I recently purchased a milling vice from one of the usual internet suppliers in the UK expecting to have to true it up when I received the vice. Needless to say I was not dissappointed, however no mater how much time I have spent tramming up ( and adjusting ) the jaws to make sure they are perpendicular to the milling table, when I clamp a piece of metal in the vice to machine the piece of metal tends to lift up , off the parallel supporting and aligning the piece of metal to be milled.
Is this a feature of milling vices or am I missing something in my approach?