How to Level the Print-Bed on Your 3D Printer
The first order of business here is to make sure the hot-end nozzle on your 3D printer is a set distance away from the print surface and that your printing surface is flat and level.
This overall procedure is described in many RepRap resources, and varies from one 3D printer to the next. Usually it involves tightening up or slackening three or four specific points on your build-bed, usually one made of PCB material and either fixed or held by spring bolts that allow the user to level the bed.
Before you start to level the bed, make sure that the other major assemblies of your 3D printer, especially the moving X carriage and vertical Z movement, are also level and at equal distance on each side.
The main sensor used to position the hot-end correctly away from the build-bed is the Z-axis end-stop. This is usually a mechanical switch that can be moved up and down or a magnetic sensor that can be tuned to a set distance by turning a small rotary knob known as a potentiometer. It’s common for a small LED to light up as an indicator when the end-stop position is reached.
If your axis doesn’t stop, or if the LED doesn’t light when the axis is sent to the home position, you may have an incorrect orientation set in your firmware. In such a case, change the setting to in your file of the Marlin firmware.
If you use a heated-bed, be sure it’s powered on and at full temperature for a few minutes (to allow everything to expand to where it will be when printing) before you set the mechanical distance of the hot-end nozzle from the bed.
Check the operation of the end-stop switches by commanding each axis in turn to the home position. Then you can set the Z-axis distance so the hot-end nozzle is spaced appropriately far from the bed. The best way to do so is to move the print head to the center of the bed. On a standard RepRap, you set this space by moving X by 100mm and Y by 100mm.
The distance you need to achieve will depend somewhat on the nozzle size and on how well you’ve managed to level the build-bed surface. Partly for this reason, a sheet of glass (which tends to be reasonably flat) is a good choice for the build surface.
As a starting point, make sure you can just slide a single sheet of office paper under the nozzle when it’s at the Z home position. Check this gap for uniformity at all four corners and in the center. Use the Z-movement buttons in Pronterface to lift and lower the nozzle.
You can then move the position of your Z end-stop on the Z axis to activate at the correct distance away from the print-bed. When you home the Z axis in Pronterface by clicking the Z Home button, the nozzle should raise and then lower until the Z end-stop is triggered. If the spacing is still not correct, move the Z end-stop slightly and press the Home button again.