Need Help Solving Gantry Racking

[Coyote]

riddle me this Batman...after installing the gantry on my new 2.4 build I adjusted the z distance from the top of the frame to the top of the Y rails to the same distance front to back both rails. Then I check that the X distance between the Y rails front to back is the same. The X rail had a little racking so I loosened the three screws on both sides of the X rail then move it around until both sides of the X rail touch the front and back of the gantry with no play on either side. I then slide the X rail the the front of the frame, tighten the screws then slide to back of gantry. The right side of the x rail touches flush to the back of the gantry but the left side is like half a mm from touching. I tried several more times with same results. As long as I don't re-tighten the x rail screws the x rail touches front and back of gantry with no play. But after re-tightening, the left side has just the slightest play, light half a mil, when at the back. The X distance between the Y rails front and back is dead nuts the same. The Z distance from top of frame to top of gantry is the same all around. I'm I chasing my tail here because my next thought is to remove the gantry, dissemble it and reassemble again carefully checking after each step, which I thought I did. What's the definition of insanity again...I could use a good suggestion...thanks

 

[NoGuru]

So one thing that should be pointed out is the idler tensioners. If the belt tension is not right it will pull on the gantry. Make sure as you tighten the belts, you do them very much the same and retain the same distance on each side of the gantry.
So for me, I have a 130mm ruler. I have PINs in my gantry and I know from one pin to the edge of my RAMALA idlers I can be at 130mm on each side, I know I am square. Make sense?
Then I go to the back, and front fully. Then if I need to tension the belt anymore I will do 1/4 to half turn on each side to retain the same distance on the gantry.

 

[Coyote]

Found it. The left plane was not square by about 1mm. Or at least the issue went away after I squared it. Of course it could have been the old adage that "once you have suffered enough, things work"...either way I'll take it..