When the user installed the 2 steel collars, one on either side of the wooden disc, they placed the collars to tightly against the wooden disc so it is now pinched between the 2 collars and the disc cannot turn freely.
Solution, loosen the set screw in one of the two collars and raise it up (or down) slighly and then retighten the set screw.
The disc should not wobble but it should turn freely.