A good first layer is the foundation for any successful 3D printed part – unfortunately getting the perfect first layer gets more difficult as your build volume gets bigger and bigger.

Additionally there are numerous factors surrounding what can influence how well your first layer will be laid.

These factors include, but are not limited to:

• flatness of your build plate, including the magnet and print surface.
• extrusion profiles that make up the X and Y axis
• accuracy and consistency of the probe used to level and mesh the bed (this applies to both inductive and microswitch style probes)
• alignment and general assembly of the printer as a whole

These were thought to be the main factors influencing  first layer accuracy and consistency across the build surface until Voron community member whoppingpochard#2514 considered frame expansion as a result of heat as a possible factor aswell.

What followed was the following deep dive and investigation which can be found in detail on his github here:

https://github.com/tanaes/whopping_Voron_mods/tree/main/extrusion_backers

The resulting findings showed that the heat generated in the chamber was significantly affecting first layer consistency due to frame expansion and bowing.

Gantry backers proved very effective in combating the various levels of expansion that would occur during varying ambient chamber temperatures.