RE: [ATM] Ball bearing for triangles

["Peter" <peter@kitgear.com>]

Hi Adrie,

Please explain what you mean about stainless freezes easily?? Stainless has
1/2 the thermal expansion coeff of aluminum.

Thanks,

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net]On Behalf
Of A. Suijkerbuijk
Sent: Thursday, September 02, 2004 2:17 PM
To: Raphaël GUINAMARD; ATM Group
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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