Vintage Denon Direct Drive Turntable

I sourced a nice big slab of slate for just £30 on the weekend from a reclamation yard, it's 2 inches thick and the plan is to cut in in half and double it up, so it will end up being 4 inches deep which is the same depth as the DK300. The upper & lower layers will have different cut-out to refect the shape of the motor unit, with the lower (base) layer having a larger surface area for greater flexibility fo locating footers.

This plinth is going to be monsterously heavy, I would imagine total weight with DP80 motor unit will approach 100kg. I am intending to use Clearlight RDC cones and combi-bases as footers, but I am wondering what to use between the two layers of slate (if anything at all) if the two layers dont sit absolutely flush with one-another. Does anyone have any ideas as regards the best approach, i.e. a thin layer of compliant damping compound to isolate or something solid like small spikes to tightly couple the two layers?

Treehugga, The weight of all that slate so dwarfs the weight of the DP80 chassis that the latter is irrelevant. The big thing is how to couple the DP80 to all that mass, so it can do some good. Are you going to drill all the way through both layers of slate, so that three very long bolts can couple the DP80 to both layers? Are you going to use any adhesive between the two layers of slate or only the force of gravity, which is considerable in this case? How will you mount a tonearm? (I ask these questions, because I am thinking along the same lines.)

Hi Lewm
These are all interesting challenges as you are no doubt aware. Coupling the chassis to the plinth is the trickiest challenge. I like your idea of bolting the chassis right through to the bottom where it can be firmly anchored underneath - good one! The bore holes will need to be precisely aligned and ideally drilled through both layes in one go, which could be tricky. I had considered glueing 3 cabinet inserts into boreholes in the slate that would accept a small machine bolt as I'm not convinced that a good enough thread can be cut into the slate for a bolt/screw to bite into.

I'm not convinced that the two facing layers will be completely flat and smooth, so I wont be glueing them together, also I would like to keep the plinth modular because of the sheer weight. I'm more inclined to try sorbothane between them.

The tonearm hole also presents the same challenge, do you think a threaded hole can be cut into slate that will be good enough for screws to bite into?

(1) I have done the thought experiment as regards threading the slate. I don't think it would work. I am not going to try. I think the only choice with slate is to just drill a hole thru and then use a nut and bolt. There IS some appeal to the idea of threading the slate, because it would make for better coupling in theory. But I think the slate would just crumble if you tried to tighten down the screw. You might experiment with a scrap piece of slate, though.
(2) If you have the slate slabs honed, the sides would be plane parallel to each other and there would be a close fit between the two pieces. Most mills can hone the slabs, at least here in the US. (I had it done in Vermont and in Pennsylvania, by two different companies.) I don't think you need adhesive, but I do think that sorbothane is a bad idea. It would essentially de-couple the two pieces of slate, when what you want is good coupling. Just my 2 cents.

I've had a look at a similar thread on another forum, and agree with you Lewm that bolts are best for this job! I have decided to bolt both chassis and tonearm through the top layer only, I will drill a rebate/countersunk hole into the underside in order to secure a washer and nut, that will remain flush when placed on top of the base layer.