It´s imperative that you always monitor the printer during the initial parts of the print, making sure everything is going well & checking for possible issues that may occur allowing you to stop the print if things go wrong. It´s not recommended to use the 3D printer unmonitored.
You may encounter several issues in the world of 3D printing that is related to the very first layer of the print. The following are typical symptoms of a faulty first layer.
- Parts lifting (warping)
- Parts coming off the build plate
- Layer shifting
- Parts too difficult to detach from the build plate without damaging the plate's surface or model
- Blobs and print irregularities
- No extrusion at all
Majority of the issues above would be caused by a combination of poor adhesion to the build plate and the first layer not being set correctly. As the part would lift (warp) it could obstruct the correct amount of plastic from being extruded (under-extrusion) or the plastic being forced to go over the sides causing blobs. If this would continue throughout the print, it can also cause a complete disruption of extrusion. A lift like that can also cause the printhead to collide with and catch the model while moving, getting stuck and the motor will skip steps and then cause layer shifting.
Even when having a printer with automated or semi automatic calibration of the bed and extruder, it is a good practice to know how to identify a good first layer and if needed make the proper adjustments to get one.
Think of the extruded line of plastic like a garden hose. If you just lay it on the ground, it remains round, and there is very little circumference surface touching the ground. 3D printing in this manner means that an insufficient amount of plastic adheres to the platform, possibly causing insufficient adhesion. If you are not monitoring the initial part of the first printed layer, you may end up with a big blob of plastic surrounding the print head.
On the other hand, if you step on the hose forcing it towards the ground, it will be almost flat. In 3D printing terms, this is not good either as the plastic may stick too well to the platform and probably causing damage to the build platform by scratching the nozzle onto the surface. When suffering from insufficient layer adhesion, it can sometimes be tempting to intentionally adjust the platform closer to the nozzle forcing the plastic onto the surface. While this can be done in some cases depending on the plastic and surrounding circumstances, it needs to be done with care and not too much. Knowing where the limit is can be a powerful resource.
Referring to the garden hose analogy, a perfect scenario would be to apply enough force to the hose and just squeeze it enough to shape it like an oblong. That will yield the best result and platform-adhesion for the first 3D-printed layer. It also means that enough plastic will touch the buildplate and the outside of the extruded line will connect evenly to the adjacent line of plastic. As mentioned earlier, depending on kind of plastic and other surrounding circumstances, a varying amount of pressure can be applied to get the optimal distance/layer adhesion.
Of course the above is also very dependent on a clean and properly maintained build surface as well as a correctly leveled build plate.