Y axis skew, difficulty correcting.  

Y axis skew, difficulty correcting.

I got my mini a while back and everything was working great initially. After I became comfortable with it I tried printing something really tiny. At one point while experimenting with setting to reduce some stringing something went wrong, I heard a noise from, the other room and the printer had jumped, or been pushed, along the Y axis. While the effect was kinda neat I think thats what caused the skew.

Now I haven't been printing a lot of dimension specific things recently but I noticed things were off when I tried to print a case for a PCB, thats when it because clearer that there was some serious skew on my Y axis. just in a sub 100mm space in the middle it was around 1mm off. 

A cursory search revealed no software fix for this so I decided to print some shims to place at the back of the right (tower side) extrusion. Doing some math based on a skew check square I figured it was about 1.244mm off at the back right corner of the printing area. I whipped up a few shims and tried them out, the results were better but still not perfect.

That was all Friday I spend the weekend printing skew squares and shims. This has been less than smooth as I have to loosen the control box to get the shim back, and I feel inconsistencies in the prints and in how I tighten the hex screw that attaches the tower to the Y axis is going to make it effectively impossible to get it fully dialed in. 

For instance I have been printing these squares: https://www.thingiverse.com/thing:2563185 . The difference between A and C (thats the bottom left corner and the top right corner as it prints on the bed) minus the difference between B and D (the other corners) for a un-shimmed print is (I think, the one I am measure is unlabeled and might have thin shim in it already) is 140.62 - 141.8 = 1.18mm and the best I've come up with so far, 1.344 (or as close as can be printed to at .05mm layer height) is 141.4 - 140.6 = 0.8mm. All numbers measured with Vernier calipers.

My goal is to be able to measure the A/C size, lock my calipers to that size, pick up the square by the calipers (it holds in well) then without resizing the calibers pick it back up from the B/D corners. Does that seem like a reasonable expectation in terms of calibration?

I'm wondering if anybody else has had similar issues trying to sort out bed skew. Any tips to make this process simpler and the changing of the shims more consistent.