ATM Re: 18" edge support: Sling or 2 wires? ... so I used both.

[Ed Taychert <elt@irony.com>]

Thank you Bob, your post makes me realize that flexure in the
"bar" will not cause the screws in the triangles to hit ...
otherwise, I have to disagree with you -

The 1/4" plywood triangles are carbon fiber covered and are
"WOW" stiff ... in the mirror sizes that I'm working with,
30 to 50 pounds, they never carry more than 5 pounds and
there will be absolutely no concern that they are strong
enough. Even in the 27 point cell that I made for my 26"
mirror - http://www.irony.com/Ed/astro/26inch/26inCell.html
the bottom triangles which accumulate the weight from the
upper three have enough wood to them that 1/4" thickness
is fine ...

I think it's only in the long, thin "bar" that the strength
of the 1/4" thick plywood is questionable and, yes, if I
did it again I would would use thicker material or, because
I'm into experimenting with laminating, make some compound
shape (which amounts to the same thing.)

I can see the benefit of countersinking flathead screws to
lower the profile, thank you, I will try that. In the
26" cell, I was so worried that the holes were the weak
point that I inserted nylon bushings in them ... I'm over
that now, but this is only my third floatation cell and,
yes, I still have much to learn.

Thanks again,
  - Ed.


> FROM: Bob May
> DATE: 09/10/2002 22:47:59
> SUBJECT: RE:  ATM 18" edge support: Sling or 2 wires? ... so I used both.
> 
> Not too sure that I'd use 1/4" plywood for the triangles unless they are
> small.  You may have flexing of the plywood also giving a problem.  I'd
> consider using 3/8" and burying the screws in the wood a bit as you need
> push rather than pull so the head is more just holding the plywood in place
> more than holding the triangle up so you can trim the heads down a bit or
> even use flat headed screws.  You might also use a knife and remove one
> layer of the plywood around the head to let it into the wood.
> Bob May