formed by this method as
the pitch cools.
Mine is a bit different as I put some pitch pieces on top of the lap and
throw the lap into the microwave and slowly microwave the whole mess until
the pitch starts moving.  At this time, there is usually enough heat in the
tile tool to finish the heating and I just turn the pitch over once or twice
to insure that it's all flowing and then grab a silicone rubber mold (sheet
silicone with a bunch of round holes in it in a triangular pattern to
maximize the amount of hole area), slobber it up with the aformentioned CeO
mix and put it on top of the pitch and then put the mirror on top of that,
also slobbered good.  Let cool and make sure that the pitch is in contact
and you have a lap that works well.
I've been running the San Diego AA mirrormaking group for some time now and
these are some of the processes that we've been doing and the processes are
all fairly easy to do.

Bob May
http://nav.to/bobmay
bobmay@nethere.com