[ATM] Octagonal Cage-Style Tube Design?

["Polaraligned" <polaraligned@verizon.net>]

> From: "David Sleeter" <d.sleeter@roadrunner.com>
> Subject: [ATM] Octagnal Cage-Style Tube Design?
> To: <atm@atmlist.net>
> Message-ID: <GAEAIKBHKIGEOBPBDNHNMECBDBAA.d.sleeter@roadrunner.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hi Folks:
>
> As I mentioned in a previous post, this coming year I hope to start 
> building
> a permanent computerized alt-azimuth mounted observatory scope around a 
> set
> of full thickness F/6 Newtonian optics. In considering a good tube design,
> I'm leaning toward the octagonal style, to be fabricated from aluminum or
> steel tubes and machined or welded aluminum or steel rings with
> cross-bracing beteen the rings (ala the old 100" Hooker telescope at Mt.
> Wilson).

Not a good tube design.
Serrurier truss (or derivitive) is a good design.

See image of 32" tube that I am currently constructing for ideas:
http://img.photobucket.com/albums/v223/polaraligned/ModIO/32INCHASTROGRAPH-Model1.jpg

It is all steel construction because pound for pound, aluminum is only 5% 
stronger
than steel but has a thermal coefficient 3x that of steel.  Steel is a 
better choice.

Why would you want to build an alt-az mount for a permanent observatory?
If you are going through the trouble to make a nice machined metal mount
an eq wins hand down.  EVERY commercial research quality mount out there
in the small to mid size scope class ( up to at least 40"), is built on an 
eq mount.
Some type of friction drive is best, but worm gear drives can work with the 
right
drive/software.
I prefer a friction drive split ring/horseshoe but fork is an excellent 
choice in your
size range.

Scott






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