The problem is likely that the miter slot is .750" Most miter bars are .750". A .750" bar won't slide freely in a .750" slot. Commonly miter slots are slightly over .750". Craftsman (and some Ridgid saws I believe) use undersized miter bars. At one time woodworking shows had vendors with undersized UHMW strips to use as miter bars. I don't know if they can still be found or not.