Secondary Installation Question

Hello fellow ATM types:

I am currently building a 12.5 F6 scope from the ground up. In my design, I will be utilizing a curved vane secondary using a 2.14" diagonal. I am wondering what is the best way to attach it. My thought is to glue it to a piece of dowelling cut at 45 degrees as in Gary Seroniks article. I have read that this will be work but that seems like an awful lot of glass (220 grams) to be hanging off three blobs of silicone.
Can anyone shed some light on how safe this is. I have seen metal panels glued to walls using this same adhesive that 20yrs later pull of large chunks of drywall when trying to remove. I am determined to use this design but I don't want to overlook anything and risk dropping the secondary on the primary (cause then I'd have to kill myself)

Thanks in Advance - Rob Elgert

Be sure to use a fresh tube, otherwise it may not cure properly. I use GE Silicone II, the clear kind, and for secondaries I just buy a new, small tube each time. A couple of times I've removed a secondary that was attached that way, and it was basically necessary to cut through the silicone.

I don't worry, but if you're nervous about it long-term and don't have a mirror box cover, you can store your scope with a drawstring bag made of soft material, pulled up over the secondary and pulled tight around the top of the secondary holder. That, along with not storing the scope vertically, should make the risk of damage very slight.
--
Mike

Rob,
I also have a 12.5" f/6 with a curved spider and have glued the secondary with silicone adhesive. I have rebuilt the spider assembly twice (from curved vanes to wire and back to curved) and from experience the silicone is a bear to remove. My only concern for you would be how the silicone adhesive will adhere to the semi-endgrain of a 45 degree cut dowel (mine is glued to carbon fiber). To be safe I'd sand the cut smooth, apply a thin coat of slow-set epoxy and then lightly sand again when the epoxy cured. This would give a better surface for the silicone to stick to.
Make sure to clean both surfaces with acetone before gluing, to remove any oils that may have come off from your hands. You might also want to glue a piece of string to the back of the secondary mirror and loop it or tie it to the spider (inside of the secondary's shadow) for your own ease of mind. I did this when I first built my scope but on the last rebuild I omitted it when I realized how strong the RTV adhesive really is. Good luck to you.

Doug Tanaka