Well yeah - where would you even start with that..?! The (possibly intermittent) backlash is something that I can live with for the moment as 90% of my cutting involves pretty low forces. I really do suspect that the ballscrews/nuts are just a bit shite and it's a problem best sorted by spending a bit more on decent running gear... BUT as suggested I'm going to be nipping stuff up again during my next clean/service. The skew (again, miniscule on the sizes I work at) is something I'd like to have a go at dialling out.