[ATM] Re: Ball bearing for triangles

["lou krajci" <loukrajci@comcast.net>]

>From: Rapha?l GUINAMARD <rguinamard@infonie.fr>

>>the edge supports are somewhere in the middle of their
>> allowable range of flexure?...

>I don't understand exactly your questions.

Your edge supports have a middle/central/neutral/zero stress position.
Ideally, you'd like to install your mirror so that when the edge supports
support the mirror...they are in this neutral position.  You don't want them
in a strongly bent/stressed state...their purpose is to provide lateral
support...which is force along the longitudinal axis of the edge support.
If they are in a bent/stressed state, then they are also putting sideways
forces on the mirror, which is not what we want.

>>how do you tell if the mirror has pushed the
>> edge supports beyond their useful limit of flexure?

>In fact, at the end of the laser collimation, and before the star test
>"ultimate" collimation I have to move (just a little bit) the piano wire to
>get rid of constraints. Otherwise I have a big amount of astigmatism due to
>the piano wire.

This sounds reasonable to me.  It seems you are making sure the edge
supports are in a neutral position.

>In fact I'm not so happy of this piano wire because even when I move a
>little
>bit the piano wire, it's difficult to get rid of the astigmatism and I have
>to move several time the piano wire.

Maybe you just need to modify the edge supports so that they can be easily
shifted in precise amounts?

>I think I'm going to upgrate on a
>different lateral
>support like this one : a caster (don't know if it's the correct
translation
>for the french "roulette") lateral support:
>on a 32" with astatic cell :
>http://www.atmlist.net/contrib/rguinamard-at-infonie-dot-fr/600f3.3/MyFutur
eLateralSupport%3f%3f%3f/globalDevant.JPG
>detail :
>http://www.atmlist.net/contrib/rguinamard-at-infonie-dot-fr/600f3.3/MyFutur
eLateralSupport%3f%3f%3f/RouletteCeinture.JPG

Yes, caster is a decent translation.  Yes, this approach allows the edge
support to avoid producing stress in the front/back (sideways with respect
to mirror's edge) direction...which is a good thing.  I've also heard one
ATM mention using a chain of beads...a series of many small casters.

This caster idea also shows promise.

Tom Krajci
Albuquerque


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