Thanks for your suggestions. I did wonder about skipping steps. What puzzles me most is that the error is so consistent. I would have expected skipping steps to be a bit more random. When the problem manifests, each layer seems to be offset by the same amount. I have indeed checked the leveling. I've checked the tension to ensure there is no slippage twixt pulley and fishing line, though I had not considered it might be too high. The carriages move very freely (everything uses ball bearings), so I don't think that the the torque required is high enough to cause the steppers to missing steps. The motors don't even get hot, which implies to me that the torque is not excessive (the extruder drive does, because that's working hard). The hotend temperature is between 210 and 220C. I'm printing PLA. If it were dragging or catching, I'd expect the same effect on an "identical, but slightly smaller in the x direction" model. In fact, the issue goes away completely if I reduce the x size from 200 to 175mm.
Speed and layer height seem to have no effect on the slant. I have not tried printing with a raft - what is your line of thought there?
Speed and layer height seem to have no effect on the slant. I have not tried printing with a raft - what is your line of thought there?