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Pattern seen on sides of cylinder

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I am a beginner, having great success with the Ultimaker 2 but need help understanding something. There is a pattern showing up on my models. I am printing a model 1.2” D with offset hole inside 0.75” D, 0.53” tall and hole on side. Best appearance is obtained at defaults. All models regardless of location printed on base plate and rotation of the model have an offset pattern half way up. Pattern is evident on opposite sides (inset on one-outset on the other) and happens at the same physical location for the printer even when the model is rotated 90 degrees . I changed temp and speed which degraded the print but did not change the pattern. What is happening and is there anything I can do to obtain smooth sides on the cylinder? I have pictures but can't figure out how to attach them.

Thanks in advance for any help.

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To upload a picture you click on the second icon from the right above the area you're typing your text in. Switch tabs to "Upload image" and the rest should be fairly straight forward.

I think a picture is needed before making any real suggestions.

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Could be a few things but I'm going to start with backlash and check some things.

Does the pattern:

1) Stick out on the far side also?

2) or is the whole part shifted in one direction (left and towards camera) such the far side center band move *inwards* towards the center of the part?

If #2 then it's backlash - something is loose or too tight. I'll tell you more after I hear your answer. If it's #1 it's probably over or underextrusion caused by speed changes at the hole - to verify slow it way the hell down - try 25mm/sec. Report back.

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Thank you, I am running a different print at the moment so it will be a while before I can try your suggestion. I did rotate my model 180 degrees on the build plate and the pattern stayed at the same physical location of the build plate even though the side hole location had changed. It is similar to a shallow V laying on its side. It appears the entire layer is offset. the pattern extrudes on the side, then indents at the first edge of the inside hole, extrudes at the far side of the inside hole and indents on the opposite side of the part. I also printed at a different location on the build plate and the pattern appeared similar. Most everything else I have printed so far is only 1/4 inch high so I don't know if this happens on different models.

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Okay so this sounds like backlash (aka play). Backlash is usually something loose. Backlash is when you move X axis to the right to say position 100, it only reaches say 99. Then when you move it to the left back to 0 it only reaches say 1 (that would be 2mm of backlash or play). This is usually caused by loose belts or crazy enough, belts too tight causing very high friction.

The reason it's different on the layers with the hole is that on some layes the head is moving clockwise and on the layers with the hole it's moving counter clockwise (or maybe the other way around) due to the hole making the slicing different. Coming at the layer from another direction makes the backlash more visible.

To fix, with no power to XY steppers push the head around gently. Feel for something loose. Alternatively feel the friction and see if one axis is much higher than the other. Consider oiling only the 4 rods in the upper corners, but not the 2 that go through the head. Check the belt tensions - the UM2 rarely has loose belts because each of the 4 blocks has a belt tensioner inside but maybe one is broken. More likely your entire head is loose and the nozzle flops around a bit. Or maybe your friction is incredibly high on one axis.

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