Re: [ATM] Ain't got no shperometer

[Peter De Baan <pdebaan@hotmail.com>]

Better yet, do not store two same size mirrors next to each other.


Peter

> Date: Tue, 27 Nov 2007 22:09:37 -0500
> From: wa4guu@verizon.net
> To: atm@atmlist.net
> Subject: Re: [ATM] Ain't got no shperometer
>
> Norm has it quite right.
>
> It is learn by doing. All the advice is to help you recognize the experience
> when you encounter it.
>
> Look at it, feel it. Whether it works out good or bad remember it. Recognize
> the differences between what worked and what didn't.
>
> The Sharpie test is not the only way to know the surface shape. I don't use
> the Sharpie test, but I think it is a good method for someone who has not
> yet learned how to see and feel the proper shape and maybe hasn't settled
> into a normal stroke that will produce the correct shape.
>
> With a full size tool, if you do what is widely considered the "normal
> stroke", a W 1/3D high and 1/4D wide you will end up with a sufficiently
> spherical shape.
>
> If that is true, when would you use the Sharpie test? That would be after
> you have used a large overhang stroke to change the radius of the mirror,
> and you have used the "normal stroke" for a while to spread the curve
> smoothly from center to edge.
>
> After hogging in rough grinding would be one time you would work to make
> them spherical again. And then if you shoot for a target ROC you might at
> any or all stages of fine grinding try to force the ROC to the target with a
> large overhang, either MOT or TOT. So again you will want to smooth the
> curve from center to edge after altering the sagitta with the large
> overhang. It will always be a hole in the middle that you are trying to
> spread evenly to the edge. So you might use the Sharpie test to see if you
> have done a good job of smoothing the curve.
>
> If you had it spherical with the previous grit and you have only used
> "normal" strokes, by the time you have the pits worked out with the present
> grade of grit, there is no reason that it would not be a sufficiently
> spherical surface.
>
> Well I see Pete has posted again.... And that brings me to another time you
> might do the Sharpie test. That would be after you have put the wrong tool
> on the mirror and you have been trying to mate the curves of the proper tool
> and mirror. In this case the Sharpie test may be superior to seeing and
> feeling if you did not change grit grades during or after your mistake. The
> surface could have the same pit sizes from center to edge and it could feel
> smooth while working if the central area is large enough.
>
> Do it like Ken says. He invented it, he can't be wrong about how to do it.
>
> Color code the mirrors and laps so that mistake doesn't happen again.
>
> Jerry
>
>
>
> -----Original Message-----
> From: Norm Prince
>
> Look at the glass...are the pits even?...is the outer portion getting even
> pits before the inner or vice versa?....If you are alternating tot and mot
> with more or less randomly even intervals then it should be as close as you
> are likely to get if you don't have someone who has done it to give you a
> direct second opinion...Does it feel like the action of surface on surface
> is smooth?...
>
> you seem to know enough about what you are trying to do to have actually
> tried it so keep going and you will soon find out what you have and haven't
> quite done...of course take whatever bits of advise you find on list they
> are groovey dudes and know infinitely more then me...
>
> but from one inexperienced cat to another...without that hands on "here you
> look at it"...kind of back and forth with someone who has tried it too, we
> are working on a learn by doing basis...so go with your gut and see what
> happens...
>
> -Norm Prince
>
>
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/

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