Print 'drifting' on X axis towards the back of the bed

I'm having a slightly strange problem.

Last weekend I fixed the heat bed on my I3 (i'd originally got the heat bed element upside down). I then levelled the bed, and printed a few small parts fine.

However when I printed something larger i've noticed something very odd - towards the back of the bed as it moves up (z) in layers, the print drifts to the left, however at the front of the bed the print stays aligned.

All I can think of is that the cable routing to the heat bed has changed, and is causing the problem, but I would have expected the drift to have been less even, overall it appears as if there is a twist in the print.

I would appreciate any suggestions to try ?

Peter

Your bed has such lousy bearings, that the cable tension has an influence?
Does the table run free from front to back? Maybe one smooth rod is a bit tight at the back and forces the table to twist.
-Olaf

If the effect is a function of the z axis, check if the z smooth rods are perfectly parallel, and square to the print bed. Also check if they run smooth without binding. Is the cube square at the bottom and sheared at the top? probably both z and y smooth rod are non parallel and/or non square to the other axes.

I've sorted the problem - when I flipped the heated bed, one of the cable ties holding the rear most bearing for the bed had come lose.

That was causing 'slop' when the bed was towards the rear - replaced the cable tie and tightened up and all is well.

Thanks for the suggestions, most helpful

Peter