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Base Concept #2:
Like the previous concept #1, this base uses an assembly of alternate aluminum and pvc plates adhered with polyurethane adhesive. This method of construction will assure parallel faces from the top to the bottom of the stack-up by virtue of the precise manufactured form of the materials.
above: the assembled turntable less tonearm. Sorry, but tonearms take time to model in 3D, so please indulge me and try to imagine the tonearm as it would be mounted.
Digression:
Once, I did manage to model a complete TP16 tonearm. And while the results were somewhat satisfying, the work absorbed much time. When I start taking a closer look at tonearm design, then I'll begin modeling various different arms for the sake of study. Below is an example of a Thorens tt with the much maligned tp16 tonearm modeled in 3d.
(click on thumbnail to view full size image)
End of digression:
above: top view of the assembled base with armboard. The base will be built out of three separate structures; a main beam, a cross beam and the armboard.
The main beam, which supports one footer, the platter bearing and the armboard, lies over top of the shorter cross beam and is attached by 5 bolts screwing into the tapped holes in the main beam, as well as more polyurethane adhesive between the mating surfaces. The armboard mount is secured by four machine screws with nuts. I'll find extra fancy fastener hardware. No plain cap screws. McMasters..!
above: Perspective view of the base with the Teres bearing and BDR cones fitted but less armboard. Armboard is allowed adjustment for mounting distance (pivot to spindle) by way of the 4 length-wise slots allowing a minimum pivot to spindle of 215mm and a max of 229mm.
above: Perspective view with armboard.
One of the features that I see in this form of construction may not be obvious at first view. Even though the pvc layers do not by themselves offer much in terms of tensile strength and stiffness, the layer of adhesive that bonds the pvc between the aluminum plates will exert a horizontal tension which must be overcome by any substantial vertical loading which might wish to deform the structure. In a sense, the assembly above is a kind of leaf spring. One that will not exhibit any apparent compliance to the loads which it will carry. My --intuitive-- sense indicates the structure will be effective at damping structural borne resonance. The proof will be in the reality of the first actual base.
above: bottom view showing the recessed area around the lower end of the platter bearing, the speed sensor access hole , the 5 tapped holes for bolting the cross beam rigidly to the main beam, the BDR cone feet and the recessed access being offered for the Rega tonearm mount. Sorry, again, but I failed to model the hex nut that secures the platter bearing. Please imagine that it is there, pulling and holding the bearing firmly against the main beam.
above: looking at the armboard and its recess from underneath. Rega uses a large hex nut to secure their arms to the mounting plate. In this situation, I will need to make one of two possible things: 1) a long hex nut to allow easy access, or 2) a special purpose wrench that allows easy reach up within the confines of the recess to drive the big hex nut. I can easily imagine a modified socket wrench, slotted to pass through tonearm wires, and extended to allow hand tightening and loosening. Otherwise VTA adjustments will be nightmarish.
above: an assembly view minus the outboard motor pod, drive belt or tonearm. This view shows the lead-shot loaded Teres acrylic platter which will be used.
Some more thoughts:
Comparing this base design to the first one shows a similar method of construction ala the constrained layer build-up. But there is a significant reduction in the mass compared to the first. It occurred to me that any structure in the base that does not play a significant part in the actual load bearing of it, is merely dead weight and likely subtracts from the overall rigidity of the piece by increasing the load burden to those areas that do support the total mass. I have also repositioned the footing into a much tighter pattern around the platter bearing in an effort to increase overall rigidity.