Bed levelling or in true terms bed traming is adjustment to how parallel the hot end nozzle travels across the surface of the print bed.

With frustration and perceverence, I was able to achieve perfect first layer adhesion, reduced z-wobble and good prints.

I would like to share a simple concept and process on how I achieved true traming without continuous adjustments and I only redo this process only if something major disturbs the printer and bed.

I am not an expert, but only sharing my observation and results from learning from my mistakes.

The picture above represents a cross-section of the nozzle and print bed assembly with a blue line representing true levelling (traming).

The print bed is made of an alluminum plate. Due to thermal expansion and contraction, metal will become distorted in it’s natural state if without reinforcement. The first picture shows, the bed is bowed downwards, and all the adjustment screws is all the way down.

All of my 3D printers as they come out of the box, the bed has a downward bow. You can measure this from the middle of your X-axis gangtree if its square down to the bed and repeat from the X-axis gangree to the edge of the bed. The second picture show, as you wind all the adjustment screws all the way up, force is applied to the edges of the print bed making the bed bow upwards. You can verify this by measuring from the X-axis gangtree as described previously.

*** Take note, the first two pictures is the bed ‘Unheated’.

When I’m traming, I do the usual paper (feeler gauge) technique to get my Z-offset and adjusting the adjustment screws to the nozzle ‘unheated’ to tram the print bed before auto-levelling.

From the third picture, the yellow line represents my perceived traming - levelling (traming) the print bed in relation to true level.

Once I auto-level and the bed heats up, due to thermal expansion, the bed bows upwards. The problem here, is that the Z-offset will compensate for any distortion of the bed, but when the nozzle prints either side of the bow, you may think your layer is level, in fact the first layer is barely adhering, due to the Z-offet has it’s it’s level computed from the bow when auto-leveling.

*** From my experience, this is why I get problems with layer adhesion.

The fourth picture, I adjust my adjustment screws, so my print bed is just a tad below actual level. As you can see the yellow line has a downwards bow. The reason for this, is to compensate for the bed bowing up to achieve true level when the bed becomes ‘heated’ during auto-level.

*** I have reduced Z-wobble. due to the fact, I have damped or reduced the Z-axis compensation andj have better first layer adhesion.

You can make refinements to the actual bed before auto-leveling by adding alluminum tape to act as spacers if your bed is badly distorted.

To fine tune after auto-leveling you can use bed meshing software like klipper.