The smooth rods on the Wanhao Duplicator i3, being made of a less than highest quality material, can develop a bow or bend.  This can result in difficulty leveling the bed.

Bent X-Axis Rods

Bent X axis rods typically cause leveling problems in the center of the bed.  If you can get consistent leveling on the left and right sides of the bed, but the center is either too close or too far away, AND you’ve ruled out the bed itself as being the problem, it’s very likely the X axis rods are bent.  If the nozzle is further away from the bed in the middle than it is on the sides, the rods are bent up.  If the nozzle is closer to the bed in the middle than it is on the sides, the rods are bent downward.

To resolve the problem, you can replace the rods, or try to adjust the rods to compensate for the bend.

  1. Make a small mark on the lower rod with a Sharpie.
  2. Loosen the set screws at each end of the rod.
  3. Rotate the rod 180 degrees using the mark as a reference.  This is easiest if you make the mark on the front side and rotate the rod so the mark is on the back side.
  4. Tighten the set screws to lock the rod in place.
  5. Relevel the bed.

Now, one rod will be bowed up and one rod will be bowed down.  The rods will now be pulled together or pushed apart by the bearings, the bow of each rod cancelling out the bow of the other rod keeping the extruder centered between them.

If this does not resolve the problem, further disassembly and investigation may be necessary.

  1. Remove both X axis rods.
  2. Roll each of them on a known flat surface to help identify the severity of the bend.  If only one rod is bent, it will need to be replaced.  Or you can attempt to bend it back straight.
  3. If both rods are bent equally, use a Sharpie to mark both of them on the low OR high side.
  4. Re-install the rods using the marks to orient the bows in opposite directions (one rod bowed up, one rod bowed down).
  5. Relevel the bed.

To prevent the problem from recurring, only replace filament with the extruder at the far left or far right of the X axis where the bars are well supported.