Re: [ATM] 20" *glass* tool

[asw45 <asw45@student.canterbury.ac.nz>]

Hi Bob,

Thanks for your reply. The barbel does have a 1" or so ring around the 
outside. It has a central ring also but that doesn't appear to have been 
touched much when grinding the previous mirror.

I know a guy who is currently modifying a few hundred CCD chips (apparently a 
super delicate job with a special soldering iron, but I don't know the 
details) for building cameras with. I'm not that familiar with the various CCD 
cameras out there yet other than the basic principles of operation.

Is pouring the plaster over the tiles superior to pouring the plaster directly 
onto the mirror, sealing the tool, and then attaching the tiles using epoxy or 
wax? My tiles are very thin only about 4mm thick and I'm fairly sure I'll have 
to replace them at least once.

Does float glass need the back ground flat as is recommended so strongly for 
thin mirrors? If so, is the other piece of glass a good tool for this? What 
stroke is used?

Cheers
Alan




>===== Original Message From Bob May <bobmay@nethere.com> =====
>The barbell weight wants to be one of those that have the rim
>ridge rather than the ellipticaly shaped ones (looking at it from
>the edge) as you don't need the grinding in the middle of the
>weight so much as at the edges where the ROC changes in the glass
>doesn't lift the working surface off of the glass.
>As to the Hydrocal and other such pourable stones, it really
>doesn't matter which you use as the basic function is to provide
>a waterproof pourable stone to hold the ceramic tiles which
>actually do the work of grinding.  Plaster of Paris isn't a
>waterproof stone so it doesn't qualify for the making of the tool
>unless you seal it from the water and then epoxy on tiles
>afterword which makes the whole process of making a tool way to
>compled.  I just put a dam around the mirror, put some tiles on
>the surface and then pour the stone in the hole.  I am usually
>starting my grinding about 1/2 hour after I start mixing the
>stone even tho the stone isn't fully setup and rock hard all
>over.  Make your tool after you hve the basic hole in the glass
>and everything will work fine.  Leave the steel and glass for
>other projects.
>Longer FL scopes are nice but remember that at F5, the scope will
>be at least 8' tall which means you're going to need a ladder to
>access the EP anywhere near the straight up direction. so beware!
>The Cookbook camera is now obselete as the sensor chips are no
>longer being made so something more like the Audine camera is
>what you are going to build if you build one.
>Bob May
>bobmay at nethere.com
>http: slash /nav.to slash bobmay
>http: slash /bobmay dot astronomy.net
>Addresses have been munged up to keep spammers from bothering me.
>replace the obvious words with the proper character.
>Thank you for your understanding!
>
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