One of the critical parts in a FFF 3D printer is the extrusion nozzle. It's that part that lays the rubber on the road. The exact flow of plastic is determined by temperature which affects viscosity, filament feed rate which is pressure, filament size which is volume. Put those factors through an orifice of a specific size (which then is a metering device), the exact flow can be calculated. The nozzle is the orifice but it also determines the initial diameter of the extruded plastic.
Just after leaving the nozzle there are a few more additional variables which are separation distance of the end of the nozzle above the deck or previous layer and the rate of travel of the nozzle following the commands from the computer code. There is also a cooling factor along with departure temperature that that determines how much the plastic will flow or be compressed. Then throw in shrinkage (warping) to keep it interesting.
No, I don't have all the magic setting numbers. The operator (print master) has to understand all these flow variables.
The design of the nozzle is fixed, although it is certainly permissible to experiment with designs and hole sizes. A few more variables to add to the mix.
Here I have taken a closer look at the standard 0.40mm print nozzle under the microscope. The hole is far too small for these 70 year old eyes to see anything unassisted. The hole is just as critical as any of the other factors in the printing formula. It needs to be understood as much as the numbers plugged into the setup.
Sometimes I suspect a partially plugged or damaged nozzle hole to be the answer to of a lot of my "what changed now?" troubleshooting investigations. When all else fails, change the nozzle.
You can see in the pictures I have purchased a package of those 0.40mm "nozzle cleaning" drill bits. Let me be clear on this:
I do not believe in cleaning an old plugged or mal-functioning nozzle. Throw the bad one away and install a new clean nozzle. It's cheap.
I bought the micro bits for gauging the hole size in new nozzles and making sure they are perfectly clear, no burrs. Not for cleaning used nozzles. Also for making these pictures of the process. Spare nozzles should be stored carefully in a very clean place.
The short video shows me prodding the bit through the nozzle hole checking size and clear passage. The video and pictures were made through the USB electronic microscope seen in the pictures.