From: "Tom Krajci" 
To: 
Cc: 
Reply-To: "Tom Krajci" 


From: Rick Maillet 

>Is there a way to finish the assembly with RTV
>silicone holding the mirror and everything in
>place,

See:
http://overton.tamu.edu/aset/krajci/
specifically:
http://overton.tamu.edu/aset/krajci/cell-bearing.htm
and
http://overton.tamu.edu/aset/krajci/cell-12-pt/cross-hinge.htm
...especially the section where Richard Schwartz proposes making compliant
hinges out of RTV silicone.  Easy and inexpensive to make.


>and if so how do you hold the triangles in place

The triangles are glued to the mirror.  The triangles are also glued to the
head of the three collimation bolts.  (You will have to be careful not to
twist the collimation bolts in this case...or come up with another
arrangement that avoids this twisting problem.)

>and still have movement to level out?

You build/glue the cell/mirror...and then install it in the back of the
tube without adjusting the collimation bolts.  Use shims or other
adjustments to get the collimation 'close' and for final collimation you
use the collimation bolts/compliant hinges.  (Compliant hinges work well,
but often don't have a large range of motion...therefore we get
'close' with other adjustments and leave the compliant hinges to handle
only the final/small adjustments.)

>I dont like the
>idea of hold downs, but will use them if I have too.

If you do a clean/well bonding job with the RTV you won't need clips or
other hold downs.

>Next...how much of a vent opening do I need for a fan,
>and any ideas on what type of fan is needed... I hear
>they do not have to draw alot of air, is this so.

Make sure there is room to get air moving around the back of the mirror, as
well as the edges and front.  I don't have an iron rule on fan size. On my
ten inch scope the single fan is about three inches square (12VDC).  On my
16 inch scope I have two, five inch square fans (12VDC).

>Do I also have to make a cap for this venting area? to
>close it off after reaching equalibrium or do you run
>the fan constintly.

In some cases (based on star testing that you will perform, or examination
of the focused image)...running fans all the time is better. In other
temperature/humidity settings...fans are only needed for a brief cooldown
time.  Don't adhere blindly to a certain pattern.  Test and evaluate each
time you observe...and perhaps every hour or so.

I hope this helps,
Tom Krajci
Tashkent, Uzbekistan


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