Print moves mid print when printing large objects

When I print small objects it prints great, with larger objects the first few layers print find then the print moves, at first it kept moving backwards, I adjusted the stepper pot and didn't make a difference, then I tighten the y belt and now it's moving the opposite direction, any ideas why and how I can fix it I'm using cura to slice, and thank you in advance

There are many reasons for "skipped steps" which is the term you should start searching with.
Two reasons, which are the most popular:
Stepper current to low => adjust Vref
Over-Extrusion causes the nozzle to bump into the print => calibrate e-steps

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o_lampe
There are many reasons for "skipped steps" which is the term you should start searching with.
Two reasons, which are the most popular:
Stepper current to low => adjust Vref
Over-Extrusion causes the nozzle to bump into the print => calibrate e-steps

Correct, and one more reason that frequently occurs. Printing vertical holes. When the printer is busy printing the uppermost part of a vertical hole the two 'points' of that hole will curl upwards and nozzle will bump into it. In combination with a bit overextrusion. Same with outward sloped perimeters. Especially at the corners that part will curl upward, again resulting in bumping the nozzle in these high parts, skipping steps.

Ok I adjusted the stepper controller and it's working fine except the prints are splitting in the middle, I raised the temp on the extruder and the bed, but it still splits around the same area-ish but prints pls fine, also printed abs with can off

Whats your layer height? Rule of thumb is to not set it greater than 80% of nozle diameter. So for a 0.4 nozle don't use layers greater than 0.32.

It is a 0.4 nozzle and later height is set to .3 on slicer

My printer is a i3 style and not in an enclosure could that be the problem it prints pla fine

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nukes88
My printer is a i3 style and not in an enclosure could that be the problem it prints pla fine

ABS shrinks alot, to control this there are several rules.
First rule, NO FAN there are times when you can use your print fan but its really just when bridging.
Second rule, enclosure!!! Heated is better... you should have your ambient air temp around your print around 60c

your pic shows me your fan was causing the layers to shrink and pull away from lower layers.
Turn off your print fan and it will do better, but without an enclosure to keep the temp up at least 40c you will just not get very good prints.
If your not willing to make an enclosure I suggest you give up on ABS and try PETG....

Edited 1 time(s). Last edit at 02/23/2018 07:08PM by JustSumGuy.

I made my own liitle enclosure by printing a 2 perimeters thick skirt around the part. The skirt requires a very good print surface, like the ( fake? ) PEI sheet I tested. I can't guarantee, bigger ABS parts won't crack, but the temp inside the skirt was high enough; I had to use 30% part-cooling to keep the part from softening.

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o_lampe
I made my own liitle enclosure by printing a 2 perimeters thick skirt around the part. The skirt requires a very good print surface, like the ( fake? ) PEI sheet I tested. I can't guarantee, bigger ABS parts won't crack, but the temp inside the skirt was high enough; I had to use 30% part-cooling to keep the part from softening.

[attachment 102873 2018-02-1710.27.36.jpg][attachment 102874 2018-02-1710.27.51.jpg]

Neat idea! There is one I intend to give a try!