Skeletal vs Plinth style turntables

Silence killed the comic....

and apparently this thread :^(

The good news is Sunny weather, with above 0 celsius temps are in the forecast which should mean an end to the cabin fever rants.

Happy listening.

Ct, For what it's worth, I built two plinths of the type you describe. Both from slate slabs, and I was motivated not only by the principle that there should be a rigid association between tonearm pivot and bearing/platter but also by the simplicity of the design. Simplicity is a virtue when you work with slate, because it is so tricky to cut slate without having a disaster. On the other hand, my favorite Einstein quote is to the effect that the solution to a (physics) problem should be as simple as possible, but NOT simpler. As a result of my perhaps too simple plinth design, I am limited to tonearms that bolt to the top surface of the plinth and which do not require a pass-through for a vertical shaft. Thus I have a collection of such tonearms: Reed 2A, Triplanar, Dynavector DV505 (two of the latter, in fact), RS Labs RS-A1 (the funkiest but actually sounds great). Both my Denon DP80 and my Lenco L75 reside in such plinths. For my SP10 Mk3, I did revised the basic idea so as to accommodate removeable tonearm mount boards, made of slate or aluminum. Yet the Reed 2A is king of the Mk3. And the Mk3 plinth uses constrained layer damping; the bottom half is solid cherrywood.

For the TT101, I took the base QL10 plinth and extensively re-vamped it with heavy alu supports below deck to stiffen it and with an alu arm board to replace the supplied particle board one. I further stiffened the tonearm mount by bolting the alu "board" through to a heavier piece of alu below deck such that the wood of the QL10 is squeezed by the alu arm board from above and the stiffening alu support below. We shall soon see whether the TT101 will continue to function reliably when I re-install it in nude form into this plinth.

Hi Lewm
Just to give all parties an update. I have gone with a bit of a balanced mix of compromises so to speak in my grand plans. But just so as to whet a bit of your appetites I have ordered 6 pieces of aluminium thus far - they are to be chamferred then anodized.
In addition to this I have sourced panzerholz as well. I have also ordered some pieces of Corian.
I will add that I now have access to CNC machining facilities, and have been banging out dimensions on my graph paper (can't figure out Autocad)
It must be said that sourcing parts can be a real pain in the neck - especially in small numbers.
I am still umming and ahhing about the use of some Lexan in its construction.
I can't say much more save to say that it is not all about mass or damping. I am not going skeletal either, because I cannot abide dust getting into anything.

While waiting for Halcro to answer Lew's question in his post of 02-13-15, I thought it might to be interesting to look at the pod movement thing from another angle.
To me it is obvious that it will move due to Stylus drag. The question is how much.
In order to calculate this I needed a figure for stylus drag. A search on the web proved inconclusive but then ironically the answer came from the original timeline thread. There, one TT is mentioned where specific data is given on the amount of laser pointer movement per revolution and its distance from the centre spindle.
This TT is a beautifully engineered machine with, from memory a 22 kg platter driven by a fractional horse power motor via a thread. Hereafter I will call this TT. "TD"

The specifics were 2 mm movement on a distance of 400 mm per revolution.
With this information it is possible to calculate the retardation torque and hence the drag. From this it is possible to calculate how much the pod moves.
So assumptions......
A pod identical to Halcro's is used on TD
Platter 22 kg of uniform section
Pod plus tone arm 11.5 kg
Height to record surface above mounting surface 150 mm
Pod feet 100 mm spacing in a equilateral triangle
Pod/ arm CofG, 75 mm above mounting surface
Pod CofG Central inside the mounting feet
Pod feet are not adhered to the mounting surface. ( no penetration of the cones into the shelf )
The same arm and cartridge used on TD is used on the pod.
TDs motor only provides enough torque to maintain original speed before stylus is lowered, after it is lowered.
Stylus is lowered at a radius of 140mm
Platter has a diameter of 320mm

The first answer is the force applied to the platter to cause this retardation torque. This works out at 0.0031 newtons. Actually a large number under the circumstances but it is slowing a 22 kg platter!
Using this force and applying it at a height of 150 mm to the pod we get a tilting of 8.2 microns towards the platter.

Observations.
With the stylus at a radius of 140 mm, the two front feet of the pod do not appear to be a right angles to the arm when viewed from above. This will reduce the tilt a little. It is unknown what happens to the magnitude of the stylus drag as the arm tracks towards the centre, so it is possible that the pod will tilt as calculated once the arm is at right angles to the feet assuming that this happens before the end of the inner grooves.
As an aside the tilting at a radius of 140 mm produces a yawing effect on the pod such that the arm rotates approximately along its axis. This effect is caused by the configuration of the feet. It is tiny and likely insignificant.
The calculations assume that the platter motor assembly cannot move. It can and will, but much less than the pod becaue of its wide footprint.
The calculations assume that TDs motor does not sense the slow down and produce restorative torque. Since it is a synchronous motor it will act to try and maintain speed. This will put more energy into the system and increase the tilt.
The pods appear to be slightly crescent shaped. If this is the case the CofG will be biased towards the two feet closest to the platter. This will increase the tilt.
If TDs arm and cartridge was fitted to a pod and used on Halcro's TT, things would be different again. This because the TT-101 does NOT slow down. It is putting more energy into the system, so the tilt would be larger.
The calculations assume that TDs platter has a uniform section. If its radius of gyration is larger or smaller than this suggests, the tilt will similarly be larger or smaller.
Actual dimensions and weight of the pod will materially change these numbers.

I do not know if the amount of movement is of any significance but for sure it moves. This compromises one of the three ideals I mentioned featured in the mythical perfect TT. This was my starting point in these discussions.

Parrotbee.

Really look forward to seeing pics of your TT creation.
There are so many ways to build a TT, all with virtues and compromises. The art, I guess, is maximising the virtues and minimising the compromises.