I made my machine more Zeiss like by mounting the overarm pivot on an eccentric. So far, I've used this setup only while figuring. In the configuration shown here, the turntable speed is 11 rpm, the sidearm eccentric speed is 33 rpm, and the overarm eccentric speed is 5 rpm. I typically use 1/2 inch or less in the overarm eccentric offset.

Some say that an overarm eccentric just adds new parameters to track. The way I use it, I view the added motion as being so slow and so small it only acts as a blending motion to help in avoiding zones. In all honesty, my experience level is so low I can't tell you whether or not the overarm eccentric actually buys anything, but it is something to play with.

To add the overarm eccentric shaft, I installed a second bearing support beam and a bearing box. One end of the support beam is attached to the main bearing support beam and the other end is attached to a cross brace. The 8" pulley on the eccentric shaft is turned by a 5" pulley on the turntable shaft. The bearing box rides in slots that allow tensioning the belt.

Take note of the keyed turntable shaft. This wasn't a good idea as it introduced a lot of slop in the turntable. I went back to using just a set screw in the turntable support pulley.

I was experiencing problems with the eccentric platforms lifting up from the support pulleys so I added some hold down cleats (light colored trapezoids). The original dogs (dark triangles) still supply the torque.