Vintage DD turntables. Are we living dangerously?

05-14-15: Richardkrebs
Dover.
The essence of an I beam and ply is the separation of the two outer layers (sheets). Any bending causes compression of one sheet and tension in the other. This increases the stiffness of the structure.

Richardkrebs, that is not correct. if you used sheets of plywood stacked vertically to make an I beam your house would sag and probably fall down. The essence of an I beam as I explained in my post is that the vertical component has high vertical and longitudinal strength, but can be flexible in the lateral direction. It has nothing to do with the layers of timber in the wooden I Beam. In actual fact plywood as you understand it is not used in the manufacture of I beams. I Beams use a special construct of layers of timber running in the same direction to give the structural longitudinal strength. Plywood has the layers arranged with the grain crossing at 90 degrees with each layer.
It might help if you look at a metal I beam to understand the concept - there are no laminations in a metal I beam, but if you removed the top and bottom of the I then the beam will flex like a sheet of metal.

Dover.

Please read my post again.

I did not say that one should make an I beam with stacked ply.
Ply AND "I" beams use a similar technique to separate the outer layers where any bending causes compression in one layer and tension in the other.

Why are we debating this???

5-14-15: Richardkrebs
Ply AND "I" beams use a similar technique to separate the outer layers where any bending causes compression in one layer and tension in the other
Why are we debating this???

Richardkrebs you described your plinth as a "form of I Beam".

05-13-15: Richardkrebs
My TT uses 2 x 30mm thick Acrylic sheets, separated and fused to a lead spacer. By separating the two structural plates a form of 'I' beam is produced since shear between the two plates is strongly resisted.
This is a similar idea to that used in the light weight wooden 'I' beam floor joists.

An I Beam consists of a Web with a flange top and bottom.
Your plinth that you describe has only a Web and no flanges.
An I Beam without flanges is structurally weak, has no axial strength and will flex. Here is a link to help you understand how I Beams work..
http://en.wikipedia.org/wiki/I-beam
There is no debate. The plinth that you built is laminated sheets of acrylic and lead and is not an I Beam, nor is it even a form of I Beam as you have claimed.

Henry, sorry to digress further from your vintage DD thread; but I was having my coffee this morning, came across this thread, and I am a bit surprised at both Dover and Richard.

All this "Debating" of I beams and not one mention of the best example of an I Beam, used for audio "on Audiogon", that I can think of anyway.

This I-Beam

Eminent Technology (ET) 2.5. tonearm. I am also using a ET 2.0 on a vintage DD.

Ct0517
Thank you, the ET2 I Beam is an excellent example of an I beam - no plywood, no lead or glue, just a piece of plastic with flanges top and bottom to give axial and structural rigidity - the whole piece being an extrusion to form the I. Richardkrebs may have forgotten what the ET2 I Beam looks like as he has removed the decoupled I Beam from his ET2 and replaced it with a much heaver M10 bolt, thus removing one of the key patented benefits of the ET2 design, the decoupled counterweight which was designed to keep the high horizontal mass of the ET2 as low as possible and minimise bass peak resonances. The ET2 is an excellent example of using I Beams and large thin walled tubes to deliver a light but rigid structure.