Inconsistently Slanted Prints

Okay, so this one has a little bit of backstory. To make it short, at my school this guy built a big printer (600x600x600 mm cubed print volume), for the student design center, but then he left on co-op before it was functional. So my team lead threw the project to me as I built my prusa i3 this summer and have been printing things for the project.
I got the printer moving, and recently mounted the build plate and started doing test prints. After adjusting the steps, belts, current, and slicing dozens of different ways, the prints are maddeningly slanted. See attachments. They always slant forward in the y direction, and sometimes back and forth in the x. Z is fine, oddly enough. Tightening the belts helped circularity a bit, and the x slants, the y axis remains off. The odd thing is, the slant is not consistent. that is, it's not constant up the whole part but changes angle. It is the same across multiple prints of the same object. The change in angle seems to be linked to the amount of detail/moves in each layer, as it gets steeper as detail increases. Any suggestions to try or solutions would be welcome.

For me it sounds like your y and x is skipping steps, the the belt tight enough?

The belts are as tight as I can get them. They all thrum like guitar strings.

Belts might be too tight then. Skipping steps is not due to loose belts slipping on the drive pulley it is due to steppers not having enough torque to move the axis. If the belts are too tight it might load the steppers down and worsen the problem.

So there are a bunch of things to try. Moving from least expensive to more.

First, decrease the acceleration, jerk, and speed settings in firmware. With increasing detail comes increasingly small moves. If the printer is trying to move an axis back and forth too fast it will skip steps. Some firmware has a separate setting for max speed or frequency for small back and forth moves. You can always find a speed at which the skipped steps stop unless you have pathological friction problems.

Next check out your stepps per mm settings for filament. Print a solid object. Is it over-filled? If so then adjust. Small spaces that get over-filled can stick up into the next layer and grab the nozzle causing skipped steps. You will see this one during a print if you watch closely.

Next, disengage the axes from the belts/steppers and move them manually. Can you feel any friction? Do you feel any stickiness when starting motion from a stop? (Stiction?) If so you might need to rethink the bearings or bushings you are using. Or just lubricate them.

Decrease the mass of the moving portion of the axis if possible.

Get higher torque motors.

There are probably other issues that might cause the same symptoms. Badly printed pulleys binding on the belts, some part of the printer hitting some other part, etc.

Bryan

I had a weird issue like that once. Have you checked your plastic spindle is getting stuck? I dismantled, cleaned and reassembled my printer and it still did it. While watching another failed print I noticed the spindle jerked. It turned out there was a nodge in its centre that caused just enough drag to jump some X steps - but only when the carriage was at the right angle and I wasn't looking.

Hi
I have had good prints, then the next one started skipping steps. everything is tight, and it runs smooth for the first layer then gets off set.
I am thinking of increasing the POT, But my question, do I need to disconnect everything to safely use my meter with the USB connected, to see what my POT setting is. OR can I just check it with everything connected. . Obviously power will be off.

Thank you