Re: [ATM] Ball bearing for triangles

[Mark Suchting <masuch@cia.com.au>]

At 06:07 AM 9/2/2004, Raphaël GUINAMARD wrote:

>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.

Raphael,   I think what you are saying is that your triangles don't balance 
because they are thick ( and the extra triangle  boundary area  for a 
larger support pad upsets the balance of the triangle) .  I've seen this 
problem before on a 36" cell with 27 points.  18 point cells don't seem to 
suffer this. Whenever the triangle is strong scalene and you add boundary 
metal they go way out of balance.   300g different  force transmitted as a 
difference in pressure between the inner and outer ring of triangles is 
certainly going to bend your mirror

There is no way around it but to screw lead weights to the back of the 
large triangles until they balance. They are probably tipping in or around 
out and bending your mirror differentially and changing the correction. Are 
the large bottom triangles out of balance  tipping outwards or 
inwards?  Can you correlate this with the spherical abberation direction 
?  ( ie  tipping outwards is going to push the inner triangles up 
and  under correct your mirror).

I don't think roller bearings are going to help the situation , only make 
it worse.

Mark Suchting 
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