Re: [ATM] my ongoing war story (polishing and figuring)

["Rodney Mayes" <rgmayes@bellsouth.net>]

----- Original Message ----- 
From: "Mike Lockwood" <melockwo@uiuc.edu>
To: <atm@atmlist.net>
Cc: "Rodney Mayes" <rgmayes@bellsouth.net>
Sent: Wednesday, February 15, 2006 10:11 AM
Subject: Re: [ATM] my ongoing war story (polishing and figuring)


> Rodney,
>
> I don't think you mentioned the size, focal ratio, thickness, and 
> substrate type (Pyrex, plate glass, etc.) for your mirror.  That is info 
> you should share.


My apologies.  It was late when I posted.

10 inch diameter
f/7.55
7/8 inch plate glass
>

> Rodney Mayes wrote:
>> I would appreciate any good advice that any of you good folks would
>> care to offer on the figuring process.  I am using a full sized lap
>> that is beveled just enough to make the lap about 1/10 inch smaller
>> diameter than the mirror.
>
> You might consider using a larger bevel (1/8" - 3/16").  If any lap facet 
> hangs over the edge while pressing (due to decentering), the resulting 
> unpressed facet will turn the edge in a hurry.

Agreed.  I have been very cautious of this.

>
>> Since this is my first try, I am a
>> little unsure of the parabolising stroke length, amount of
>> pressure, stroke speed, how much to turn while stroking, etc.  I
>> just try to be random, follow the info that I have available, and
>> learn as I go.
>> Anyone know of any videos available that details the figuring
>> process?
>
> Here's a link to my figuring page:
> http://bi-staff.beckman.uiuc.edu/~melockwo/mirror_making/full_lap/full_lap.html
>

Thank you.  I will definately check it out!



> I can't comment on the central hill because we don't know the cause yet. 
> But I will say that the corrections for the outer zones are far more 
> important at this point.  With proper technique, a central hill can be 
> removed in minutes and is far less worrisome than a rolled outer zone or 
> severely undercorrected outer zone.

Since I began the project, I have been very, very, cautious with regards to 
the edge (TDE).  So much so, that I have ended up with a TUE that caused me 
to have to polish a lot longer because I did not want to return to fine 
grinding if at all possible.  The edges look good as far as I can tell. 
Ronchi bands look good and I have not, at least visually, noticed any edge 
problems. Best regards.
>
> Some zonal Foucault readings, the radii of your zones, the ROC of the 
> mirror, and its size will be useful info in your next post.  That will 
> give us a better idea of what's going on.
>
> Mike Lockwood
> 

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