Lines in my 3d Printer! Help!

[edisonpaul4]

Hi!, I am new in this world of 3D printers but I think I have been doing well with it..

The problem started when I noticed that all my printings were almost perfect except for one thing... In the Image you will be able to see some lines every some layers! Pleas help me

What do you think is the problem?
I have a Prusa i3 from MIXSHOP.COM

[3dkarma]

Take a look at the Z-banding article in the first issue of the reprap magazine. Sources for banding include:

* A bend in the z-axis threaded rod / lead screw, where the rod / screw is constrained at both ends. Freeing one of the ends and/or replacing the rod/screw solves the problem.
* Rounding error in the number of steps per layer, causing some layers to be stretched too high while others are compressed and bulge out. Solved by making sure your layer height is set to a whole multiple of steps for your Z axis. Check the reprap calculator for the optimal layer height for your printer.
* Missed Z axis steps, causing two or more layers to be printed at the same height. Check if you have this problem by measuring the height of a completed print and comparing it against the detected height. Confirm by getting your printer to raise or lower by (for example) 30cm and listening for missed steps. Cure by increasing the vref on the stepper driver for the Z axis. Note this may also be caused by overheating of the driver. Cured by directing a fan at the driver.

There are other sources generally caused by mechanical issues, such as loose Z axis nuts. Read through the article and you'll get a good idea what might be causing the problem.