Leaning Zig Zag Prints

hey everyone,
I am new to this 3D printing community, i have made my first PLA 3d printer. I cant find my problem on the internet and its really weird. When i try to print a rectangle (or any shape for that matter), layers are getting shifted at periodic intervals. it's forming wavy structure when it should be straight!! I am using Repetier Host and Repetier Firmware. I directly print from the SD card on the Full graphic smart controller (reprap discount). NO sticking issues. And i dont think it can be a belt slipping problem, this is clear i guess from the pictures i have attached, the print is leaning to say left side for some layers and then leaning right for some layers, and the whole pattern is being repeated throughout the object height. All the objects have the same wavy feature. there is no such wavy feature in the stl file. I have printed a hollow calibration cube of 20mm but it has shown same wavy patterns at same height. PLEASE HELP! Thanks

It was supposed to be rectangle of 25x15x30..:

A spiro coaster i printed, since height of object is less, wavy nature is not prominent other than edges

Please don't post the same topic in multiple sections but do provide as much information as you practically can that might be relevant to your problem.

I assume from where you posted this that it's some kind of Mendel derivative. What kind? Is it from a kit? What is the primary structural material of the frame? What electronics are you using? What software are you using to slice? Have you watched the machine go to see if something is bending or getting snagged as the Z axis moves up? As bad as that is, something should be obvious.

umm ya , i didnt understand at first where my problem is, so i posted it in printing issue as well hoping for solution.
Anyways, no this is not from a kit, support structures and everything : Aluminium. Ramps 1.4 with mega, using slic3r along with repetier firmware. The z axis is free as it moves up...
What are ur thoughts? I dont think personally it can be hardware issue.. the zig zag feature is so much exactly the same, it looks like its purposely made like that.. i mean if it was hardware problem, then irregularities should follow... I dont know what to do. pls help

Please past the gcode for your cube somewhere Pastebin for eg

As you say It looks to perfect.... so first thing I would do if check the gcode, try uploading to this online viewer [gcode.ws]

Second thing is what type of machine is it? im guessing its not a Cartesian or a delta but something more weird like a polar or sacra

If it is a standard Cartesian I would think maybe your pulleys are loses on the stepper motor shafts, not enough to fully rotate right around, but so that that can turn back and forth till the grub screw hits the edge of the flat on the shaft.

Edited 1 time(s). Last edit at 07/20/2016 06:56PM by Dust.

It's a standard cartesian printer... i checked on the pulley screws on stepper motors now,(unfortunately) they were tight totally... And the problem is same, may it be a cube or a spiral structure..
the gcode for cube: 20mm_hollow_cube.gcode

Edited 2 time(s). Last edit at 07/20/2016 07:28PM by Omniaa.

pictures of your machine might also help....

uploaded Gcode looks fine.

Edited 1 time(s). Last edit at 07/20/2016 07:32PM by Dust.

So, without it being a kit we're completely in the dark. Belt-driven bed moving in Y? Nozzle on a belt-driven X carriage carried by a Z axis positioned by M5 studding?

picture of machine(home made) ... it has bed in z axis.. x and y carriages are belt driven.

Interesting bed arrangement, you 100% sure its doesn’t move around in the X and Y axis?

it does a bit, i will fix that problem.. thanks a lot

thankyou so much, i made a new printer with a better bed arrangement, which has two lead screws and 2 smooth rods... now its all working fine.. it was the bed's wobbling that was creating all the problems..