Y slip but then again not

Hi All

I dont understand this one. My printer seems to slip in Y while printing long lengths however when I tested it with the .4 thin wall stretched by 2 in the Y it was fine. see attached

I have calibrated the XYZ axis to 0.02 in movement and as you see long thin wall worked fine

is a closer shot of what it did trying to print a spring from thingieverse

then is a calibration test, now i was expecting the Z axis to fall over at 45deg ish but NO its printed straight. I need a fan fitting to stop the twist n sagging but thats later. The calibration test is also 60mm long on each axis and thats what its printed when measured its just moved every couple of layers in the Y every now and then.

Oh and it isnt regular shift either, some layers have printed 3 layers before shift then its done up to 10 more layers before shifting again!!!!

Any ideas as its doing my head in

Mike

You need to turn up the current on your steppers a bit. The frequency response of the printer's frame sometimes creates higher loads on the steppers than the programmed acceleration limit.