Vintage DD turntables. Are we living dangerously?

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.

Aigenga,
"On the subject of platter mats I just want to re-iterate that I am using a lead mat glued to an Achromat. I thought that Fleib or someone else was about to try the same thing and wonder how that worked for them?"

I'm experimenting with this now, and I'm wondering about the details of your mats. I bought a 3mm Achromat thinking 5mm might be too thick with an additional 2mm underneath.
BTW, the 3mm version seems to have deficiencies when used alone.

As it turns out, once flattened, roofing lead is more like 1mm thick and weighs about 510g. It seems to greatly improve the Achromat, but I suspect it would be better with the 5mm version. The question is, would the 5mm mat with 1mm of lead, outperform the 3mm with 2mm of lead.

The Achromat is somewhat of a surprise looking like "fine" cardboard. It's more like 2.5mm and unless you glue it down the edges tend to lift if you only clamp the LP on the spindle. I find myself listening to the last 50mm of a side, for evaluation.

Like most of you I have a collection of mats. Mine includes a 3mm hard acrylic, and one of expanded foam - also about 3mm. So far best results seem to come from the lead in the middle with either the foam or acrylic on the bottom and the Funk on top. The foam combination is a little warmer. The acrylic seems faster/cleaner, but either combo sounds pretty good.

I'm thinking of die casting lead mats of different thickness/weight. A lead undermat seems to have great potential. Perhaps thicker sheet lead is less trouble.
Regards,