Rigidity problems on the 1500x1500 workbee solved

This isn't a question, but I figured this might be useful to others, and maybe some useful feedback for ooznest. I've always had big problems with rigidity on the 1500x1500 workbee - I upgraded it with a linear rail kit and beefier side plates, which made a bit of a difference, but I would still get terrible chatter because of the X axis twisting.

I finally decided to just do something about it and added a 800x800x3 mm aluminium box section to the back of my X axis, and my problems have now completely disappeared. I was previously limited to using 3.5mm endmills because anything larger would result in extreme amounts of chatter and vibration, now I can easily take 5mm passes in birch plywood with a 6mm compression bit.

This probably isn't terribly useful for people with a stock workbee, as it's not possible to add an extra extrusion to the back of the X axis with the stock V wheels, but maybe it still helps someone else!