@tim Ahh OK. Do it's not truly infinite Y axis - just very long. So here is another thought. Have the 3D CNC router mounted on a pair of rails that run parallel to the beam. Clamp the beam to something. Start with the router at one end of the beam, locked to the rails or lock the lead screw that moves it. Machine that part. Unlock the router, move along the rails, lock the router in the new position and repeat. Essentially moving the tool rather than the work piece, which might be easier. I'd agree with @Danal that a separate controller might be the best way to handle what is effectively another axis although it might be possible using macros (think tool changer).
