Re: [ATM] Not tde or tue, important oblate spheroid, ellipsoid

["Arjan te Marvelde" <Arjan.te.Marvelde@hetnet.nl>]

Jerry is probably right.
I have also struggled a lot with erroneous and unpredictable polishing 
behaviour.
It started making sense only after I completely rebuilt my lap.
See http://home.hetnet.nl/~artm/atm/mirror/250f6.html for the notes I kept 
during the 7 years it took.
The last bit is probably the most interesting.

   Arjan


> His lap is his major problem right now. Even if his stroke were "right" by
> either of our definitions he would probably still have the oblate and 
> other
> problems.
>
> In the picture the center facets look thicker and the edge facets appear 
> to
> be thinner than I would use. It looks as if the pitch is channeled all the
> way to the tool. If that is the case I think the lap is too thin. He
> probably needs a new lap but I think I could be wrong about that. It might
> be possible that the lap is thicker than I think and he can trim the
> channels and get the facets more uniform. I'm sure he could make this one
> better, but it might not be good enough.
>
> You have made a couple of good mirrors and I know you went through some of
> the same problems he is experiencing right now. It would help him and you 
> if
> you would tell him how it is you get the good sphere and edge and give him
> some guidance in recognizing the factors that are keeping him from getting 
> a
> good shape. Help him put a good parabola on that glass.
>
> Probably not my place to suggest that, but on the other hand many ATMs
> helped you and it would be a good thing to do likewise. It will make you a
> better ATM if you if you communicate what you know to someone else. You 
> will
> have to think of everything you have done right and everything you have 
> done
> wrong.

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