[ATM] PVC pipe, Aluminum Hydroxide, and rough mirrors

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

For cutting PVC pipe, the "wrap the long piece of paper around the
tube" method really does work very well for marking it for a square 
cut.  Unless one has an improbably large (and accurate) cutoff saw 
available, cutting by hand is the simplest way, since PVC is soft and 
cuts quite quickly and straight with a good quality crosscut saw 
(intended for making good cuts on wood).  This is the type of saw that 
few use anymore since they prefer power tools.

Francis J. O'Reilly wrote:
> Aluminum Hydroxide is in granular form and can be purchased from 
> Ace Hardware stores. It doesn't take much to clean the mirror, use 
> a fairly dilute mixture, try a tablespoon per quart to start. The 
> hardware store may not admit to having Aluminum hydroxide, but they
> generally do. You can find it on the shelves by the commercial 
> drain cleaners.

Nooooooooooooooooooooooooooooo!
If you care about optical smoothness, stay away from caustics.  Far, 
far away.

Stick with ferric chloride for coating stripping, or green river 
solution.  Alternatively, clean the mirror thoroughly to remove all 
dirt and then polish the rest of the coating off.

I use the plastic scrubber method quite regularly to remove cerium 
around the edge of the mirror and I've never scratched a mirror doing 
that.  Just take care.

Dale Eason wrote:
> http://home.comcast.net/~doeason/Surface_images.pdf 1meg file.
> This mirror has a surface similar to one that Texereau shows in his
> book where he states it was caused by too much pressure and too
> fast a stroke by an over enthusiastic mirror maker.
> This is about the worst surface I have ever measured. I am using
> the PDF file format because there is a lot of detail in these
> images and one can zoom in and out of them easily in that format.
> I show real ronchi and Foucault images and compare them to the 
> interferometric data.
> Would anyone care to speculate on the cause of this surface?  The
> mirror is an 8 molded Pyrex blank.  The the words "Pyrex made in
> the USA"  and "8D" molded into the back.  The sides are slightly
> tapered to allow it to be removed from the mold. It was once 
> aluminum coated but nearly all of it has gone.

This reminds me a bit of a 5.25" mirror that was given to me.  It was 
in an old telescope, and when I pulled out the mirror cell there was a 
mouse skeleton on the mirror!  Not knowing much about mirror making at 
the time, I sent the mirror in for recoating and put it in a scope. 
It performed terribly.  That mirror was packed away and other scopes 
were built.  Eventually I got into mirror making and several years ago 
I set the 5.25" up for testing and saw a horribly rough surface 
superimposed on what looked like a smooth parabola in the background. 
  I didn't get any photos, and the mirror has since been refigured.

	Mike Lockwood

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