prints turning out Diagonally skewed.

Hi Reprappers! I cant seem to print a circle. I’ve checked my XYZ calibration numerous times, but I don’t think that’s the issue. Since I’m trying to print a circle I’ll explain the situation using a clock. The circle starts off bad by just having a straight line along the x-axis at 6’oclock, then seems to do fine when it moves positively along the y-axis. As the printer reaches 12’oclock, it the print has gone too far in the negative X direction. Again a straight line at 12’oclock on the x axis. Lastly while moving in the negative Y direction, the length seems compressed.
This seems to result in a kind of ellipse with 2 sharp corners. If it would be stretched or compressed in only one direction, I know it would mean that my calibration is off, but stretched Diagonally? Any advice?

Often these things are mechanical. I'd check each axis for free travel and slop. Make sure all the nuts and bolts are tight. That includes things like the ones on the gears on the motors. If you haven't done one in a while, a clean and lube might be in order.

If it's electrical, it's just about got to be a motor driver heating up and cutting out. What you show is not at all the normal signature of that problem.

Y pulley slip or belt tension

Already tried the tension... about a cm of free tension on the x axis belt, and 3/4 of a cm of free play on the y belt. Too much free tension would make ovals.

Where would you lube? the inside of the motor (o_0)?

turned out to be the little bolt on the y-axis motor. Thanks for the help!

Basic clean and lube on an i2 or i3:

1) The Z axis drive screws need to be wiped down with an oily rag every so often. They tend to be curd magnets.
2) The smooth rods seem to stay fairly clean. Wipe them down once a month or so.
3) After each wipe down put a drop or three of light weight machine oil on each rod
4) Run the axis back and forth (or up and down) to get the oil distributed

Types of oil are a religion with people. This is my way to do it. It's not the only way / perfect way / better than every other way. Use whatever oil you've got / trust. You want a low viscosity oil rather than something super thick. Think of 3 in 1 oil rather than transmission fluid. A little lithium grease would not hurt anything on the gear on your extruder. If you grease it, it'll attract crud. It's an optional thing - less wear / more cleaning.

While you are doing the clean and lube, make sure everything moves easily and that there is no end play on x or y. Make sure that the little nuts on the z axis are still seated and are not packed with crud above or below them. It's probably a good time to do a quick check on your bed to be sure it's still level as well.

Great info. Thanks a lot.