Re: [ATM] Re:Tees instead of triangles

[Kevin Whitefire <chaosopher23@yahoo.com>]

Drilling a weld is OK if the weld is a good one.

Drilling really close to a weld is also OK, as long as
the weld is good.

Kevin

--- "Alan K. Henderson" <alankh@ev1.net> wrote:
> > 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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