Re: [ATM] Ball bearing for triangles

[Raphaël GUINAMARD <rguinamard@infonie.fr>]

Hi Mark
In fact I don't know why they are not horizontal... I think the bevel I've made in the triangle is not very well done and not enough symettric to allow the big triangle to be horizontal. See the picture I've sent in the file section.
I've check if the hole I've drilled in the triangle is at the center of gravity of the compete part (triangle+ it's 3 small triangle), and it seems to be approximately correct. So I don't think they are a lot unbalanced
Anyway I agree with you that when I'll have a better bearing, I'll have to equilibrate exactly my triangles by putting some weight at the back of the triangle
What do you mean by "the extra triangle boundary area  for a larger support "?
See also my answer to Tom for the direction  of sperical abberation : the iner apex of the big triangle that needs the highest force to be horizontal is under the others, which could leed to the overcorrection I have on the star test (same shape as the p175 of Suiter's book) 
Thanks a lot for your help
  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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