Hello!
I didn’t know that the gantry should be going down by gravity when power is off!
I have done a fair bit of troubleshooting and I explain and show the problem in this video! Thought it was easier that way 
Down by gravity is not a requirement but on mine only happens with a router in it.
Okay, Instead of just replying incorrectly like my previous reply. I finished the video.
Take your top assembly off. Your X Z rails can be checked with a square, you have an obvious problem on one side at least (when it goes up or down it should not move the side plate), this is adjusted by the XZ end caps(tighten the tops loosen the bottoms to bring the Z rails out). The other thing to check is your Z rails, measure the distance apart on the top and bottom the number should be the same.
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Nice looking build.
The plates might be twisting because only one end is moving. So it is traveling on a circle instead of just moving down. It would be interesting to look carefully at it while commanding both ends down.
The resistance is hard to tell from a video, but it didn’t look like very much. Does it get harder when you get down to the bottom?
Hopefully it is just that you don’t have the router yet.
It may also be sensitive to being out of square.
Shoot your right, move it under power with the steppers driving and see if there are any issues. I am not seeing anything major, so maybe just use it a bit and see if anything is actually wrong.
Dang Jeff always seeing the bigger picture. Thanks!
I wonder if the pipe size/weight is making a difference too.
You guys are incredible!
The pipe has diameter 25mm and 1mm thick.
I did a bit more testing.
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With router mounted and positioned in the middle: gantry is not moving down on power off.
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With router mounted and positioned at the “back side”: That side is moving down perfectly on power off. Not opposite side tho.
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With router mounted and positioned at the “front side”: gantry is not moving down at power off.
So should I disassemble top part and check for square? 
I don’t think so. For now just use it. See how it goes. Unless it is stuck or hard to move you should be okay. Lots of testing and learning, plenty of time to adjust later if necessary.
Thanks a bunch Ryan! Love your design. So easy to put together! I bought the hardware kit from you.
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I had the same problem Are both bride supports (holds tubes for x and z axis printed solid, or near solid infill? I have a smaller CNC and remilled my plates out of clear 1/2" plexiglass - super solid now the gantry drops on both axes upon shutoff
I had this after rebuilding my Y axis plates. Backing off the bolts holding the Z axis lead screw nut resolved this- I guess the z axis stepper motor mount was not square to the plate.
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