Re: [ATM] Secondary cowl

[Mike Lockwood <melockwo@uiuc.edu>]

Michael,

Michael Lindner wrote:
> I'd like to make my own spider/secondary holder, but I am faced with 2 
> posisbilities:
> 1. silicone the secondary to the holder. This would require a holder that is a 
> bit thicker (and therefore heavier) than I wanted. Also, although I've 
> siliconed secondaries in the past without mishap, I'd still feel better with 
> it held all around the edge...

It works, but I understand your reluctance.

> 2. Find a metal "cowl" that's the right size to hold the secondary. 
> Unfortunately I know of no source for this, other than buying a secondary 
> holder than throwing most of it away.

Make your own.  It's some simple sheet metal work.

Find a plastic pipe or wood dowel - something round and about the same 
diameter as your secondary's minor axis.  This will be the "form". 
The form can be made slightly larger with a few careful turns of tape.

Roll some thin sheet aluminum (available at a good hardware store) 
around one end of it and cut it so that it goes around the "form" 
exactly once, with a nice seam.  Tape/screw it securely to the form. 
(I can measure the thickness of the aluminum I used if you need it, 
but I'm guessing it's 0.020" thick.)

If you have a mitre saw with a carbide blade, you can quickly chop off 
the end of the pipe and aluminum at a 45-degree angle.  Just make sure 
everything is securely clamped.  Lacking this, cut the round item at 
an accurate 45-degree first and then trim the aluminum with a hacksaw 
to match.  Sand/deburr the edges of the cut aluminum so there are no 
sharp spots to scratch your secondary.

Slide the aluminum about 1/16" or 3/32" towards the cut end and then 
lightly hammer the overhang over into a lip to retain the secondary. 
Hammer a little at a time, and be gentle, and you will end up with a 
nice looking retaining lip.  Then carefully cut the other end of the 
form/aluminum square and to the proper length for the holder you envision.

I did this for a couple of scopes when I didn't have time to buy and 
wait for a secondary holder to arrive.  I also made my own holder for 
the 4" secondary of my 12.5" Cassegrain, since that is a custom item.

	Mike Lockwood

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