Protractor for MK3S bed levelling

If you have modded your MK3S print bed so that you can level it by adjusting the screws you might use the “Prusa Levelling Guide” plugin in Octoprint to get information about how your bed needs to be adjusted. I find the most convenient output to be in decimal turns. That means if the bed is the height of one turn too high at a particular point, the software will tell me to turn the screw “+1”, or one turn clockwise. As the height becomes more and more correct it gets down to fractions such as .5, .1 etc. When the entire bed is close enough you are perfectly level and it's time to print one of those perfect first layer test prints.

(Mine uses one of the original standoffs + one M3 washer in the center position. The remaining 8 screws have a nylon washer against the bed with some dielectric grease to help it turn freely and then two M3 nuts locked tight against one another with a little thread lock. Don't get the grease and threadlock mingled or you may as well take them off, clean everything and start again. When the eight peripheral screws are tightened down and then backed off one full turn this makes the eight screws within one turn of level with respect to the central screw, tightened snugly.)

If you are guessing at how much to move the hex key for a specified turn it always takes longer. This protractor is designed to slide along the shaft of the hex key so that the key will describe an angle on its face when it is moved. Each circle in the protractor represents .1 of a turn. If you start the slot at the same orientation as the key then you have one circle at every increment of .1 turns and you can more quickly approach the perfect bed level.

Just about any print method will do for this item, I used PETG. I tried with “.1”, “.2” printed on the top of the unit but even with the finest nozzle it is just too small, far easier to count the dots.