Lenco plinth? How big is too big?

Ralph, I am not sure I can properly visualize your method of mounting the tonearm, that involves cutting off a corner of your plinth. It sounds as though you intend to de-couple the tonearm mount from the major part of the plinth. There are differing opinions on this, but lots of smart guys think that the tonearm mount should be tightly coupled to the plinth and hence to the main bearing of the table. This sounds like a good idea to me. If my perception of your design is correct, you might want to re-think the mounting of the tonearm. Maybe Win and Jean can chime in on this topic.

Lewm, I had the same impression from Ralph's arm mount description and the same sense of caution.

In ongoing design for my SP-10 plinth, I'm intending to bolt down the armboards (2) with brass machine screws. Each armboard will be 3/4" thick and replace that section of the top 3/4" layer of birch ply. The idea of cutting off the end of the plinth then reattaching the arm somehow sounds questionable to me.

Ralph, concerning how big, you might want to read some of Jonnantais' experiments with various plinth materials and size.

Lew,

I am probably in the minority here when it comes to the issues surrounding tonearm coupling. I do believe that mounting the tonearm to the plinth in a secure way is indeed the only way to go, but I stop short of your comment regarding an interaction with the bearing. Still, it should be a non-compliant mount, in my opinion. All this begs many questions about isolation, neutrality and what it all means. It also goes to the issue of dissimilar materials in the build. Should that apply only to the plinth? I don't believe so. What I do believe is that every small part, and how that part is applied, counts. I also believe there are various ways to get there, and in the end very different turntables can reach the goal. It is a very complex process, and there are no fast answers...unfortunately.

Win, I probably overstated the case for tonearm coupling. As you know, there ARE those who do advocate firm coupling to the bearing. However, your opinion carries a lot of weight with me (at least 200 lbs of slate). Anyway, I think we both agree that mounting the tonearm completely outboard of the plinth is not optimal. Like Pryso, I am also building an SP-10 plinth, so these considerations are very much on my mind, too. Ralph, I hope you get the picture.

So if I understand the utility of a good TT plinth is to damp vibrations as much as possible. Layers of different materials and added weight/size matters to achieve good damping. Nature of materials too.