Prusa i3 ruining my life (again)

The first picture is the test print after the printer had been off for half a day or more. The second picture is the same test print, printed last night after the printer had been running a long time. I dont know if those two things are related.

Problem:

Smooth y-axis shift towards the back of the printer. (not stepped)


Must Know:

Happens on all sizes and shapes of prints
Just started happening, I have been printing fine until the other day. (its not loose pulleys, keep reading)
I am working with the basic slicer wizard setup settings.
does NOT shift the same at all times. It seems to get worse the longer I keep the printer running.
After keeping the printer off for half a day the shift is almost not noticable for about 5-10 layers.

I have tried:

Reducing my acceleration to 1000m/s^2 in the EEPROM setting on Repetier
Checked for loose pulleys on the belt but they cant be! I literally epoxied the pulleys onto the motor when i built it to eliminate that problem.
Relieved tension on my filament spool during a print
Changed filaments
Checked for sliding prints but they're secured nicely with blue painters tape
Checked motor temp with hand, noticed it was hot, and added a small fan to keep it cool. It now stays cool but still shifting.
Printing with slower settings (didnt like this sollution because i was printing on normal settings fine before)
Tried varios sizes and shapes of prints
Testing my belt tension, but it seems ok. Its not so tight as to add friction, but I have to try to squeeze it together with my fingers.

ty everyone

Edited 5 time(s). Last edit at 12/07/2015 07:13PM by davidbananas999.

Have you tried reducing xyjerk?

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fixerT
Have you tried reducing xyjerk?

no i havent. What does it do?

If it is the y-axis of a Prusa it can be binding linear bearings. Do they rattle while you move the bed by hand?
Move slowly or unplug the stepper without power ON, fast manual moves can destroy the y-driver !
-Olaf

I will remove my heatbed when i get home from work to check the bearings. I believe the bearings they included with my kit were the same ones that have good reviews on amazon. I have not compared model numbers, but they look the exact same. I do believe my problem is mechanical. Are there any tricks to tighten the bearings to my plate without twisting them as the screws tighten? Im sure it has to be damn near exact. Thanks

Quote
davidbananas999

Quote
fixerT
Have you tried reducing xyjerk?

no i havent. What does it do?

Sorry I read your message more carefully: I thought you had sporadic shifts in the y-axis, but I now understand you have a consistent smooth shift... So xyjerk won't likely fix this.
Have you checked that the y-driver doesn't get too hot? Is the current too high on the y-driver? Do you have heatsinks on the drivers and an electronics fan?

High current/temp on the y-driver is consistent to what you are saying. First layers would print well and soon the driver would heat up and would start missing steps. That would also explain the heating of your y-motor.

Ok so i removed my bed and plate and checked the bearings, and the movement was pretty rough. I wiped down the guide rods with silicone spray lube and sprayed some inside each bearing. It felt smooth when i manually moved the heat bed etc but i guess it wasnt what it could be. I will put everything back together after dinner to see if I changed anything. So maybe the friction on the y was causing things to work hard and overheat? I would appreciate a link to some 8mm linear bearings that someone knows works well from experience, just in case the bearings I have are bad. Mine are square with 4 mounting holes.

thanks

I just put everything back together and the heat bed is moving much smoother! It glides nicely. I just started a test print so fingers crossed!

It looks like a problem I was having with layers stepping in the y direction. I adjusted my X, Y and Z pots from .5 to .7 volts and that cured the problem. The higher setting gives the motors a better clamping force.