The big machine works great for big stuff in a single pass, especially since you won’t be as likely to notice the inevitable sloppy tolerances a build that size would cause. When I got to doing fine detail laser work, the flexing of my 7’ long X gantry was showing up as ‘pulsing’ in the Y direction. (Flexing, then moving and catching up, flexing again, then moving.) The pulses are small, but still a problem for lasering, and a deal killer for milling. Shown in a close up of laser cut paper.
My solution was to throw a whole new ‘Y axis assembly’ in the middle of the machine to temporarily shorten it and give me the rigidity I need. The Y stepper driver now runs 3 steppers for that axis (Didn’t even increase the current, may have been running it high before!) and I have rigidity comparable to a much smaller machine. Note that in the pics, I don’t even have the feet for the extra piece screwed down - I carefully matched them to the heights of all other supports, and they sit firm, attached to the long X pieces firmly.
With this arrangement, I can loosen the corner pieces and slide this assembly to make the working area of the machine whatever I desire. For milling, I could bring X travel down to eight inches, for super long work, it can go to the far end or be removed completely.
I’m using a physical stop with an electronic end stop to help square the long axis, (Very hard to keep the long machine square once the motors shut off!) and will be changing to two end-stops in series, carefully positioned, so that a couple of homing moves should give me a nearly perfectly square machine with less work.
I welcome your suggestions for improvement and ridicule, this probably looks quite mad to some of the originators here!