Heatbed leveling

Bed levelling is very important. It's a part of succssful printing. When bed isn't leveled right, your prints are not sticking or layers may be too thin. When your printer is running smoothly, filament is being extruded at an even rate because of pressure from the filament behind pushing it forward. The resistance to this plastic being pushed is referred to as “back pressure”. When the space between the nozzle and print bed vary from different places, the space the filament has to flow into changes which varies the resistance of filament flow. This variance in pressure can cause extruder jams, inconsistent extrusion, and gaps in your layers.

The process of levelling is mostly same for 3D printers. I will discribe Anet A8 bed levelling. You will need one A4 paper sheet and screwdriver. If you use painters tape or other heatbed covers, you need install them first. I use painters tape, but I have thought replacing it with glass plate. You need to heat up your heatbed to printing temperature, because aluminum plate will expand and contract when they are heated and cooled so if you want your bed to be accurately level, it’s best practice to do it when the bed is in the same state that it will be when you print. 

Then you have to loosen four butterfly nuts in every corner. Move your print head to the centre of the plate and place the paper sheet under the nozzel. Loosen Z-axis endstop screws. The endstop switch keeps the nozzel touching the hotbed. Lower the print head by turning both couplers at the same time. Adjust the end stop of the Z-axis until you feel a slight resistance when you try to move the paper sheet underneath the nozzle. This means you can still move the paper front and back, but the nozzle is causing some resistance. If you can move the paper too easily and there isn’t any resistance then the nozzle is too far away from the build plate. If the paper isn’t moving at all, then the nozzle is too close and you should adjust the build plate slightly lower.  

Move your paper and nozzle head to all corners of your printer and make sure that there is no resistance underneath. Adjust the bed height with the screws on the corners of the bed.  Start in one corner and get your print head as close as possible to the bolt and put the paper underneath the nozzle. Use screwdriver to adjust the bed until there is slight resistance on the paper from the nozzle. Repeat this step in all the corners of your bed. You don't need screwdriver when you drill through the heatbed holes. Then you adjust height by turning butterfly nuts. 
  
Once you’ve levelled all the corners, repeat this process again. When you make the adjustments in the corners, it also affects the other corners so it may take a few times to get it just right. 




The levelling takes time and you should do it often. If you are tired of it and are willing to spend some money, you can buy auto levelling sensor. There are many different type of sensors. Some of them are optical and others are touch sensor. Auto levelling makes it easier. I bought sn04-N sensor. I installed it with Skynet firmware. It works great, but I had some problems too. You can get it at these sites: Site1 and Site2