QU-BD Revolution XL Review Part 2

I have spent hours upon hours putting this machine through its paces under grueling conditions and have much to report, both good as well as things that can be improved upon.  I will start with the good, actually, great.  This thing is as fast as it gets.  Check out the 3D printing of this Samsung Galaxy 4 case (http://www.thingiverse.com/thing:100129):

My adventures have not been without their frustrations and it is only fair that I disseminate them.  I have bathed in frustration for a few days now but I really have nobody to blame.  I have concluded that some of my problems were likely caused by software.  I originally installed Repetier Host on a family computer.  When evidence of Y-axis slippage showed itself, I jumped on hardware, probably mistakenly, but because I had experienced axis slippage in my reprap past.  After loading the software on a new laptop, things went better -- until they didn't.  I had to abort that flashlight-lit Galaxy phone case print when I noticed that the LM8UU linear bearing that supported the right side of my Y axis had shimmied loose:

I can see that a red adhesive had been used to adhere the bearing to its Y-axis parent, but not successfully.  I will ask Nathan, the head engineer at QU-BD what adhesive I should use to make sure it stays put the next time.

The second problem that I encountered is more important, notably the Z-axis end-stop.  The X and Y end-stops are not that important because they do not dictate one of the most critical factors in 3D printing:  how close is the first layer to the bed.  I have found that the mechanical end-stop on the Z axis of the RXL to be finicky.  On a couple of occasions, I tried to home my axes and the Z end-stop did not trigger.  This was bad.  I quickly hit the Emergency Stop and then spent some time re-aligning the bed.  Right now, there is no good way to calibrate the Z axis.  There is a screw-hole at every corner of the bed but only two screws were installed.  This leaves the mechanical Z-limit switch -- something that I have found works differently from one moment to the next.  Home it when the bed is cold, it is a certain distance from the bed.  Try it when the bed is hot, something different.  Right now, the only way to tweak your Z limit is to carefully bend the Z limit switch lever.  My suggestion to QU-BD is that they leave mechanical end-stops on the X and Y axes but that they substitute their Z mechanical endstop with something more precise like a hall-effect end-stop or opto-end stop and that they provide a screw to adjust it.

I don't want to seem overly-critical.  This is nothing short of a groundbreaking machine.  When I look at it, I see a labor of love;  something I would be proud to release to the world.