[SOLVED] y-axis wobble and XYjerk

Here are a few 2cm cubes with different XYjerk settings:



From left to right the XYjerk settings are 50, 100, 250, 500. I printed the 500 one twice after I printed out all of these and got the same result as the 500 cube in the image -- showing that the effect is indeed bound to XYjerk in some way.

Notice how on the lower ones, the side is never smooth -- it's slightly wavy. But with the higher values, the side slowly juts out but then snaps back to perfectly smooth at the right place.

If I use values lower than 50 (tried down to 10) I don't get any bit jutting out but the entire surface is wavy instead.

The cube printed with an XYjerk of 250 also jumped a tiny amount on the x-axis as well.

Some info:
* box frame prusa i3
* RAMPS w/ marlin
* acceleration 1500 (tried both lower and higher)
* sliced with cura
* print speed 35 (infill 45, travel 130)

EDIT: fixed image

Edited 2 time(s). Last edit at 10/17/2014 12:00AM by wentam.

More information:
* if I print with a speed of 15mm/s for everything the issue still occurs with no changes (so I'm not skipping steps)
* I can't find any backlash in the y drivetrain -- if I push on the y-axis with the motors on, it stays still until the whole printer moves.
* I've printed a few more cubes below 50 XYjerk (down to 5 this time) -- they actually still have a portion that "juts" out. If I line them all up from smallest to largest XYjerk, a sine wave is formed by the points that jut out. perhaps resonance related?
* I've checked the pulley grub screw and it's tight.

Edit:
* if I use slic3r instead of cura, there is no part that juts out a bit like you see in the images above -- that's the situation I've been getting constant y-axis wavyness in.

Edited 1 time(s). Last edit at 10/15/2014 05:17PM by wentam.

Found the issue!

For future readers:

The issue was with the force of filament pulling on the carriage -- the only reason I didn't notice early on is because when the spool is full, it doesn't take much force. However when the spool was almost empty, it was alot harder to pull the filament, slightly rotating the x-carriage. The reason that adjusting XYjerk made such a huge change is simply because you're changing how much force you're pulling all at once -- with a high XYjerk it was being offset all at once instead of slowly over several layers, causing it to "jump" to a perfectly smooth surface.

The 2 bottom bearings are 3d printed on the x-carriage -- they seem pretty sturdy, but I'll change those out to help reduce the issue -- and then probably print a different type of spool holder, or a filament guide (or both).