SO3: Z axis loose against rail

Again, I am totally new to CNC. I assembled my SO3 XL based on message board user pics and intuition. I noticed today that may Z axis carriage had too much movement in it during a job. I immediately paused the job and noticed two things: 1.) the spindle mount was quite loose (easily fixed - already tightened); and 2.) my entire z axis carriage has movement. The top carriage wheels are appropriately tight. However, the bottom wheels, while on the rail correctly, allow too much “play” (which I think probably contributed to the spindle mount loosening).

I’ve read the newly released manual and it mentions briefly how to adjust the eccentric nuts to tighten the wheels to the rail. I have had NO LUCK doing this. It seems that I just simply cannot tighten it enough to eliminate any movement.

Am I missing something? Is there a trick to this? Any help appreciated. It seems as though every time I get ready to try another run at something I encounter another issue. I knew there would be learning pains, but I’m starting to get discouraged.

Thanks in advance.

Daniel, it’s not as simple as just tightening the wheel. If you examine the nut, it should be eccentric(?), you need to hold the bolt in place and rotate the nut. Somewhere during that rotation, any slack should be taken up by the off-center thread in the nut. Once tight, then make sure the bolt is tightened without any additional turning of the nut. Hope this helps…

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There’s a little about the eccentric wheels on the wiki:

Thanks to all! I fixed this - it was indeed the eccentric nuts. I really appreciate such prompt assistance. Hopefully one day soon I will know enough to also provide troubleshooting to others.