Re: [ATM] Spherometers and sphericity

["Norm Prince" <princenorman@bellsouth.net>]

Just curious...why "slide" the thing around?...can you not pick it up and 
gently place it somewhere else...then take a reading?...You still find out 
what you want to know w/o pushing steel things around on your pretty, and 
softer, glass surface.

-Norm Prince


----- Original Message ----- 
From: "Mike Lockwood" <melockwo@uiuc.edu>
To: <atm@atmlist.net>
Sent: Wednesday, November 28, 2007 11:40 AM
Subject: Re: [ATM] Spherometers and sphericity


> Ken,
>
> Sorry I hijacked the sharpie test, Ken.  I'll refer to what I do as
> the "sharpie even wear test".
>
> kreig wrote:
>> A sphereometer is used to determine the radius of curvature, only. 
>> Dragging
>> a sphereometer around on ground glass is a sin and will quickly wear the
>> contact points making the sphereometer inaccurate.
>
> Then I guess I'm a sinner, according to your gospel.  It's more of a
> gentle sliding action rather than dragging.
>
> If one uses a quality indicator and zeros it before every use (on a
> decent optical flat), then any wear is automatically calibrated out
> and has no effect on the measurement.  To get precision to 0.00005"
> (that's a little over two waves) I need to zero it immediately before
> I use it anyway, because temperature and other subtle variables affect
> the measurement.
>
> If I ever wear down the 1/4" ball bearing feet of my spherometer
> basess, then I will simply knock them loose and glue on new ones.
>
> If your mirror and spherometer are clean and you have rounded contact
> points on each (bearings, rounded indicator tip), then you won't get
> any scratches, either.  I have pushed a spherometer around on plenty
> of 5u-ground surfaces and I have never gotten a scratch.
>
> I am done preaching, but I will keep "sinning".  :)
>
> Mike Lockwood
>
>
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> 


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