Re: [ATM] The mouse in the mirror

["Shane LaPierre" <shane@ct-astronomer.com>]

Squeak is good earlier, but probably not during figuring.

Best luck,
Shane

On Tue, 04 Dec 2007 10:12:43 -0500 ArtfulBodger 
<artfulbodger@earthlink.net> wrote:

> Thanks, folks, those of you who helped me with 
>spherometer/sharpie 
> issues.  The sharpie showed me what I didn't want to 
>see, and it took 
> considerable grinding to get things spherical; but now 
>the sharpie is 
> happy and the grinding's done.
> 
> So, polishing.  I'm using a cerium/water slurry, pitch 
>lap, pyrex 
> blank.  (Two laps, actually, on two mirrors, one 8" 
>f/4.5, one 8" 
> f/5.5.)
> 
> Now, I know guys who seem to use a fair bit of the 
>cerium gravy, they 
> keep everyting pretty wet.  Use enough so that the 
>mirror slides well 
> on the pitch.  Also they mix the cerium and water 
>somewhat on the 
> thick side.  I can't tell you the actual proportions 
>they use, the 
> mixture just seems a bit rich to me.
> 
> I tend to keep the mix thinner and use less of it: I 
>want the mirror 
> to be a fairly hard push -- but smooth, not grabby! -- 
>across the 
> lap.  It seems to me that that's when the cerium is 
>doing its work: 
> not when the mirror is skidding over the lap, but when 
>it's pushing 
> across it, hard and slow.  Fairly hard and slow.  Not 
>from weight on 
> the mirror, not pressure on top, but friction on the 
>surface.  I 
> don't let the lap get dry, but I use as little gravy as 
>I can.
> 
> I don't know if this is good or not.  It seems so.
> 
> And when the push is slow and smooth, and the lap is not 
>Not NOT 
> dried out, and the mirror starts to chirp like a bird or 
>squeak like 
> a mouse -- is that an evil thing?  Does it just mean 
>good friction 
> and a good fit between mirror and pitch?  Or does it 
>mean I'm 
> polishing a chirpy, wavy surface texture into the 
>mirror?
> 
> Or what?
> 
> I've read some guys (websites) who mention the squeak in 
>passing, as 
> if it were normal; but I dunno.  Could just add more 
>gravy, but I'm 
> not so sure about that, either.
> 
> So.  The squeak.  Evil noise and cry of pyrex pain?  Or 
>sign that the 
> lap is working good and hard?
> 
> Pete
> 
> -- 
> Artful Bodger
> http://www.artfulbodger.net
> _______________________________________________
> ATM mailing list http://www.atmlist.net/

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