Re: [ATM] New Project

[Dominic-Luc Webb <dlwebb@canit.se>]

Hello Jake, others,

The layout might be OK. The materials used are important
information, and it looks like you have a few different
materials. This could be good or bad depending on the materials
used and how they are attached. We also do not see any
measurements. I see what looks like some elegant routing on the
inside of the ends, and that makes me wonder if this is a
functional design feature or the results of a recent acquisition
of a new router and (box joint???) guides.

As regards materials, a friend recently explained/reminded me a
very elegant concept of temperature compensation by combining
materials with different thermal expansions. Configured properly,
a tube/cage, etc could effectively show little or no change with
temperature fluctuations by having their expansions opposed.
This does nothing about the optical elements themselves, and I do
not know how far this concept can go for your cage/focuser, but
this reminder made me reconsider how I choose materials and
exactly how I join them. A specific example can be seen in very old
clocks with pendulums. Anyway, I really appreciate the cleverness of
this concept, so I thought I would offer it for your consideration
thinking that maybe you have not decided on materials yet.

Most immediately, you seem to have some tight routed fittings
(again, box joints???) between the wall of the tube and the
ends. The wall and the ends (ends made of wood?) seem to be
different materials, and then the rods are yet another material
(anodizing suggests aluminum). I could imagine some combinations
working better than others. How rigidly they are fastened probably
has some effects on performace.

While on this topic, has anyone made these cages from fiberglass
molds, and how stable are theses for comparison?

Dominic


On Tue, 2 Oct 2007, Jacob Lauser wrote:

> I started my new dobsonian today after roughing up a basic CAD of the
> secondary cage. It's nice to know my CAD skills haven't totally
> deserted me. The tubes are laid out on the floor of my room polished
> and ready for anodizing!
>
> What do you think of the cage design? The I.D. is 12" and the focuser
> is a Moonlite Crayford (for scale)
>
> http://www.atmlist.net/contrib/23tauri-at-gmail-dot-com/secondary_cage_blue.jpeg
>
> - Jake L



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