Re: Test for TDE in grinding
Bob Luffel (bobl@gr.hp.com)
Thu, 9 Mar 95 10:35:05 MST
>
>
> >Subject: Time: 3:38 PM
> >OFFICE MEMO Test for TDE in grinding Date: 3/8/95
>
> >For those concerned about going into polishing with a TDE, here is a simple
> >test. This should be done only with the final abrasive before polishing.
>Clean
> >and dry the mirror and tool. With a waterproof marker, make a tic tac
>toe like
> >pattern on the mirror, going all the way to the edge. Then do a short wet,
> >maybe 30 seconds or a minute with at least a full rotation of mirror and too.
> >Check the wear of the pattern. If it is wearing away gradually all
>around, all
> >is well. If everything is wearing except the edge, you have TDE. If the
>center
> >isn't wearing, the mirror has a hole in the center. Either condition
>should be
> >corrected before proceeding to polishing. This was shown to me as "The Pencil
> >Test", since a pencil works as well as a permanent marker. Hope this is
> >helpful. RICH
>
> Actually, if everything is spherical, then you should not have to rotate
> the mirror.
>
> I would also do the test at the end of a wet, where the abrasive is well
> worn.
>
If you find a TDE, what changes in your stroke should you make to
correct it? I performed this check on my 10" at the 20 micron stage,
and am about to start 9micron grit - the center did appear to wear
faster than the edge. Should this be corrected before going to 9 micron,
or during 9 micron as suggested?
Bob