Printer Will Not Print Straight Walls

Hello, I have been struggling with a strange issue on prints from my homemade 3D printer. Whenever I print vertical walls, the print looks "wavy" or shifted, and this waviness occurs in both the x and y axes . I have attached a picture of the issue to this post but I'm not sure if it will show up. The two prints are Esun PLA+, printed at 210 degrees and zero per cent infill. The one on the left has 1 shell and the one on the right has 3. The extruder is a direct-drive type.
Things I have tried to fix the issue:
-Tightening/ loosening belts
-Adjusting stepper current
-Replacing z axis couplers
-Checking for bent lead screws
-Trying different print infill densities
-Trying different numbers of shells
-Switching from Slic3r to Cura
-Trying different print temperatures
-Tightening grub screws
-Changing flow rate
-Changing microstepping
-Using different materials
-Changing acceleration
-Printing slower/ faster

Any help would be appreciated.

Edited 3 time(s). Last edit at 12/24/2019 11:16AM by Yuoiea.

Are you using bang-bang control of the bed temperature?

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

No, I do not have a heated bed.

Edited 1 time(s). Last edit at 12/24/2019 01:43PM by Yuoiea.

Post some pictures of the printer...

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Do these waves always appear at the same height in the model? If so > Z-wobble.

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http://www.marinusdebeer.nl/

It's kind of hard to tell, but the waves seem to occur at around the same intervals. However, the waves appear with varying extremes in different prints.

Here are some photos of the printer.

I am printing on a very wobbly table, would that cause this issue in the printer?

Looking at your machine, I think it is the best "quality' print it can and will ever produces.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Yes, in terms of print quality, I agree. But no machine is expected to produce prints that lean in different directions; there is clearly an issue occurring.

Those tiny pictures are just about useless. Can you get some higher resolution images?

Each axis should move very smoothly without the belt/screws connected. There should be no sticking or wobble in the motion. The extruder shouldn't wobble or tilt. Grab the hot-end (while it's cold!) and try wiggling it. It shouldn't move without significant force applied. Motor mounts should be rigid. Guide rail mounts should be rigid. Guide rails should be thick enough to minimize flex. Belts should be tight, but not too tight.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

More pictures, hopefully clearer.

All of the belts are tight and each axis moves smoothly. Everything seems rigid except for the extruder mount. I am using LM6UU bearings, it a bit of wobble normal when pressure is applied?

A few things that may or may not be related to your problems with the prints:

1) the Y axis belt is wrong. The part that connects to the bed carriage must be kept parallel to the Y axis guide rails. The same is true for the X axis- the side of the belt loop that connects to the extruder carriage has to be kept parallel to the X axis guide rails.
2) your print cooling fan duct probably doesn't blow any air. Axial fans don't work against back pressure that is created by the duct. See: [vimeo.com] and [vimeo.com] Look for a duct design (or make one) that uses a radial fan
3) it is common practice to leave the non motor end of the Z axis screws free so that bent screws won't cause the X axis to wobble. If the X axis wobbles, the extruder nozzle will wobble and create Z axis problems in the prints.
4) the guide rails look really thin, and the Z rails are thinner than the lead screws. Any misalignment or slight bend in the lead screws will cause the guide rails to flex.
5) the cables to the extruder may be putting some drag on the motion of the extruder carriage along the X axis. You're using very small motors so you can't afford to add any drag. Try hanging the cables from above. Feed filament to the extruder from above, too.
6) the bed is supported on screws and springs. Every time the bed reverses direction, it may wobble a bit depending on how firmly the bed carriage grips the screws.
7) the X axis motor appears to be tilted by the tension on the belt. That shouldn't happen.

Edited 1 time(s). Last edit at 12/25/2019 01:04PM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I removed the bearings from the top of the z axis and that seems to have reduced the issue, especially along the Y axis. However the X axis remains pretty much the exact same and even the y axis is not very good. I made sure the belts were parallel to the rails, there was no improvement. As for the cooling fan, you are correct when you say that it does not blow any air, thank you for suggesting that. However I find it unlikely that that would be causing uneven walls, because I have done several prints in ABS that have the same issue. In a few days, after I am back from a trip, I will organize the extruder/ thermistor/ fan/ hotend wires so that there is no chance of dragging. I already feed filament to the extruder from the top. I may be wrong, but I don't think the bed springs are causing the issue because the issue occurs even at very low speeds.
Thank you for all of the help so far.

My printer's idler pulleys are fastened with screws that are maybe a little too small for the pulleys' internal diameter. The pulleys can move forwards and backwards in their socket because of this setup (they don't wobble, though) Could this be causing the issue I am experiencing?

The wobbles on the 3D prints seem to occur at regular intervals. Does this indicate a particular cause of the issue?

Normally its Z lead screw wobble. Ie the Z lead screws are bent and although the bottom may be fixed and even the top, the middle bulges in and out when rotating.

Edited 1 time(s). Last edit at 12/26/2019 12:57AM by Dust.

I checked my lead screws, they are not bent.

I think my z axis is not parallel, I will check in a few days.

Edited 2 time(s). Last edit at 12/26/2019 12:47PM by Yuoiea.

Looks like the connector between the Z motors and the Z lead screws needs to aligned. Your lead screws are bigger than the motor shafts so may have selected the connector based on that size. If you have the same size hole (must be large to suit the lead screw) when you clamp the motor shaft it will be off centre. This will displace the lead screw in X and Y as it rotates. Seems to be your problem.
Quick fix would be to print/make a sleeve to go over the motor shaft to match the diameter of the connector. Or wrap the shaft with tape as a temporary solution.
Check the fit of the lead screw into the coupler aswell.

That was similar to the problem. As it turns out, the brackets holding the tops of the z axis rods were misaligned. After re-aligning them and printing new linear bearings, my prints are straight. Thank you for all of your help.

Edited 1 time(s). Last edit at 01/05/2020 08:48PM by Yuoiea.