From: "Mike and Sara" 
To: 
Reply-To: "Mike and Sara" 


Hello!  I am trying to decide whether to glue my F3 12.5 inch primary to my
9 point mirror cell or not.  I've created a little different cell.  Instead
of having the collimation bolts go to each triangle, I have each triangle
bolted to an underling board, and then that board attached to another board
with the classic bolt/spring arrangement.  As a result, with collimation,
the distance between the triangles will not change - the entire mirror
plane will shift.

    In such an arrangement, I thought I could glue one point of each three
point triangle to the mirror, and allow the other two points of each
triangle to float freely.  This would eliminate the problem of differential
flexure between the mirror and polymer glue compound.

    However, I am concerned about how accurately centered the mirror must
be.  I have read in the archives that the mirror must be centered to 1/16
inch or better with respect to the secondary in order to achieve maximum
performance for the system.  If this is the case, then having a support
system that would allow the mirror position to be varied, such as the two
wire scheme I have seen presented in the archives, makes sense as opposed
to fixing the mirror to the mirror cell.

    If, on the other hand, if I can glue the mirror to the mirror cell
support, it would make the system much more convenient to use.

    What are people's opinions regarding accuracy of centering a primary?
Thanks and best regards.

Mike Heald

--- BBBS/NT v4.01 Flag-5