Need some help from PrintrBot Simple Metal users out there. I have just finished restoring my machine, but am running into one problem that I just can’t figure out. My auto bed compensation continues to be off even though my aluminum print plate appears dead flat when I hold a high end ruler up to it at all angles. I’m at a loss as to what could be happening and am wondering if others have had the same issue/found a solution. I tried the 9 point leveling firmware with no luck.
Have you checked your metal rods? I had the same problem and they turned out to be bent from crashing into the bed several times when doing some testing (a long time ago).
Either that, or your neighbor has a small black hole in the basement that is distorting your space-time… have you checked your clock lately??? 
Is it by test prints that you are detecting it is off? Could differing mass under the detection points be throwing off your compensation distance? Rods, bearings, bolts, …little tiny black holes floating around …Ernesto 
Can you do a manual level with a paper to see if it is mechanical?
When I took the rods out during tear down, I never actually tested them to ensure that they were straight. The previous owner did mention that he had been having the issue, however, I feel like I moved the rods all around when reassembling so that should have made the issue different I would think.
I can pull them out and test for straightness.
@Jeff_Parish yep. When probing it spits out values of reasonable deviation, and when I just remove the G29 and only home, there is a significant slew still.
I have torn my Simple apart a number of times to check rods, the build plate, you name it. But recently I was watching my printer to ensure that all important first layer when I noticed something I will be fixing this week. I use BuildTak, and most of us have used the blue tape or some sort of masking bed prep to achieve adhesion and maintain our investment. Well it seems my print bed, and many I have spoken with report the same, is low on the home side (left) and high on the right side. Our printers use an inductive sensor to measure the z height, which is located to the right of the hot end and most of us only mask off the needed print area so as to not be wasteful with our materials. With the 3 point probe the first two points have that masking material below the inductance sensor. This bed prep material to an extent insulates the metal bed underneath it much like rubber insulates electricity in an appliances power cord, which causes the sensor to get closer to the prep material as the first to points are probed. The third and last point, as you can see in the photo, doesn’t have that insulating material blocking the sensor under it so it picks up the flux field at a higher height and adjusts the three point plane to seem as if it is skewed even though the print itself will be on top of the bed prep material and slightly higher than the point that isn’t covered and triggered the sensor more easily. The whole thing skews the entire print plane even though the bed may be flat, and the skewing is exaggerated by the thickness of the bed prep material plus the additional height that the uncovered probe point triggered higher at.
I ordered a piece of PEI that is 9.25”x6.25” and will use it to cover my whole heated bed, probably trimming it down to about 8.5”x6.25” so that each probe point will have roughly the same inductance potential and register with the sensor at reasonably the same heights. I hope this sorts out the skewing of the print bed, cause I really don’t think it is that far out. As is now a print barely adheres on one side while being smooshed completely flat on the other side of the print bed, so smooshed sometimes it clogs my hot end momentarily.
Those are my thoughts on why the bed seems warped.
@Matt_Olsen that’s exactly the problem I am having, aside from it being the other corner. Mine is fairly far out but seems consistent. I’m considering moving the probe offset a little to see if that fixes it.
@Brook_Drumm any thoughts?
I do manual levelling using Simplify3D’s wizard with a piece of paper so I have never experienced this issue (even though I did install the sensor and the optical coupler but never bothered to connect them because the new bed supplied by Reliabuild is so flat it makes the entire process unnecessary). If you suspect it is the sensor, perhaps try using Marlin’s manual levelling as suggested by @Jeff_Parish and see how it goes?
@Brook_Drumm my dumb fingers managed to delete your comments, but I read through it. It seems very logical to be a torsional issue if the bed isn’t warped, which it truly isn’t.
That being said, I will take out the rods and see if any themselves are warped, then proceed to test axis’.
@Ernesto_Martinez I am keen to keep the machine working as intended from the factory. Really want to know that it is indeed automatically compensating correctly.
@Griffin_Paquette I have my older built Simple Metal (not in use now for 1,5+ year as I run showroom with different brands), but as I remember my firmware plays on it, only 3 points levelling works on this Printrbot. (I had upgraded/longer axis and Al heated bed.)
So what did Brook say? It would be nice to know what advice the creator of the Printrbot would have to add to the conversation.