flow rate gone to the dogs...!!!

my z artifacts have gone from near perfect from the object on the left to the object on the right.. I know it is some kind of flow rate issue but cant seem to figure it out ... checked the extruder steps twice... checked the pid tuning of the hotend... but cant seem to get it ... The only thing i changed was the linear bearing on the z axis and the extruder main gear as it had snapped on the axis... the new gear is better than the old one..

any ideas???

the hot end is a j-head with a 0.4 mm nozzle and the print is done at 0.25mm layer height... the printer is a mendelmax 1.5... the z axis threaded rods are m6 rods... and the z axis is set to 1/16 microstepping...

Looks like z wooble. Changing the bearing must have increaae your z tollerance, and now it is transfering to the print.

my z axis has a z screw isolator like this one

thingiverse

so i doubt it is that .. also it is not so regular as z wobble

Have you checked the filament? Inconsistent size will cause exactly that problem

okay after lot of breaking my head did a check on the extruder motor pushing the filament.. it turns out that there is a variation in the amount of filament pushed... i ran a test to push the filament 50mm and the actual length pushed varies randomly by 5-8 mm....

any ideas whats causing it...?? the motor driver is set to 1/8 steps and it is a generation 4 electronics motor driver... also checked if the filament is slipping and it is not...

If the teeth in your gear are clogged, it can prevent good grip on the filament. Also short teeth.

If the center hole on the gear is not "centered" this will turn in an oval. Making varied extrusions.

Also, trying to push the filament too fast. If your extruder motor has high enough torque, it won't skip. Causing the gear to turn and cut a groove in the filament loosing friction. Either turn your heat up, or turn your speed down might help.
On the same note. If your motor doesn't have the torque, it may skip steps. Causing inconsistent extruded lengths.