# How bed leveling is achieved without table screws?

I have seen printers with table screws and bed leveling sensor and printers that have only bed leveling sensor (such as Prusa).

So my question is how does the bed levelling work when there is only a sensor, and no adjustment screws? What will happen if I totally remove the table from the printer and then re-assemble it? Will the print fail or what?

• Are you asking 'will the calibration persist through dissassembly/reassembly' or something else? Your question is a bit confusing, Jul 11, 2018 at 10:30
• RealMen(TM) always level manually like the universe intended. (Shamelessly stolen from some stick-shift enthusiast) Jul 11, 2018 at 12:29
• @SeanHoulihane Yes, exactly that. Jul 11, 2018 at 19:17
– 0scar
Sep 9, 2018 at 22:45

Prusa uses 9 marker points in the bed that are sensed with an induction sensor to determine the X, Y and Z position. Any deviation for skewness or bed level is compensated through the software. Please do note that the bed is pretty level to begin with (by design).

This is precisely described here, please check the video.

Note that Marlin Firmware (which is basically what drives the Prusa printers) has skewness compensation implemented. This is implemented in the configuration file, and found under header Bed Skew Compensation. You basically print a square and measure the diagonals and insert these measurements into the configuration file. Prusa printers do this automatically by using the measurements of the marker points.

• One question to the auto leveling: If the bed is tilted and the autoleveling measured this and then the printer adjust the z axis over the position on the bed, will a x-y-point on the first layer be located exactly under the (in model) same x-y-point in a higher layer, or will it be shifted to? I mean, if the bed is 1 mm lower on one side over 10 cm then a top corner of a 10-cm-cube should be also 1 mm shifted, so that the cube sill is real cubic and not sheared. Jul 11, 2018 at 6:06
• @Horitsu The bed level is usually fading out over a predefined distance, in e.g. Marlin #define ENABLE_LEVELING_FADE_HEIGHT determines that, and the height can be set with M420 Z<height>. Yes, a cube will not be perfectly cubic, that is why even with auto bed leveling you need to provide a bed as level as possible, it only should correct for very small deviations.
– 0scar
Jul 11, 2018 at 6:18
• @Horitsu Your comment contains a valid question that contains information to ask here on SE.3DPrinting. I'll be happy to answer it again in more detail.
– 0scar
Sep 9, 2018 at 22:52
• @0scar It is a bit hard t tell from the original question, but I think you can reasonably include this extra detail in this answer. 'How does bed-leveling function' includes the aspect in the comment, and a good answer would make this a good 'duplicate target'. Sep 10, 2018 at 6:17
• @0scar i posted it as own question, I'm exited for the answer Sep 13, 2018 at 5:58