Have you adjusted the gibs before making your measurements? A poorly adjusted gib could make a difference if the table was well of its centre point, particularly on the long travel.

Shims under one side of the column.

But only after checking head to table squareness – this isn't an un-keyed round column mill where workpiece registration is lost when the head is moved.

It is just as important that the column is accurately square to the table in both planes to mantain tool position when the head is raised or lowered & just shimming the column to correct a spindle alignment issue without regard to column alignment will just be shifting the problem for one area to another.

As a former colleague (a rather crusty machine tool fitter, apprentice trained at Asquiths in the early '60s) use to say at my last employment "Build 'em right from the bottom up, or you just make problems for yourself". You can't look at one check in isolation – start from the bottom & work your way up. Fix any issues as you find them – that way you will fix the particular problem without introducing other problems as you go. You can see the required order from the Schlessinger test protocols for the type of machine, as these specify the order in which checks are to be carried out – spindle alignment ( "tramming" ) is amongst the last checks to be done, so you would not just "jump in" and do that check first.

Sadly there are no reliable short-cuts to a properly aligned machine tool – if there were, be assured that by now the Yorkshire based machine tool builders would have found them !

Nigel B.