Another Newbie

[EddyCurrent]

I designed the machine on Sketchup which enabled me to determine the lengths for the ball screws and rails but I did not start to build until they arrived because then, as you say, I built the machine around them. Having sad that the items arrived exactly as I ordered. You could therefore buy a generic set from ebay and design the machine around those.
Yes I paid VAT and import duty on the amount I was invoiced for, the bill came from the courier in this country.

[JAZZCNC]

No you don't pay import duty from China on ballscrews or rails.? You pay VAT and shipping admin fee which is any where from £10-20 depending on who shipped it.

Both ways works but designing in CAD is much better IMO as it will highlight any clash of components or nasty surprises down the road. It also gives you something to referance from, Just don't go silly on design taking it to emph degree.
Just the major parts need designing, so main Frame, Gantry, Screw placement/mouning etc and esp the Z axis.!. . . Then get on with building.!

Start a Build thread and post your intensions/design and Ask any questions that your unsure about and even some your sure about.? Because what you think may be the best for your needs can easily not be so better mentioning it.!

[EddyCurrent]

No you don't pay import duty from China on ballscrews or rails.? You pay VAT and shipping admin fee which is any where from £10-20 depending on who shipped it.

Yes, my mistake, I just churned out the words of the OP, I've just got the paperwork out and it's VAT and Advancement Fee (Clearance Administration Charge)