Yeah I figured the single x axis ballscrew was causing weakness - I'll get a mail over to Chai for a new ballscrew with appropriate machine end and go the pulley/belt route (seems less prone to error than two steppers). I'm looking at Zapp/Gary for the belt and pulleys if I can decipher what length belt to order (whether the length is for the whole belt or the loop if folded in half - if that makes sense).

As always thanks for the sage advice and assesment of the machine once its been upgraded (I like the sound of "beast" :-) ).

Chris