Raschemmel ide seem to be the most possible even though I did not understand completely. Do you mean to make kind of canal in the side of the turning plate so the encoder wheel will fit on it ?
No, that's not what I meant.
To get an idea of what I meant. Get a wire coat hanger and dis-assemble it.
Straigten it out .
Now lift the turntable up about 1/8" and slide 3" of the wire under it and then let the turntable down on top of the wire so it
holds it there.
Now measure about 4 inches out (horizontally) from the turntable and make a 90 degree bend in the coat hanger to it points at the ceiling.
Now squat down and site across the turntable and make another 90 degree bend in the coat hanger TOWARD the turntable at the level about 1" below the surface of the turntable so you have a total of two 90 degree bends so far (one up, and the to the left toward the turntable)
Now cut the coat hanger about 2 to 3 inches from the edge of the turntable. If all the dimensions are correct, if
you look at the coat hanger from the side and imagine that it represents the cross section of a 1" wide piece of aluminum or sheet steel , the same length as the coat hanger and with all the same bends in it. , then if you drilled a hole in the center of that 1" wide piece of metal at the place where it is closest to the turntable (but about 1" below the surface) and mount the encoder
shaft pointing up, when you tighten the nut onto the threaded part of the encoder, you can mount a rubber wheel of the type used on RC model airplanes or cars onto the shaft of the encoder and the wheel will make contact with the turntable causing
the encoder to turn smoothly. The proper way to do this is have a machinist make an adjustable base with a threaded lead-screw
so you can adjust the distance of the encoder/wheel assembly from the edge of the turntable the wheel is rolling on.