I know some of you here have built your printers from scratch so im hoping one of you will be able to shed some light on my current issue. I have some Z banding on my printer i cannot seem to figure out. It was originally an Prusa i3 MK2S but i changed it over to a 3030 aluminum extrusion frame. Everything ran fine for a few weeks but now everything i print looks like crap.
Check for something loose…
Nothing loose 
I have replaced just about everything except the motors with no progress
Increase temperature and reduce speed slightly .
clean x/y belts and Pulley - maybe some dust lead to irregularities.
bvuogh
@Ulrich_Baer already replaced both belts and pulleys
I’ve had such a problem, uneven extrusion!
Somewhat friction and dispersion is unevenly distributed. Watch how thread is threaded when you’re on the move, you can not get it somewhere. The spring force should be appropriate to the extruder.
Have you got couplings on the z motors? Could be that their slightly misaligned??
Can you post a pic of your z axis?
Only one i have with me. I dont have couplings i use lead screwsmissing/deleted image from Google+
This is what i meant. It negates any slight differences in the threaded rod. Are your z screws directly attached to the steppers?
have you checked the filament or does this happen with different filaments?
Try printing a calibration cube. Then you will be able to see if the banding happens on all axis or just z.
Maybe try changing your flow rate in your slicing software. It kinda looks like it’s under extruding. Have you tried a different nozzel or filament? Are you sure that your temps are accurate? Maybe your thermistor is reporting an incorrect temp and you’re running too cold.
@Jonathon_Thrumble the screws are built into the steppers yes
@Kevin_Danger_Powers gonna replace the hotend assembly today i have a brand new one
I have struggled with this from time to time myself and found several things can cause it. I would start with the previous suggestion of printing a calibration cube. It will allow you to see if it’s shifting in one specific axis.
One printer I struggled with this on was actually an issue with the Y axis not moving smoothly. I can’t tell from the picture whether your y axis is on rods, wheels or a slide. Check wheels for wear, good contact with the extrusion, and smooth rotation. If your using rods check that your bushings move freely, and that your rods are completely parallel. Look for any bolts hanging down that might rub or catch on something.
Another machine had it from the x axis being off level from side to side.
Check the vertical alignment on your lead screws. Are they the same distance from the frame on the top and bottom, or do they lean from left to right? Bent lead screws can also be a culprit. In your case that would involve replacement of the stepper motors as well.
Check to see if your stepper motors are overheating. This can cause random missed steps by itself. If they are getting hot check your vref voltage first. If that is good (I set mine around .8 volts) then start looking again for mechanical issues. Overly tight belts and axis out of square can be the culprit.
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Over-extrusion will cause surface finish like this… try cutting your extrusion multiplier to ~80% of whatever it is now, just as a quick test to see if the appearance changes.
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White filament often has performance issues due to extremely high pigment load, and it shows flaws better than other colors too… try a different color (not black) to see if it looks any better.