Hi guys, been playing around with my Prusa i3 to get it right.

Problem I've now is that after leveling all the 4 corners the bed is closer (0.3 mm) to the nozzle in the middle of 2 corners.
I am using a MK3 heat bed with on top of that a 200x200mm plate of glass. I reckon it has something to do with the X-axis because the glass plate is pretty straight

Any help is much appreciated.

Edited 1 time(s). Last edit at 03/13/2016 11:45AM by permans.

a lot of us are working on that what I find happening is the plate attached to the y axis rods with bearings and belt clips that your bed sits on is bending when you tighten/adjust the four corners especially on the diagonals from each other the front left becomes too close and as you tighten to increase bed gap it causes the back left to go farther away from the bed .If you undo the leveling screws and remove the heat bed and press on the four corners you can see how it bends. I am currently working on a solution with either a steel or aluminum replacement for the bending part or adding an additional bearing to the plate. Also make sure both ends of x carriage is the same height from the base of z steppers adjust the one opposite to x stepper by turning that Z stepper up or down to. For now I forget about back left and get other 3 close ok for small parts when I solve I will post findings

---

rwt

You have not stated the exact model so I have to assume some things.

Make sure your printer base is absolutely SQUARE. To do this place it on a level, hard surface, loosen all the base screws, press the printer base down and re tighten all the screws.

If you think it could be the X axis then try this.

Screw down your bed leveling screws in all 4 corners down to the exact same height. To assist this, use a small piece of wood that is about 10 mm height or so. Put it between the heated bed and the plate and screw down the bed leveling screws. This is not very accurate so be aware of that.
Now all 4 corners of your bed "should" be at the same level.

Move the Nozzle to the FRONT LEFT corner (about 10,10) and HOME the Z axis. Adjust the height to the bed by adjusting the SCREW for the Z axis stop switch, NOT the bed screw. Once you get the proper height, back it off a bit as this will change when other corners are adjusted.

Switch off the motors/printer and move the head to the FRONT RIGHT corner. Given that the two front corners are at the same height, the same because you adjusted them with the wood piece, now with the printer still off, twist the Z axis ROD BY HAND up or down till you get the proper height between your nozzle and the bed. Do not adjust with the bed screws, but just by turning the Z axis rod.

Now the front 2 corners are adjusted - meaning your front 2 corners are parallel to the X axis.

Continue with the other 2 corners but use the BED leveling screws again to level.

Once you are happy, then switch on the printer, Home the X and Y and then HOME Z in the very middle of your print bed. Adjust using the Z endstop adjustment screw.
Now move the head to the Front Left, Back Right, Back Left and Front Right and adjust using the BED leveling screws. Do this 2 or 3 times and your bed should be level.

HTH