Fw: [ATM] Ball bearing for triangles

[Raphaël GUINAMARD <rguinamard@infonie.fr>]

----- Original Message ----- 
From: "Raphaël GUINAMARD" <rguinamard@infonie.fr>
To: "A. Suijkerbuijk" <a.suykerbuyk@wxs.nl>
Sent: Sunday, September 05, 2004 4:44 PM
Subject: Re: [ATM] Ball bearing for triangles


> Hi Adrie
> No the mirror has a classical one face aluminated.
> The aluminated face has a lower temp because it sees the space which has a
> 3K temperature.
> The other face sees the ground and its 270-300K temperature.
> The gradient of temperature of the 2 faces cause spherical aberation. In
the
> example of the 1.5 m mirror with a 28 mm  thick mirror (meniscus) the
> difference of temp is about 0.8° and cause a very big (10 wave !)
spherical
> aberation
> So what they've done is to heat the aluminated face whith a courant to
heat
> the upper face and suppress the sperical abberation.
> To heat in a very constant way, they've put 40 groups of electrodes.
> What could also be done (maybe more easy) is to heat the upper face with a
> infrared laser...
> ----- Original Message ----- 
> From: "A. Suijkerbuijk" <a.suykerbuyk@wxs.nl>
> To: "Raphaël GUINAMARD" <rguinamard@infonie.fr>; "ATM Group"
> <ATM@atmlist.net>
> Sent: Thursday, September 02, 2004 8:16 PM
> Subject: Re: [ATM] Ball bearing for triangles
>
>
> > Bonjour Rafael,
> >
> > You could drill holes in the triangles to restore the original centers
of
> > gravity. However I wonder if stainless steel is the best material for
> > bearings. This stuff "freezes" easily. Bolts and nuts out of stainless
> steel
> > need much play and even then you can have problems.Perhaps the use of
> > aluminum would be better.
> > Interesting to read about "heating the aluminum layers". I understand
that
> > in this case both sides of the mirror have a aluminum coating? Normally
> the
> > back side of the mirror cools most, since the aluminum avoids radiation.
> >
> > Regards,
> > Adrie Suijkerbuijk
> > ----- Original Message ----- 
> > From: "Raphaël GUINAMARD" <rguinamard@infonie.fr>
> > To: "ATM Group" <ATM@atmlist.net>
> > Sent: Wednesday, September 01, 2004 10:07 PM
> > Subject: [ATM] Ball bearing for triangles
> >
> >
> > > First of all, I apologie for my poor technical english...
> > >
> > > I have a 24" f/3.3 dob.
> > > My mirror is very fine (40mm) an I have built a 27 point mirror cell
(9
> > > small triangles on 3 big triangles).
> > > For the "rotation" of the big triangles I have used a carriage bolt
that
> I
> > > have drilled so that the collimation bolt could pass though, and I
have
> > > beveled the bottom part of my triangle so that the spherical part of
the
> > > bolt could fit in it.
> > > I have put only a very very small amount of grease.
> > > My big triangles are quite heavy (6 mm stainless steel) and my problem
> is
> > > that there is friction and my triangles needs each approx 300 g of
> force
> > to
> > > be really in the same plane.
> > > I think this could deform a little bit my miror because I see some
> > spherical
> > > aberration in the star test.
> > > My question : does anyone has example of using bearing to support the
> big
> > > triangle (close picture, reference where I could find the bearings) ?
> > > I've seen Bruce Sayre page
> > > (http://www.foothill.net/~sayre/22-in.%20binocular.htm) but I can't
get
> in
> > > touch with him to have more details .
> > > Thanks for your help
> > >
> > > _______________________________________________
> > > ATM mailing list http://www.atmlist.net/
> > >
> >
> >
>

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