RE: ATM Re: Collimation problems

[BOB PRABOWO <BOB@bahana.co.id>]

Hi Luis,

>As I marked the center of the mirror I have noted that If I collimate
>in
>        vertical position, when I tilt the tube under 60 deg. the
mirror is decentered                          and viceversa
>I think on three causes:

>1.- The mirror is displaced because the silicone is not rigid.
To avoid sideways movement maybe you should use edge supports/side
suports.
Use three dowels, placed them 120 degree apart at the edge of the
mirror. There should be a clearance between the mirror and the dowels,
about 1/4". You then fill the clearance with silicone blop.
Here's how it looks like:

                  mirror                                o= silicone blop        

        ---------------------------------    
                            !o I  I      
        -------------------oo- ---------!o I  I  dowel/edge support
    ----------------------oo--------------I  I----
   !------------------------------------------------! mirror cell


>2.- The mirror cell is displaced because the springs don't make enough
>pressure.
For my mirror cell, the collimation bolts also use springs. And to
attach the bolts to the mirror cell I drilled three holes on the cell
and place t-nuts in the holes. The collimation bolts then screwed in to
the three t-nuts. This, I believe, will prevent the collimation bolts
from moving sideway.

>3.- The sonotube bends under his own weight (most probably).
Then you should reinforce the tube, using fiberglass for instance. Check
the archives there were threads on this subject before.