All steel, no welding, 2000x1300x250mm

[Wal]

Yep, It's not just achieving the consistency in your method that'll give you a problem - the height of the rail will also depend on the torque of the bolts - as such it's going to make measuring for the ball-nut bracket fitment a real pain... You need to be designing around what you know - data that is readily available, not "Oh, I'll just put these rails in using the maddest method I can come up with and then see about my ballnut bracket later.."

Heh, the rails will probably resemble a roller-coaster by the time everything's torqued up anyway. Using this method the ballnut might just move smoothly along a couple of inches of track...

Honestly, don't pursue this inviable method..! It'll be a waste of your time and money. Enough said.

Wal.