The original solution involved a very thick disc which could then leveled and re-pitted. The problem was that the change in mass over time made it hard to calibrate the acceleration.

It also put a high radial load on the spindle whilst mounted sideways which led to run-out.

And flooding the area with radon (a heavy gas) helped the disc to float a bit, but had unexpected consequences...

It comes years too late, but I finally understand the reliability problems I had with a DVD drive mounted on its side. If only I'd had your insight then, I could have taken the PC to a playground and burnt disks on the carousel.