Stripes on Z axis

I was trying to print mendel max1.5 parts and i started with easy ones but i have come acros a problem. All those prints have stripes on them. Ones are bigger other are smaller and every stripe is in the different place on different part. I'm not sure what causes that but i would like to fix it somehow. I'm using slic3r. Printing in PLA 1.75. And i'm printing on my own project of delta printer. Those parts were printed at 0.2 resolution. Can someone help me somehow? [imgur.com] [imgur.com] [imgur.com]
Could this be possible of bad quality filament or is it something different?

Edited 1 time(s). Last edit at 07/28/2015 02:04PM by AFK-er.

Looks like under extrusion to me.
You should inspect your filament diameter along the hole spool ( wind it on a temporary spool )
Thinner portions will have a double effect on the printed part: The extruder slips easier and the part gets less material.

Another cause could be a dropping hotend temperature for some reason. But I can´t make up any scenery where this would happen and cure itself.

-Olaf

I have inspected the filament diameter and i found that it jumps from 1.70 to 1.76 so i bet this is it. Will have to buy different one next time.
Could this be problem of some sort of looseness? I'm kinda curious about it but i'm not able to try different filament to test it on... at least in this week.

Edited 2 time(s). Last edit at 07/29/2015 11:34AM by AFK-er.