In my fs52es Aigner rail install we noted that the walls were not parallel or even plumb due to the need for a casting to come out of a cast cleanly. The taper was accounted for by some
m8 steel leveling washers from McMaster recommended by brian holcombe. We could only fit one with the hardware we had and I didn¡¯t want the play on both sides of the wall so we used one on the inside. and the outside was reference. The slight sag was not an issue. Things work fine but one of my Aigner tables has some bow along the length I need to deal with or swap out with another used in a less critical function. I recommend the washers.
