RE: ATM - Chips on Tool

["Meeks, Robert" <RFMeeks@epicsolutions.com>]

Hi Richard,

Thanks for all of the helpful information.  I'm cool with the sharpie test,
sun test, etc. but I have not encountered what you listed as "redout" test.
I searched the archive for "redout" but there are no entries.

If you have a chance, could you elaborate on that one a bit?

Thanks again,
Bob

> -----Original Message-----
> From: Richard Schwartz [SMTP:richas@IDT.NET]
> Sent: Tuesday, January 05, 1999 10:16 AM
> To:   RFMeeks@epicsolutions.com
> Subject:      ATM - Chips on Tool
> 
> The chips on the edge of your tool are not a problem until you get into
> fine grinding.  At that time, a chip coming loose will scratch the heck
> out of your mirror.
> 
> You should keep the mirror and the tool beveled.   How much bevel?
> Just enough so that it does not feel sharp when you run your thumb over
> the edge.   A bevel of 1/32" is overkill.
> 
> Since you are using a glass tool, I want to advise you that you will do
> much better in fine grinding if you cut channels into the tool.   Make
> six channels in the pattern of a four-by-four tic-tac-toe.  To cut the
> channels, use the edge of a whet stone tilted 45 degrees.  Work by hand
> under running water or in a bucket.   Channels 1 mm deep and 2 mm wide
> are fine.
> 
> The channels improve fine grinding, especially out at the edge of the
> mirror, by allowing the grit slurry to flow around to all areas.   But
> don't cut those channels until you have the curve hogged out and you are
> ready to go to #220 grit.
> 
> While you are learning to grind, you should also learn to work on a
> Dobson workbench.   It is a plank across two 5-gallon buckets.   You
> work seated, which is more comfortable than standing for long periods.
> At the end of each session, you nest the buckets, put the plank in the
> buckets, and put the whole thing away in the closet.   All parts of this
> workbench have other uses when the project is done.   The only downside
> is that you cannot "walk around the barrel".   No big deal; just rotate
> the bottom workpiece periodically.
> 
> You should also learn to do the sharpie test for quality of contact
> between the mirror and tool, the sun and flashlight tests for focal
> length, and the redout test for quality of the surface during fine
> grinding.  If you have any questions about these tests, just ask.
> 
> . . . Richard