[ATM] Re:Tees instead of triangles

["Alan K. Henderson" <alankh@ev1.net>]

> What is the advantage(s) of Ts instead of triangle plates?

A 9-point cell for a full-thickness 16" mirror (technically it's a 16.5"
mirror, counting the beveled edge) requires some rather thick metal for the
triangles. The triangles are roughly 8" along the longest side. Scaling
upward from the tables in Kriege & Berry's book, I guesstimated quater-inch
steel or half-inch aluminum. I'm not quite sure that's enough. Aside from
the challenge of cutting through thick metal plate, making square cuts in
tubing seems easier than carving weird triangular shapes out of plate metal
of any thickness.

A tee-shaped "triangle" could be balanced with a judicious combination of
drilled holes in the long horizontal section and added weight to the shorter
vertical section. I still need to know if there's any problem with drilling
so close to a weld.

The skewed-H 12-point cell looks interesting. It also looks like a
nightmarish task of keeping all the bars properly aligned. Makes an 18-point
cell look simple by comparison - just needs a single inner ring of
Kydex/fishing line/whatever.

I'm having trouble figuring out how to get Plop to design a 12-point cell.

Alan K. Henderson

---- Original Message ----- 
From: "Olivier Biot" <olivier.biot at versateladsl.be>
To: <atm at atmlist.net>
Sent: Sunday, May 15, 2005 2:43 PM
Subject: Re: [ATM] Re:Tees instead of triangles


> Alan,
>
> I'd take care of balancing those Tees, in such a manner that their COG
> coincides with the hole you intend to drill.
>
> You're planning a 9-points cell. The issue is that those triangles are
very
> "flat", hence the position of thecentre of gravity (COG) may be rather
> critical.
>
> Another probably easier cell is the lever-based 12-points cell, which may
be
> easier to build (almost identical length levers in some configurations,
like
> the 3 skewed H geometry).
>
> Best regards,
>
> Olivier
>
> ----- Original Message ----- 
> From: Alan K. Henderson
>
> Ah, I should have said those three magic words: nine-point cell. For a 16"
> full-thickness mirror. Here is a side-by-side sketch of a traditional
> 9-point cell (taken straight from Plop output) and the cell with
tee-shaped
> supports (mirror support pads and support bolts drawn to scale).
>
> http://users3.ev1.net/~alankh/Triangles-Tees.gif
>
> The mirror is thick enough that it doesn't need an 18-point cell. But the
> triangles/tees will have to support 50 pounds, so the well-established
> engineering tradition will require some tweakage.
>
> Alan K. Henderson


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