Gantry advice please

[Voicecoil]

Hey, you've got some tidy welding there! If you look here:

http://www.mycncuk.com/threads/1524-...per+motor+size

there's a very useful spreadsheet that enables you to play with and optimise weight/ballscrews/motor size. I'm not quite sure what you mean by cutting a letterbox in your gantry box, but do remember that the torsional rigidity of a box section will be significantly reduced if you start cutting longitudinal slots in it, it will become more a like a C-section/channel.