Marchal
    I have used 3/4" copper water pipe for the support frame.The joints are
mitered and soldered. The geometry isn't to complicated. One triangle in
the horizontal plane at the bottom(vertex at the hinge end) and one
triangle from the top flexture and meeting the lower triangle at the boom
free end , and one single vertical for the rear mast.  I believe in
triangles(not to much flexturing). Triangular shapes will result in mostly
axial loads and are stiffer. I like the tension hinge arrangement shown on
Sean Thomas's web site, though I have been successfully using knife edges
with my seismometer for years.
Just a little more input.
Regards
 Barry

Marchal van Lare wrote:

> Hello Meredith, Angel and others,
>
> Thank you for your recommendations.
>
> Yes, I use the original Lehman knife edge design, since its
> quite unstable, I am gonna try to use Angel's version.
>
> Tomorrow I will check a local machine tool store, to find out
> if they have some surplus materials.
>
> I am thinking of a 20-30 cm wide frame, to get it as stable as
> possible.
>
> I will let you know more tomorrow.
>
> Thank you for your help.
>
> Best regards,
>
> Marchal van Lare
>


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