[solodex2151]

This is Nate from Fine Line Automation. The advantage of the dual screws is you can go with a completely overhead gantry, though at the length you want I would consider moving to a Rack and pinion setup. I really like an overhead gantry design for dual drive. It moves all the linear motion and powertrain components up out of the way of debris and resists racking better that a wrap-around gantry. Note that by the time you are ready to build your machine I should have 4' rails available.

Edit: I need to clarify this. I thought you were looking for a 4' travel on the X-Axis. I didn't realize it was only 32" or so you were after. In that case, a leadscrew setup is preferred and more cost effective.

Regards,

Nate