False "print exceeds bed size" warnings on Prusa i3 mk3


Hello everyone, I'm back in OctoPrint after purchasing, building, and calibrating a Prusa i3 MK3. Gotta say - this is one hell of a great printer. Compared with my old FlashForge Creator Pro, the MK3 has been much more reliable and has produced prints with much better quality (and I haven't even tried the high-detail setting yet).

I've also completed a transition to OctoPrint, and it's working great - with one small issue: the bed size warning is occurring with nearly every print. This is odd because I'm using the PrusaPrint image, which of course is preloaded with MK3-specific settings; I'm slicing and G-Coding with the version of Slic3r right from Prusa; and I'm printing small, typical things that take up the middle 1/9th of the bed and aren't more than 10cm tall.

I see that the "bed size warning" feature is listed as beta. I'm interested in helping to debug by providing diagnostic info, but I'm not sure how to access any diagnostic info for this particular feature. If someone can point me in the right direction, I'll provide some data after the next warning.


A lot of the time it's because the printer moves to a negative value to wipe or purge the nozzle. I'm pretty sure prusa's move to like -something and do a purge line, that puts the "model" size at larger than the bed, octoprint doesn't know the difference between a purge and a printed wall. So while the build volume might be say 200x200 (yes I know they're bigger than 200x200, just go with it), that negative space it uses is reserved in the firmware so your actual build volume is more like 220x200.


Hello @sfsdfd,

note that the size detection is still BETA status. It can result in errors with some models. You can switch it off:

And here are the settings of my MK2.5:


Looks like it was also asked on 3d.stackexchange and an answer was accepted: