Whilst I cant prove it without delving into some specs of the screws however Acme is not exactly accurate. We used them for 3d printers, they are OK to move things from rotary to linear but its nowhere nearly as good as a proper ballscrew.

Sure, there are better nuts available (delrin etc) but it simply cant be as good, surely? I would have guessed (and its a guess) that the tolerance difference must be large between acme and ballscrew.