... 1980s. That's why I started this separate topic to cover the track design aspects. Here is something that will be possible. If you omit a timber when shoving, its chairs go too, as you can see. However, if instead you set its length to zero, making it invisible, its chairs remain unsupported on the rails. Adjacent long timbers can then be extended under them: 2_301256_010000000.png With the timbers invisible, shoving them along will be a way to slide the chairs along the rails to any desired position. 2_301320_510000000.png UPDATE: We now have the keys, and outer jaws on the S1 chairs. Gold-plated: 2_061704_070000000.png Notice the random key positions (and screw heads). There should be a corner radius around the top of the jaw, but I think I'm going to draw a line at this. I've used as much of the REA drawing as seems reasonable. I'm hoping that the 3D printer will smooth out some of the sharp angles: 2_061707_200000000.png Now for the inner jaws, L1 chairs, slide chairs, slab& ...